Hurricanes and Global Warming – Is There a Connection?

Finally, then, we come back to Katrina. This storm was a weak (category 1) hurricane when crossing Florida, and only gained force later over the warm waters of the Gulf of Mexico. So the question to ask here is: why is the Gulf of Mexico so hot at present – how much of this could be attributed to global warming, and how much to natural variability? More detailed analysis of the SST changes in the relevant regions, and comparisons with model predictions, will probably shed more light on this question in the future. At present, however, the available scientific evidence suggests that it would be premature to assert that the recent anomalous behavior can be attributed entirely to a natural cycle.

But ultimately the answer to what caused Katrina is of little practical value. Katrina is in the past. Far more important is learning something for the future, as this could help reduce the risk of further tragedies. Better protection against hurricanes will be an obvious discussion point over the coming months, to which as climatologists we are not particularly qualified to contribute. But climate science can help us understand how human actions influence climate. The current evidence strongly suggests that:

(a) hurricanes tend to become more destructive as ocean temperatures rise, and

(b) an unchecked rise in greenhouse gas concentrations will very likely increase ocean temperatures further, ultimately overwhelming any natural oscillations.

Scenarios for future global warming show tropical SST rising by a few degrees, not just tenths of a degree (see e.g. results from the Hadley Centre model and the implications for hurricanes shown in Fig. 1 above). That is the important message from science. What we need to discuss is not what caused Katrina, but the likelyhood that global warming will make hurricanes even worse in future.


1. By ‘destructive’ we refer only to the intrinsic ability of the storm to do damage to its environment due to its strength. The potential increases that we discuss apply only to this intrinsic meteorological measure. We are not taking into account the potential for increased destruction (and cost) due to increasing population or human infrastructure.


Delworth, T.L., Mann, M.E., Observed and Simulated Multidecadal Variability in the Northern Hemisphere, Climate Dynamics, 16, 661-676, 2000.

Emanuel, K. (2005), Increasing destructiveness of tropical cyclones over the past 30 years, Nature, online publication; published online 31 July 2005 | doi: 10.1038/nature03906

Goldenberg, S.B., C.W. Landsea, A.M. Mestas-Nuñez, and W.M. Gray. The recent increase in Atlantic hurricane activity. Causes and implications. Science, 293:474-479 (2001).

Kerr, R.A., 2000, A North Atlantic climate pacemaker for the centuries: Science, v. 288, p. 1984-1986.

Knutson, T. K., and R. E. Tuleya, 2004: Impact of CO2-induced warming on simulated hurricane intensity and precipitation: Sensitivity to the choice of climate model and convective parameterization. Journal of Climate, 17(18), 3477-3495.

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317 comments on this post.
  1. Pat Neuman:

    The authors of this article discuss frequency and intensity of hurricanes. Another important element is the size. It was reported that Katrina was highly unusal for a combination of high intensity and large size. The slow movement inland added to the forces which breached the levees and flooded New Orleans.

  2. Jack:

    A fine article.

    Sheer — very nice in lingerie.

    Shear — not conducive to hurricanes.

    [Response: Thanx, fixed. – stefan]

  3. Magnus:

    very interesting, glad you keep this blog going!

  4. Ana Unruh Cohen:

    Excellent work again! Thank you for writing this. It is very helpful, especially the analogy of loading the dice. Ana

  5. Lynn Vincentnathan:

    Of course, statistics wouldn’t work with just one statistic. Scientists look “forward” at how various forcings are likely impact the climate in various ways, but would it be possible to work “backwards” like forensic scientists and “deconstruct” one particular climate event, such as Katrina, with whatever we do know–sort of “peel away” the most likely various factors that created Katrina. I think they did that with the 2003 heatwave in Europe, and figured about half of the deaths could likely be attributed to GW.

    We know there has been some natural SST warming and we know there has been GW contributing to SST warming. Could we “peel away” the most likely portion of that overall warming caused by GW, then figure how destructive Katrina would have been, and subtract that from how destructive Katrina actually was to figure the likely (above 50%, or even 20% certainty) contribution of AGW to Katrina’s destructiveness? Or at least come up with some high-end/low-end range? Something like we are about 50% certain that GW contributed, say, 2 to 5% of Katrina’s intensity.

    Then, of course, that additional 2-5% of intensity caused by GW would have done much more damage than the first 2-5% of intensity — it may have been the straw that broke the camel’s back or blew off someone’s roof, or demolished their home.

    [Response: The study you refer to about the European heat wave was also based not on analysing the single event, but on the statistics of such events in general. Basic idea: if GW has doubled the chance of such a heatwave, you could attribute half the casualties to GW in a statistical sense. Like rolling a six with the loaded dice, and if this earns you $100, attributing $50 to luck and $50 to the dice being loaded.
    But still your suggestion is a reasonable one, I think there is some scope for further study of Katrina. One could, for example, rerun the forecast models that computed Katrina’s development with half a degree cooler SST, say, as a rough-and-imperfect estimate of the potential impact of this extra warming. But ultimately I think studies like the one by Knutson et al. shown in Fig. 1 are more useful than working on a single case study where a lot of random chance is involved. – stefan]

  6. Heiko Gerhauser:

    What might be interesting would be to do simulations of Katrina’s strength, if SST had been 0.2 to 0.5 C lower.

    For judging the impact of past decisions on climate action in terms of their effect on Katrina, this constitutes a base line, the difference not ever having emitted any CO2 would have made.

    This could be expanded by looking at what difference recent decisions on climate change action would have made, such as for example signing onto Kyoto in 2000, followed by emissions reductions putting the signing nations onto a path to meet Kyoto.

    The result of that particular calculation is likely to come up with an effect equivalent to something like 0.0001 C, 0.001 mph in maximum wind speed or 0.001% in increased rain intensity or size, but it would be nice to see that beefed up a bit.

    Sometimes, the near term damage reduction potential from climate action is heavily oversold, when it should be clear that this is a long term issue with virtually all the pay-off of any action today and over the next two decades to be found later this century.

    In reply to Lynn, I’d also find it useful, if there was some focus on modelling the positive aspects of climate change. More deaths from heat waves can be modelled just as well as fewer deaths from extreme cold.

    While there is a good theoretical case for greater damage from tropical storms, there is evidence that mid latitude storms may have decreased in intensity compared to the Middle ages, and a good theoretical case that they should decline in intensity due to global warming.

    More carbon dioxide should mean more heat stress resistance in plants, as they shouldn’t have to breathe as hard to suck CO2 out of the air, and should mean higher yields. On the other hand, CO2 dissolving in the oceans would be expected to attack coral reefs.

    I think a balanced view requires looking at both the positive and negative impacts.

    I also know that the majority of economic models indicates relatively small net economic damage in 2100 (1-5% of global GDP), with a large fraction of that damage, in some modells virtually all the damage, concentrated in tropical nations.

    Not everything is easily measured in economic terms. Attempts to include the value of coral reefs or the stress on species forced to migrate or losing habitat, in the cost benefit analysis, do not lend themselves to consensus, as value decisions come into it.

    And even economics is much less of a hard science than climate studies.

    My own view on the economics is that a doubling of CO2 concentrations will have a small net positive effect, as I put greater faith in adaptation than I think is represented in the majority of economic models.

    [Response: You are right on one point: starting to implement climate protection measures in the year 2000 would have no measurable effect by 2005. And nobody has ever claimed it would – at least I have seen no such claim. But I have seen dozens of polemical statements like yours – that Kyoto makes only 0.001 ºC of difference by then etc. – written by people who do not want to take responsibility for the future consequences of their actions. This is a completely moot point. Kyoto or any other measures are not designed to make a difference within 5 years, which is obviously impossible given the timescales of the system. There is a world of difference, however, between having 2 ºC warming by 2100 (which is the policy goal of the European Union) or having 4 ºC or 5 ºC or even more warming then, and this is what we can decide.
    Concerning the European heat wave of 2003: it caused ~30,000 casualties and thus was the most severe natural desaster in European history. There have not been any cold spells or storms that have even remotely caused a similar number of casualties. Hence, there is no way a reduction in the number of cold spells could balance the lives lost in 2003. It does get very cold in Europe – e.g. in Norway. But this causes no desaster, because it has always been so cold, and people are adapted to it. The heat wave, on the other hand, was something unprecedented in human memory here, that’s why society was not prepared and it caused such a heavy toll.
    What I am trying to say: a warm climate is no worse than a cold climate. But large and rapid change is the problem, because new things happen that we and our infrastructure are not adapted to. Take sea level. Nothing is better about the current sea level, compared to a sea level three metres higher (a likely long-term outcome of unmitigated global warming). The only problem is that many of our cities are built near the current sea level.
    I’m afraid your optimism about net positive effects of climate change is quite unrealistic. -stefan]

  7. Steve Latham:

    Further to the comments by Heiko (#6) on the economics of [climate change-related] environmental catastrophes, at least from an economist’s perspective, but opposite my perspective on my own standard of living:

    From the article:
    J.P. Morgan senior economist Anthony Chan agrees that higher energy prices will curb both regional and national economic growth in the near-term.

    “I think a 0.2 percent decline in economic growth due Katrina’s impact on oil and the regional economy is a realistic assumption,” Chan said. Longer-term, Chan believes hurricanes tend to stimulate overall growth.

    Said Chan, “Preliminary estimates indicate 60 percent damage to downtown New Orleans. Plenty of cleanup work and rebuilding will follow in all the areas. That means over the next 12 months, there will be lots of job creation which is good for the economy.”

    Prof. Doug Woodward, with the Division of Research at the Moore School of Business at the University of South Carolina, has researched the economic impact of hurricanes.

    “On a personal level, the loss of life is tragic. But looking at the economic impact, our research shows that hurricanes tend to become god-given work projects,” Woodward said.

    Disasters are good for the economy, he said. Within six months, he expects to see a construction boom and job creation offset the short-term negatives such as loss of business activity, loss of wealth in the form of housing, infrastructure, agriculture and tourism revenue in the Gulf Coast states.

    In a note late Tuesday, Standard & Poor’s estimates that Katrina could “shave a few points off our forecast of 3.7 percent growth.”

    Among the industries affected, trade, tourism, agriculture, and construction (Florida’s largest industries), as well as Louisiana’s energy-related industries will be hurt in the third-quarter, the firm said.

    “At the same time, repairs to hurricane-related damage in Florida, Mississippi, Louisiana, and other regions affected by the storm should boost GDP in subsequent quarters,” S&P analysts wrote in the note.

    “Natural disasters bring in a lot of money from the outside to help in the rebuilding,” he said. “The rebuilding boom will generate incomes. Insurance money and federal relief money will pour in. This happened very quickly in Florida last year,” Woodward said. “Give it a year. We’ll see positive economy results maybe by the third-quarter of next year.”

  8. Steve Latham:

    I wish politicians would read RealClimate before making assertions such as this one!

  9. Stephan Harrison:

    Great article. However, you haven’t mentioned the increases in sea levels associated with climate change. On their own, aren’t they likely to increase the vulnerability of low-lying regions to storm events even if climate change has no impact upon storm severity or frequency?

  10. Lynn Vincentnathan:

    RE #7 & “hurricanes tend to stimulate overall growth” — that’s because “goods” and “bads” are lumped together. We could then claim toxic pollution in our water is a great stimulant to the growth of the medical industry (and it is), and, afterall, a human life is only worth about $10 in chemicals, so the net loss from those weaklings who die before they amass gigantic medical bills is not much (unless it’s your loved one).

    And GW shouldn’t affect our diamonds & gold very much, only those very cheap things like food.

  11. Roger Pielke Jr.:

    Guys- Overall a good article. One quick comment. You write that Emanuel’s study shows a trend in the “intrinsic destructive potential of hurricanes”. Isn’t an appropriate metric of “destructive potential” actual destruction? If the PDI is a good metric for understanding “destructiveness” (as it is in the title of Emanuel’s paper, which probably was chosen by Nature, not Emanuel), shouldn’t we expect to see some statistical correlation between the PDI (e.g., in the Atlantic) and actual measures of destruction (e.g., in the US) over a period of many decades? If this smells like a set up, it is. I’d urge caution in associating an abstract climate index, such as the PDI, with variables describing societal impacts, like destruction, until you’ve seen the science that demonstrates that such a linkage exists. Finally, for another perspective on hurricanes and global warming, pretty consistent with that written here, see:

    I’d be interested in hearing if (and where, exactly) any of the RC folks disagree with the review presented in this peer-reviewed paper. Thanks!

    [Response:Roger – I would presume that PDI is a statistically far more stable measure than actual destruction, which varies wildly according to the vagaries of the actual track, and other circumstances… had someone spent a bit more money on levees, Katrina’s actual damage would have been far less. This seems obvious: have I misunderstood your question? – William]

  12. Gerald Machnee:

    Re #5 & 6:
    I think too much emphasis is being placed on the fractions of a degree difference in SST and wondering whether a little change in temperature would have made a difference as well as wondering whether GW made Katrina stronger. If the temperature was the main determinant, then all the hurricanes should be Category 5 this year. Katrina was close to a “perfect storm” in that other factors such as moisture, stability and wind pattern were more significant in determining its strength. The Hurricane Center should be able to give a better idea what the main factors were. In addition it was made perfect by hitting the most vulnerable part of the “belly”. It could have caused flooding more rapidly by making landfall a little more westerly. The tragedy is that the authorities were not prepared in spite of indicating they planned 2 years ago.

  13. Heiko Gerhauser:

    “The discussion here is restricted to scientific topics and will not get involved in any political or economic implications of the science.”

    There is a lot of work covering the economics of climate change, as well as adapation and mitigation. You don’t seem to be covering these issues?

    Economics is a science, it’s certainly rather complex, as the misunderstandings of said science evident in comments #7 and #10 show.

    Without going into excruciating detail, economists are not saying that hurricanes are making us better off, or that there’d be no costs attributable to climate change, if GDP in the year 2100 were 99% composed of reconstructing housing after hurricanes.

  14. Steve Bloom:

    Re #11: The warm water does seem to be important. Remember that it’s a relatively late season development, so earlier hurricanes didn’t get the full impact. Also, Katrina’s path and speed resulted in it having what looks to be an unusual amount of dwell time in the upper Gulf. So, we should be able to see an obvious effect on other hurricanes that spend much time in that area. Probably it’s a good thing that hurricanes occurring much later than now tend to track into the Atlantic/East Coast.

  15. Stephen Berg:

    Re: #12,

    I do not think SSTs can be overemphasised, since it is from the seas that hurricanes obtain their energy. If SSTs were even an extra tenth (or even hundredth) of a degree warmer, it would increase the energy of the storm enough to increase the number of people killed and the damage done to property by the storm.

    Sure, wind shear and other factors play a part in the setup of these storms, but these other factors do not contribute much to the overall energy of the storm, at least not nearly to the extent that SSTs contribute.

  16. Steve Latham:

    Dear Heiko (#14 at this time),

    Thanks for not going into excruciating detail, but I’m curious about what you are suggesting I don’t understand (or Lynn for that matter). You posted statements that economics doesn’t account very well or objectively for various kinds of costs (e.g., damage to coral reefs, harm to tropical or poor countries, etc). I agreed and posted quotes from some real, working economists indicating that GDP (their usual metric) is positively stimulated by disasters. My comment was that those changes in GDP don’t correlate positively with changes in my quality of life. What am I missing?

  17. dusty:

    To me its simple and scary. More heat equals more powerful storms. In my heart, that little voice of truth says that more of this is to come. I have to note that I stay up late worrying for our future. The sad truth is we cannot really know the effects of higher sea surface temperatures other than to have proof that they provide a nice comfy atmosphere for more destructive storms. As a somewhat educated layperson trying to raise awareness in my own little corner of the net im starting to find that at least some denizens of this planet are waking up to this.

    We have so far to go though.

    Thank you for running this blog. God Bless. And keep it up!

  18. Eli Rabett:

    The current Landsea/Trenberth/Emanuel discussion has been parsed by many to mean that Landsea claims that the number of hurricanes is constant, and Trenberth is claiming that their intensity should increase as global warming heats the ocean surface. Emanuel appears to have constructed a figure of merit that confirms both sides of the furious agreement.

    However, there is a simple logical fallacy in this reconciliation. If we are talking about hurricanes and not just tropical disturbances, a certain proportion of tropical storms will move up to hurricane status if Trenberth is right, and that indeed is what Emanuel has shown. Therefore, at some point, either someone is eliding tropical storms into hurricanes or someone else is making a false statement.

    [Response:True, and one must be careful to say whether one refers to hurricanes (with windspeed above a certain threshold) or just tropical cyclones. -rasmus]

  19. wayne davidson:

    Katrina’s origins were so close to inhabited islands that it is likely an excellent hurricane to analyze. The relation with heat and destruction seems clear, with Andrew at the beginning of the then warmest year in history (1998), and Katrina at now what may surely be the warmest year in history for the Northern Hemisphere. Furiously destructive Hurricanes are not the only indicator of AGW, in context of those Hurricanes cycles in the past, or rather in contrast with past high intensity hurricane seasons, we now experience all time high temperatures raging everywhere in the world, 1 meter a day rainfalls, severe droughts on 4 distinct continents, many glaciers going or gone everywhere , and a good chunk of the Arctic Ocean permanent ice melted. Those just claiming that Katrina is part of a “normal” cycle, must somehow show that all these other distant but simultaneous temperature related changes have nothing to do with the Gulf of Mexico, or show that all other world wide warming cycles occurred at the same time as preceding Atlantic Multidecadal Oscillations, I doubt that “normal” cycle hurricane theorists can demonstrate that glaciers have melted to the extent that they have today, replenish themselves again only to achieve today’s all time low ice volumes. The problem is Global, the symptoms are local, and they vary according to highly individualized environments, however the common thread is Global Warming.

  20. joseph:

    Excuse me if I’m being simple-minded here, but before we apply all of this incredibly complicated, speculatory science to analyzing Katrina, doesn’t it make sense to compare it with the historical record. Any simple glance at Hurricane records show that this is not the first time in history such hurricanes have occured. 1931 was an incredibly destructive year. In 2000 there was not a single land-fall. There is little solid historical evidence that hurricanes are increasing in number or destructiveness. This seems more telling than uncertain infinitely complex computer models, I just believe we can’t let speculative science get in the way of more simple logic. If hurricanes like this have hit with some regularity in the past (which they have), is it not jumping the gun a little to slap down a global-warming tag on it. I am not denying global warming in anyway, just I think it is best to always check speculation with a little more sober look into fact.

    [Response: Have a look at Fig. 2 of the post – this is the sober data you want, not speculation. -stefan]

  21. Heiko Gerhauser:


    economists would not regard the quarterly changes in GDP discussed in the article as the most appropriate metric for judging the economic damage from a hurricane, in particular because GDP is a proxy for production, rather than assets.

    Economists do consider quality of life issues, though there is no consensus on how best to deal with them in cost benefit analyses.

  22. David Ball:

    As a severe weather meteorologist, I can’t stress enough how important articles like this are. Whenever extreme weather occurs, the public inevitably tries, on some level, to put the event into some type of global context. So a tornado touches down, devastating a community, or a hurricane like Katrina does the unthinkable and the inevitable questions come up: “is this El-Nino?”, “Is this global warming?”, “Is this normal?”, … All of these questions are valid and merit discussion, but the problem is that there is simply no way to answer them, short of a blithe, yes, these things are normal and as tragic as they are, they may happen again, and yes, there might be an impact from global warming or something else, but I can’t say exactly what they are.

    Having the folks at RealClimate present the current state of the science and basically state what we in the meteorology community already find on a day-to-day basis is very gratifying. Keep up the good work.

  23. Lynn Vincentnathan:

    RE #21, Okay, let’s take the Galveston cat 4? hurricane of 1900. Maybe some scientist could do a rough estimate of how much wmore intense it would have been with GW & the added increase in SST due to GW (though there might not be enough info on that hurricane).

    Another question:
    If hurricanes are to increase in intensity, then at some future point will we have to add another number, like category 6 (or are there constraints that make it beyond physical possibilities)?

  24. Pat Neuman:

    Regarding #11,

    Mr. Pielke, the referenced pdf shows an article in press (Dec. 2005) on Hurricanes and Global Warming, Bulletin of the American Meteorological Society. The authors shown in the article include yourself, the NOAA professionals listed below, and two others with the Tropical Prediction Center in Miami, FL.

    NOAA professionals:

    Christopher Landsea, Research Meteorologist
    NOAA AOML/Hurricane Research Division
    Miami, Florida

    Jim Laver, Director
    Climate Prediction Center
    NOAA/ National Weather Service
    National Centers for Environmental Predicion
    Camp Springs, Maryland


    Are the statements in the pdf article (Accepted 27 August 2005) in agreement with NOAA’s policy on climate change? Did Mr. John Mahoney of NOAA give his approval to the content of the article?

    One would hope that science articles would be judged on quality, rather than conformity with policy. Does NOAA even have a “policy” on climate change? – William]

  25. Heiko Gerhauser:

    Re 23

    What could also be done would be too look at all hurricanes making landfall in the 20th century, and then modelling the effect of 21st century sea water temperatures on them.

    In the 20th century 3 category 5 hurricanes made landfall in the United States, tripling that would mean 9 cat 5 hurricanes, but that should be the risk for year 2100 SST’s.

    So, maybe 6-7 cat 5 hurricanes in a business as usual scenario for the 21st century, and with concerted climate action over most of the 21st century, that could be reduced I guess by 1 landfalling cat 5 hurricane, which would be avoided, likely, sometime between 2050 and 2100 (and of course it would be nice to have that firmed up a bit, maybe including a glancing look at the near term effects of climate action to quantify how close to negligible they’d be).

    The 2100 cut-off is somewhat arbitrary, more cat 5 hurricanes could be avoided in the 22nd century, but also most of the climate action for that could occur late. It’s the big lag times in energy and climate systems, which, I think, make consideration of impacts 50-100 years out particularly appropriate.

  26. Mark Trexler:

    A great article. Stefan comments at one point:

    “What I am trying to say: a warm climate is no worse than a cold climate. But large and rapid change is the problem, because new things happen that we and our infrastructure are not adapted to.”

    This is a pivotal point. We frequently hear that “it used to be warmer and the dinosaurs liked it just fine.” That’s great, but we now have 6 billion humans hanging on to the planet, many pretty marginally. It’s not that a “warmed planet” will be “inferior” to today’s planet, but what happens to those 6 billion people during the transition?

  27. PHEaston:

    What is missing? Your article concludes with the very strong statements:

    “The current evidence strongly suggests that:
    (a) hurricanes tend to become more destructive as ocean temperatures rise, and
    (b) an unchecked rise in greenhouse gas concentrations will very likely increase ocean temperatures further, ultimately overwhelming any natural oscillations.”

    However, after carefully re-reading the article, I can’t see where this “evidence” comes from. The nearest to evidence for (a) might be your Figures 1 and 2. Figure 1 indicates that more CO2 will lead to an increase in hurricane intensity. However, this result is derived from a predictive computer model and not evidence. In any case, you state “this SUGGESTS that hurricanes MAY indeed become more destructive” – which clearly does not represent “strong evidence”.

    Figure 2 shows an apparent correlation between a “power dissipation index” (PDI) and North Atlantic SST. There is no explanation of what PDI is other than that it is “LIKELY a better measure of the destructive potential of the storms than previously used measures”. The term “likely” can not sensibly be transposed to “strong evidence”. From here we are led to the statement: “as tropical SSTs have increased in past decades, so has the intrinsic destructive potential of hurricanes”. A more convincing conclusion from the graph is that “as tropical SSTs have increased in past decades, so has the PDI”. It seems the reader is meant to have faith that an increase in PDI represents an increase in destructive potential, as no justification for this connection is presented.

    In relation to the findings of Emmanuel (2005), you state: “caution is always warranted with very new scientific results until they have been thoroughly discussed by the community and either supported or challenged by further analyses”. This is a sensible statement, but one that does not appear to correlate with your strong final conclusions.

    Conclusion (b) bears no relation to evidence presented in your article and appears to be based either on opinion or on the results of other studies not referred to or referenced here.

    Don’t assume I aim to discredit your conclusions. As a scientist, I just don’t see how they derive from the information provided in the article.

    [Response: Concerning (a) – there is a lot of evidence for hurricanes tending to become more destructive with increasing SST. E.g. the fact that they arise only over warm SST (>27 ºC) to begin with. Also, if you follow the hurricane forecasts of the National Hurricane Center on the web, you will see that SST is one of the key factors routinely used with every hurricane to forecast whether it will strengthen or weaken. E.g., on Friday, 26 August the 11.30 a.m. Katrina discussion read: “STEADY INTENSIFICATION TO NEAR CATEGORY FOUR STRENGTH BY 72 HOURS APPEARS TO BE IN ORDER GIVEN THE VERY WARM GULF WATERS BENEATH THE HURRICANE…” As you know, unfortunately this forecast was correct.
    Concerning the power dissipation index: this is the wind speed cubed, integrated over the surface area covered by the hurricane and over time. It is simply an integral measure of the strength of the hurricane. You could have also used the wind speed. But to a physicist, power dissipation is a more sensible measure, partly because there is conservation laws for energy (not for wind speed), and partly because any damage caused to structures is more closely related to the power transferred to them, rather than to wind speed itself.
    The evidence for conclusion (b) – that global warming will make SST warmer – was indeed not discussed in this post but in many others on our site. This is simply the standard evidence for rising CO2 concentration leading to global warming. You could turn to the IPCC reports if you are interested in this evidence, or e.g. to one of my own articles which summarises the evidence briefly at the outset. -stefan]

  28. Lynn Vincentnathan:

    An engineer, Dan, on another blog — — has put this forth (I edited it for brevity), & I think I did read about the thermohaline circulation slowing down somewhat. Could you RealClimate scientists comment on Dan’s points:

    “…GW affects the Gulf area in hurricane formation on 2 grounds. First there may be local heating and second higher latitude heating may help augment the decadal cycles being cited as the reason for the increased frequency. Both GW related aspects increase heat retention by the Gulf and therefore hurricane intensity.

    First,…the Gulf of Mexico…is very shallow with 38 percent of the ocean less than 20 meters deep. Because of this shallow depth, the earth’s heat imbalance can raise the temperature of this area faster and distribute that heat throughout the region.

    …I calculated that the earth’s heat imbalance of 0.85 W/m2…can raise the temperature of the first meter of ocean by a degree in about 2 months if all the heat was totally contained in that first meter.

    Since 20 meters is not a great depth, and if we assume the heat imbalance of 0.85 W/m2 went to heat just that shallow area, then it would take 2 years for the heat imbalance to raise the shallow ocean area an extra degree. The heat form the Gulf of Mexico is distributed world wide and even warms Europe. We are talking about the heat imbalance and if the long-term average flow rate of the current remained the same, then we would still have an imbalance with more heat being concentrated in the Gulf waters due to GW.

    Second, weather events concerning the decadal cycles which place us in a hurricane season I believe are due in part to GW if the thermohaline circulation is being reduced which would slow the Gulf Stream down (flow rate out) and therefore prevent the escape of heat from the Gulf region.

    …Increases in temperatures of the higher latitudes would also decrease density because warmer water is less dense. Since both ice melt and higher temperatures are happening, then density will be lower and this slows the Gulf Stream and adds to the decadal weather event which keeps more heat in the Gulf. In other words, the weather aspect of hurricanes is further aided by GW.

    I read where the heat influx out of the Gulf region has a magnitude of 1.4 billion megawatts. So, that heat has to go somewhere and evaporation is an easier way for this to happen than just the water increasing in temperature. So this heat energy goes into evaporation and mechanical energy in the form of a hurricane.

    …The Gulf of Mexico is one gigantic solar collector and the Gulf Stream is how the heat from that solar collector is distributed to Europe and elsewhere. Our distribution loop got clogged with low density water and we had a backup of heat until our heater over heated and blew off steam in the form evaporating ocean water which made a swirling cloud called a hurricane.

    Does this mean Europe will have a cooler winter if we have a strong hurricane season?

    I made many assumptions and I apologize to those who know more about the science. Nevertheless, I would love someone more qualified than I am with the science to add or subtract from what I said to add more clarity.

    If Dan is right on at least part of this, then are there perhaps other GW-induced factors that go into hurricanes, perhaps even go into the decadal cycle which goes into hurricanes, aside from SST? Of course, sea rise would make coastal land more vulnerable & hurricanes more destructive (I think “destructive” is a fine term for our anthropocentric focus here).

  29. Kirstin:

    Thank you. I appreciate this blog very much and I think you are doing a very good job.

  30. Pat Neuman:

    I think the term destructive power (footnote 1) could use more discussion.

    It was reported that Katrina was highly unusal for a combination of high intensity and large size.

    I would like to see Katrina ranked with hurricanes of the past according to size and total power. For example, Katrina’s size could be represented by the amount of land area (square miles) which experienced catgory 4 wind speeds. I would also like to see a scale that would include size and wind speed parameters, for ranking total power of hurricane for the U.S.

    My guess is that Katrina and Andrew were the most powerful, combined wind speed and size, hurricanes to hit the U.S. of the last three centuries, or longer.

  31. Roger Pielke Jr.:

    Re: #24. I had no contact with anyone in NOAA other than my co-authors, with whom I worked on this paper just like I would anyone else, irrespective of their employer. I doubt that NOAA has a policy on climate change, and I wouldn’t co-author a paper whose publication required approval by a government official. Hope this clarifies.

  32. Pat Neuman:

    Re: 31 Yes, that helps. Thank you.

  33. Jerry:


  34. Terry:

    It would help if you could explain a step in the logic of this piece.

    Higher temperatures mean higher energy levels, but in thermodynamics, it is the difference in temperatures that determines how much power a system outputs. For instance, a system with a heat sourec at 100 degrees and a heat sink at 50 degrees will produce more power than a system with a heat source at 120 degrees and a heat sink at 110 degrees even though the second system has higher temperatures.

    So, it would help me if you could explain the temperature difference that drives hurricane systems and how GW is expected to increase that temperature difference. (Or if I am wrong about this, explain why temperature differences are not important.)


    [Response: Much of the power for the hurricanes comes from latent heat: the condensation of atmospheric moisture as air parcels are raised. Warmer air leads to more moisture (roughly exponentially), so no T diff would be needed – William]

    [Response:The amount of latent heat release depends on details such as the water vapour concentration of the ascending air parcels coming in at the bottom of the storm and of those that emerge at the top. The amount of saturation water vapour is determined by the Calusius-Clapeyron equation (assuming local thermal equilibrium): e_s = 10^(11.40 – 2353/T), where T is the temperature in degrees Kelvin (absolute temperature). Freezing temperature (0C= 32F= 273.155K) produces a satiration vapour pressure of 611Pa. It is well known that the temperature diminishes rapidly with height (and the pressure drops as well, hence the need for a cabin-pressure system in airoplanes). The cold temperature you refer to, is to a large part determined by the height of the cloud tops in the hurricanes. Cold (T~ 210K) rarified air is not capable of holding much moisture, and a difference of a few degrees does not matter much there (T=210K -> 1.6Pa; T=220K -> 5.1Pa). A change in the temperature at the warm end, however, has a much stronger impact on the water content of the incoming air parcels ascended into the storm (T=295K -> 2653Pa; T=305K -> 4844Pa). (Besides, the air at surface level is more dense than aloft). -rasmus]

  35. Magnus:

    I just ran across this that says that there have bean no increase in hurricanes that comes in on the mainland of US. If I remember correctly I have read a statement somewhere that there have bean an increase of strong hurricanes over the Atlantic, do you have any numbers of that? And the reason why more havenâ??t struck US is it just pure luck?

  36. Almuth Ernsting:

    Re 5:
    I think a study that looks at the probability of Hurricane Katrina having had the same destructive potential with, say, 0.5 degree C cooler SSTs would be really great. I agree with Stefan’s response that looking at the future is far more important – the future, after all, is the reason for reducing emissions now. When I look at reports in the media, and public perception in general,however, any evidence that global warming is real and is already making extreme weather and, hence, terrible suffering more likely today is far, far more powerful than the most terrifying prediction for 2100. The Hadley Centre study on the European heat wave was widely reported and I am sure changed some people’s minds. Public polls show that most people in the UK (and US?) accept that climate change will threaten future generations, but most are in denial about it affecting their lives, and people’s willingness to take action is directly linked to whether they think climate change will affect their own generation.

    Re 6:
    Heiko Gerhauser states in 6 that mid-latitude storms may have decreased since the middle ages and could be expected to decline with global warming. I don’t know about trends since the Middle Ages. I do know that British storms have doubled over 50 years, according to the Hadley Centre [see: Hadley Centre climate forecasts are for more high-intensity storms in Britain as global warming intensifies – Scotland has just had the strongest storm in living memory this January, which subsequently hit Scandinavia after increasing its wind-speeds over the North Sea (so it’s not just us, it seems).

    [Response: Does climate change only affect “future generations”? I am middle-aged and expect to still be around in 2050. And the life expectancy of children born today goes beyond 2100. “Future generations” sounds abstract – but climate change will strongly affect the lives of my generation and of our children. And most people care a lot about the kind of future their children will have. -stefan]

  37. Heiko Gerhauser:

    Re 36

    I suppose this thread shows again how difficult it is to keep politics out of the discussion (“politics” in this context = preferences for how climate change should be dealt with, and a consequent desire to present information in a way to sway the public towards that preference).

    The probability calculation Almuth proposes is tailor made for influencing the public towards “greater” action, while a calculation that looked at say the impact of Kyoto in 2020 on the wind speed of a second Katrina, compared that to the variability introduced by natural cycles and emphasised that this was based on models, while there had been no conclusive trend in tropical cyclone wind speeds so far, would be made with a different kind of advocacy in mind (Pielke et al’s paper is very clearly going in this direction).

    One measure makes the impact of climate change action look near term, large and certain, while the other emphasises how small, far out in the future and uncertain the benefits of any climate change action would be.

    On British storms, the link is messed up, because of the bracket at the end, just in case anybody else has trouble with it.

    Maybe the climate experts on this site could address the subject of mid latitude storms in a bit more detail.

    I gather that the main reason to expect them to decline is the lower pole-equator temperature difference that climate change would bring with it, and that this is the main driving force for mid-latitude storms, while SST are the most important variable for tropical storms.

    IPCC in their 2001 report mention pressure changes, as does the Hadley Centre, but I am not clear whether this amounts to merely a shifting around of where stronger storms occur, or a sufficient case to argue that the competing effect of the lower pole-equator temperature difference would be overcome.

    Re 6

    I know that the true argument for acting relates to what’ll happen beyond 2050, and that said action must be continued through much of the 21st century to have much effect, and you say this clearly.

    But, there are plenty of people who do not realise this, and when they watch a certain recently released movie on the subject, or hear about the German environment minister linking Kyoto and Katrina, they are easily misled into thinking otherwise.

    Current climate disasters are much better for convincing the public than projections, though they shouldn’t be.

    I know that the “Kyoto will only do so little” argument can be stretched too far, to the point of suggesting climate action won’t do anything in any case, and I do see your viewpoint there (though I think you do needlessly brush an ad hominem in the process of stating that viewpoint).

    But, you also know that whenever a major climate related disaster happens, the media will ask scientists whether it’s related to global warming, and that these disasters will be used to justify Kyoto, and that the immediacy of the benefit can easily be overstressed to the point where many people do believe that Bush’s refusal to sign Kyoto directly caused Katrina or at least made it noticeably worse.

    I think it is entirely appropriate to address that misconception.

    On your other point, I know that a major issue is how well and quickly we can adapt to the changing climate. As you say it makes little difference whether sea level is 3 m higher or lower, but if cities are built next to the present shore line, adaptation has a cost.

    I just don’t share your opinion that the cost of adaptation would be high enough to off-set the benefits, or at least to off-set them by enough that much climate change action now is a good investment.

    As you don’t include the economics of climate change on your site, I think we can leave it at that difference of opinion without having to sling insults suggesting lower motives.

    I also happen to disagree on the specific example of adaptation you chose to highlight.

    High summer temperatures are exceedingly easy to adapt to nowadays, which is why people are so happy to move to the South of the US, or to take a summer holiday in Spain. Climate change so far is equivalent to something like moving 100 km South in terms of maximum summer temperatures, with decades to adapt.

    The way to deal with this is air conditioning. That works near immediately, and is useful also in the present climate, though it is energy intensive and therefore currently contributes to CO2 emissions.

    I’d bet that the death toll estimate is based on a year on year comparison and mostly relates to elderly people already close to death. To claim that the increase in summer maximum temperatures in Europe is too rapid for adaptation, and therefore responsible for increased death, is a very weak argument, much, much weaker than that sea level rise will be too rapid for adaptation to have low costs.

    [Response: Quick response to two of your points.
    First, what the german environment minister actually wrote in his much-villified article published on Tuesday 30th was very much down the line of our post. He wrote that no individual storm can directly be linked to global warming, but that climate change is making extreme events more likely. He used this to argue for climate protection measures, finishing his article by stating that the international community should stretch out their hands to the US with a proposal for the future of an international climate policy.
    Second, you state that the casualties from the European heat wave were mostly “elderly people already close to death”. Nice one. And as you will know, another standard skeptics argument. Why not check the facts, before you publish such claims on the web? In France, the mortality rate during the heat wave was statistically significantly increased in all age groups above 45 (my age). See Schär and Jendritzky, Nature 2004. -stefan]

  38. Stephen Berg:

    A paper examining the increase in temperature of the world’s oceans over the last 50 years or so:

    (I figured that it could be a benefit for the discussion on this thread.)

  39. Lee A. Arnold:

    With regard to the economic cost-benefit analyses of global warming, or of a climate treaty to brake it, it should be pointed out that economists must ignore the alternate new pathways that the economy will doubtless take under the vibrancy of capitalism, because these do not presently exist. And in the other column, they also also ignore the nonmonetized ecosystem services (clean water, clean air, disease suppression, etc.) provided to us by nature right now. We can’t even predict the present economy with much certainty, so coming up with cost-benefits under the new conditions, while a valuable academic exercise, is almost certainly useless. You can argue that Katrina is likely to stimulate the GDP through rebuilding, and that would be true, but so what. This is an old schoolyard truism usually known as the “broken-window argument”: go break a window, raise the GDP. You are not increasing the total welfare, only getting it back to what it was. And of course not tallying the incalculable suffering of the meantime. We may never know whether Katrina is attributable to warming, but the politics of it is clear: it is of the magnitude which might be imagined in a climate catastrophe. Anyone who doesn’t take pause at this, should be put under the sober care of a qualified psychiatrist. (I offer this last remark, of course, as a strictly scientific observation.)

  40. Isaac Held:

    With regard to Williams answer to Terry (#34), I believe that Terry is correct that it is temperature differences that are fundamental, and not, for the most part, the temperature itself, as Emanuel has discussed in a series of important papers on the maximum intensity that hurricanes can attain. It is the temperature difference between the ocean surface and that of the upper level outflow that is crucial. From this perspective one can see that the issue of hurricane intensity is linked with that of trends in upper tropospheric temperatures. We should all hope that the models and data analyses which suggest that the tropics stays very close to a moist adiabat as it warms are correct. If not, and the upper troposphere warms less rapidly than the surface, the temperature difference relevant for hurricane strength will increase that much faster.

    [Response: This is an interesting point, which deserves better discussion that I can do. I’m sticking with my view for the moment, bolstered by the fact that everyone seems to correlate hurricanes against SST and I’ve never seen anyone correlating them against upper temps. I’m not sure which KE papers you mean. In he says “everywhere we have looked, the change in hurricane energy consumption follows very closely the change in tropical sea surface temperature” – William]

  41. James B. Stephens:

    The solution is to tax large gas-hog vehicles that do not deliver things to our industrial systems. The tax should be related to the miles per gallon of the vehicle. It should be a non-linear tax. I drove a 25 HP VW as my first car. I had to draft Greyhound busses to get to 65MPH. I made friends with the drivers, and they stopped turning off a bank of their spark plugs and producing a large back fire to get me to stop drafting them. We need to incentives more efficient means of transportation. We need to provide safe lanes for Bicycles users. We need to provide lanes for small efficient vehicles. China and India are making efficient 2,3 & 4 wheel means of travel.
    Many employees and their employers should be incentivized to allow them to communicate to work. Home owners should be allowed to have production machines in their own homes. Schools should be incenivized to allow students to communicate to school. Travel waste time and wealth. The internet moves at the speed of light and costs only a few cents per gigabit of information that is transferred.
    Let me know what you think.

  42. James B. Stephens:

    We should incentivise every one to save energy by communicating to work over the internet if they can. Companies should allow workers to make things in their homes or to live near their place of work. Commuters see many other workers going the other way on their commutes to work. Incentivise them to exchange their homes. Tax the gas hog vehicles off the roads.

  43. John Q. P.:

    Just a brief note: Great site; finally a quality resource for those who debate the professional naysayers (such as those found on sci.environment). Keep up the good work.

  44. Pascal:

    I’m not completely agree with the William’s response to #34.
    The vapour latent heat remains latent if you haven’t a cold sink.
    I think that, for mid’s latitudes storms, this cold sink is given by polar air masses.
    With GW there is a reduction of T gradient between equator and poles , so this types of storms should be diminished.
    For a hurricane it’s not the same phenomenon.
    The cold sink is the upper troposhere (by radiative loss to space).
    The condensation of vapour in this cold sink gives more energy to the hurricane.
    With GW the T gradient between lower an upper troposphere will be more important than to day.
    Maybe it’s an explanation, with SST increasing, to the future average strength of hurricanes.

  45. Steve Bloom:

    Kerry Emanuel has a freshly-updated page on his MIT site explaining his findings in some detail: . There’s also a public-access link to his Nature letter and supplementary material.

    Re #s 34 and 40: I would appreciate some additional information on this.

    [Response: So would I. Thanks for the KE link – useful. I’ve written this, which doesn’t appear here because its only my speculation – William]

  46. Roger Pielke Jr.:

    Re: 37. Here is how we conclude our BAMS paper: “But a great irony here is that invoking the modulation of future hurricanes to justify energy policies to mitigate climate change may prove counterproductive. Not only does this provide a great opening for criticism of the underlying scientific reasoning, it leads to advocacy of policies that simply will not be effective with respect to addressing future hurricane impacts. There are much, much better ways to deal with the threat of hurricanes than with energy policies (e.g., Pielke and Pielke 1997). There are also much, much better ways to justify climate mitigation policies than with hurricanes (e.g., Rayner 2004).”

  47. Roger Pielke, Jr.:

    Guys- I’m going to be a bother and follow up on the request in #11. After reading your post, Kerry Emanuel’s website I feel strongly that there is a strong consensus on hurricanes and global warming in the scientific community (in spite of media reports and advocacy statements to the contrary). It would therefore be useful to your readers and other observers, and scientifically productive to the community, if you would offer your comments on our peer-reviewed reviewed paper forthcoming in BAMS. Are there conclusions ior intermpretations in that paper that you would disagree with? Overlooked literature that would change the conclusions? If so what specifically are then points of disagreement and on what basis would you disagree? Science advances by engaging each other in the open. I’ll have to admit some disappointment that you’ve written two reviews of this topic without acknowledging that this peer-reviewed paper exists. So here I am bothering you again. If we are wrong in important respects, then let us know! Thanks. Here again is the link:

    [Response: Roger, Speaking for myself, I agree with much of what is contained within your paper, as I also agreed with much of what Trenberth said when this issue surfaced earlier this year. Yet much of the commentary at the time and now has focussed on rather semantic interpretations of what words like ‘linked’, ‘connected’ or ‘significant’ mean. Some people have assumed that they mean ‘directly caused by’ and have then set up a straw man of specific attributions which are easy to criticise. There is no fundamental contradiction between the potential connections in a statistical sense discussed here between GW and hurricanes and your statements regarding the causes of accelarating cost of such disasters and their (limited, and possibly counter-productive) relevance for moving the GHG-emission control issue forward in the policy realm. Such connections may not be ‘significant’ in an economic impact sense (which is how I parse your paper), but may well prove to be significant in a purely physical climatic sense. Thus I don’t agree that it is ‘premature’ to discuss such links, despite the fact that these links are not the first order control on hurricane damage. It should be possible to discuss such issues without immediately having those discussions projected onto the highly politicized debate concerning approrpiate policy responses. -gavin]

    [Response:Roger, I am glad you see a consensus. Do you know that Goldenberg and yourself are the two scientific witnesses cited by the german news magazine Der Spiegel yesterday under the headline that the increase in hurricane activity “has nothing to do with global warming”? This definite conclusion is directly associated with a quote from you in the text. I know how the media often distort, and I don’t know what you told them, but perhaps this calls for a letter from you to correct this?
    Concerning your disappointment for not being cited: remember your paper is not yet published. We cannot always be aware of all forthcoming papers – and even if we are, we often wait with citing them until they are published.

  48. Heiko Gerhauser:

    Re 37

    I didn’t comment on what Trittin actually said or didn’t say, but merely on the need to correct a misperception among members of the public. I’ll leave assignment of who’s to blame for that misperception to others.

    My institution doesn’t have an on-line subscription to Nature, I expected the kind of finding you cite and it doesn’t contradict what I said.

    Re 45

    Kerry Emanuel’s page is excellent, and adds considerably to the article published above, I particularly liked FAQ number 9, as a succinct summary of the science.

  49. Roger Pielke, Jr.:

    Re: Gavin’s reponse to #47

    Thanks much Gavin for these comments. Just a few reactions.

    1. We (you and our BAMS paper) seem to be in violent agreement about the possibility of global warming resulting in a demonstrable, statistical influence on the behavior of hurricanes. I also think that Trenberth’s paper is consistent, and Emanuel as well — hence my claims for consensus on this issue.

    2. We didn’t say that it was “premature to discuss such links” but rather we stated “claims of linkages between global warming and hurricane impacts are premature for three reasons.” What we mean by premature is that there is no evidence in the literature to support a claim that global warming has resulted in demonstrable effects on hurricane impacts, whether they are measured in terms of economics or otherwise. As we state, Emanuel’s paper is suggestive of a linkage with the observed behavior of storms, but effects have not been observed in the impact record. Additional research, we note, may yet overturn this conclusion.

    3. You write, “It should be possible to discuss such issues without immediately having those discussions projected onto the highly politicized debate concerning approrpiate policy responses.” In an ideal world this might be this case, but that is not our world. The reactions to Katrina in over the past week illustrate that any statement by scientists on hurricanes and global warming carries with it political significance. We need to accept this and discuss our science accordingly (i.e., we need to carefully place the science into policy context). And of course we’ve discussed this before.


    [Response: “…but effects have not been observed in the impact record”. I recommend Kerry Emanuel’s consideration of why this is the case. He writes: “the data of landfalling hurricanes in the U.S. is less than a tenth of a percent of the data for global hurricanes over their whole lifetimes”, and shows that from such a small subset of data and given the amount of natural variability, there is no way you would be able to detect a trend by now. To get enough signal/noise to detect a trend, you need to consider all hurricane data, not just those landfalling in the US. -stefan]

  50. Lynn Vincentnathan:

    RE #37, GW actions have many many other immediate & future benefits: they prevent/reduce many other environmental harms (local air pollution, acid rain, ground & water pollution, etc.), they are good for the health (e.g., cycling & walking), they reduce crime (cycling, walking), they reduce our implication in foreign conflicts & tax money to protect oil supplies, they save money without lowering productivity (even increasing it), they save businesses from folding & households from going into hock. We should be doing these (which I have mentioned in earlier posts under other topics on RealClimate), even without GW, but it was the idea of my GW contributions to African droughts that first moved me to start down this wonderful, healthful, money-saving, living standard raising path. NO REGRETS. With 100% wind energy from Green Mountain, we have now reduced our GHGs more than 1/2, maybe more than 3/4 from our 1990 emissions (also counting water & products, which entail GHGs in their production).

    I would hope Katrina would inspire others to start down that wonderful path, even if doing so doesn’t have a big impact on reducing future Katrinas.

  51. James Annan:

    Roger says (#49):

    we stated “claims of linkages between global warming and hurricane impacts are premature for three reasons.” What we mean by premature is that there is no evidence in the literature to support a claim that global warming has resulted in demonstrable effects on hurricane impacts

    Ah, that makes things clearer. I had previously read your statement as meaning that any claims of a linkage between global warming and future hurricane impacts was premature given the current level of understanding. If you are only referring to the attribution of past (current) impacts, then it seems much less contentious.

  52. Pat Neuman:

    Some questions:
    Did Katrina have an unusually large area (diameter)?
    Is the average size (diameter) of hurricanes increasing?
    Should hurricanes in the future be larger due to global warming?
    What effect should an increased tropopause height have on hurricanes?

  53. Roger Pielke Jr.:

    Re: #51. James- Yes.

  54. Joseph O'Sullivan:

    This was a very informative post. RC is doing a good job of providing information on current topics that are big in the news and replying to reader�s comments. The connection between climate change and hurricanes is a very appropriate discussion topic.

    Popularizing climate change science is a worthwhile undertaking. IMO when science has political implications, popularizing science becomes very important. A source of accurate scientific information is highly valuable so people can learn about the science and hopefully better understand the political issues. Its good to see that RC does not stay away from controversial scientific topics that might draw some negative attention from those who are concerned about the policy questions that revolve around the science.

    As far as rising ocean temperatures are concerned, I know studies (like Barnett et al 2005) demonstrated there is an anthropogenic signal (if I am using the term correctly, meaning a discernable increase in ocean temperature that is due to human activities) globally. I wonder how the level anthropogenic warming varies in different parts of the oceans and how this affects TCs.

    There are groups that are helping Katrina victims. Help if you can.

  55. wayne davidson:

    The link between heat and Hurricane intensity is unquestionable, as atmospheric water vapour density increases with higher temperatures, the energy source is likewise augmented, same goes for cyclones. Ever heard of a dry cyclone? Again stronger cyclonic activity is also found everywhere in the world, including in the Arctic, currently experiencing greater open water, with one Canadian High Arctic storm generating winds in excess of 115 KPH last winter (very uncommon), a precursor, one may say of Katrina and others. The logic is simple and is applicable worldwide. The point of view that Global Warming can’t trigger greater Hurricanes is a weak argument yet to be explained with clear words, but of course it is brought out to discredit that there is any Global Warming in the first place.

  56. Michael Jankowski:


    Could someone do it theoretically? Well, they could try to correlate AGW to SST to hurricane strength and come up with a number. But what about all the other factors? If AGW is real and influential, couldn’t that have had something to do with the path that hurricanes take? Should AGW sometimes get credit for pushing a hurricane away from Miami, New Orleans, Houston, etc, and towards unpopulated areas (or just back out over the Atlantic)?

    We have a decent grasp of forecasting tropical storm and hurricane paths a few days in advance. But I don’t think we can model what Katrina or any other hurricane would’ve done without the existence of AGW to any degree of accuracy.

    Look at it this way: you’re on a road trip across Texas. You’re a safe driver and are trying to save on gas, so you drive 45 mph. But at some point several hours into your trip, you fall asleep at the wheel, drive off the road, and hit a tree. You escape with just a broken arm and some bruises think to yourself, “Thank goodness I was only driving 45 mph instead of 55, 65, or 70!” But then you realize that had you been driving 55, 65, or 70 (or whatever speed) the whole trip, you would’ve reached your destination and therefore never fallen asleep at the wheel. Or if you had averaged just 0.001 mph faster the whole trip, you would’ve been further up the road and driven relatively harmlessly into an open field rather than hitting a tree and injuring yourself.

    Looking at Katrina from birth to landfall, it seems to me that any significant AGW could have had a number of influences along the way. I think it’s a drastic oversimplication to try to attribute x% of the damage of a hurricane to AGW.

  57. Phillip Olsen:

    I used to not think humans had much to do with Global Warming, but then I zoomed in ( on these satellite images of 785 U.S. facilities that emitted more that 100,000 tons of CO2 during 2004. Some of these locations released more than 20M tons during one year.

    The web site takes a few seconds to load, but once it loads, the speed is fast as you click on the icons in the right-hand column and the map zooms in and gives you a satellite image of these smoke stacks.

  58. Lynn Vincentnathan:

    RE # 34 & 40, something strange (according to our local weatherman) happened when Hurricane Emily came to us (its eye was about 70-80 miles south of us): There were lots of large hailstones that came down around Brownsville, TX. Our weatherman said he was unaware that had ever happened in our area during a hurricane. Seems that would perhaps indicate some interesting or extreme temperature difference was involved.

    Now, I just saw “Day After Tomorrow” again (for a paper I’m writing on fictional accounts of GW), and it featured deadly hailstones raining down on Tokyo & elsewhere. I know the science was pretty much trumped up on the film, but maybe there’s something beyond normal expectations in the Emily hailstones, maybe a hint of some GW phenomenon, or maybe this is all just quite normal/natural.

    [Response:The ‘science’ in “Day After Tomorrow” was plainly wrong: for starters, it would be impossible for a downsurge of air aloft on that scale, and such thin air would not be able to freeze the ground which in comparison has an enormous heat capacity (it would take time for the heat to drain away…). Furthermore, for thin air high in the atmosphere to ‘fall’ down to the ground, you would need to create a region with near vacuum conditions (people would suffocate and ‘explode’ because of lowered pressure, rather than freeze to death). In other words, it contained some very silly aspects. Even the several-degree cooling of the currents off Greenland while still being open sea, would be impossible, since the temperatures here are just above freezing anyway (the waters first would have to freeze, which would require extra release of heat due to phase change) and then the ice would have to freeze further (you would also take into account heat conduction in ice…). The aspect about hail storms, could be some of the more realistic part of the film, though, but – personally – I would say that this film is purely entertainment (as well as being a critique of politics?) and shouldn’t be drawn into scientific debates. -rasmus. P.S. a descent – air sinking – will lead to a compression of the air in the real world, which would again warm the air. The storm surges also constituted to some of the very unrealistic features of the film…]

  59. Eli Rabett:

    RE 56. Or you could have hit the tree at 70 and died, and killed your wife and kids. Sort of like NO. Care to tell us the advantages of faster winds in hurricanes for those of us on the ground?

  60. Heiko Gerhauser:

    Re 47

    I could find no such headline on the site of Der Spiegel. Could you provide a link?

    There is a an article though quoting the chancelloer as saying that Katrina should have consequences for energy policy.,1518,373480,00.html

    I am not a climate scientist, just a chemical engineer working on renewable energy.

    I do think that there is a broad consensus that there likely is an effect from increased SST, but that so far it is not sufficiently significant to be visible in the impact record, while lots of other things are, including the well known natural decadal cycles affecting hurricanes, flood defenses and increasing population and property values.

    Roger also points out on his site that it is not just SST that are affected by climate change, I read this to mean that land use changes, local changes in climate forcings and so forth may counteract the expected increase from SST locally.

    Which I take to mean that it is possible that the overall increase consists of a few decreases and many more increases. If that’s the case, it’s not just that landfalling hurricanes occur rarely and therefore statistical power to see a trend is poor, but that for US landfalling hurricanes there truely may be no net effect from global warming so far (I don’t think whether a consensus on the likelihood of that is possible, I guess it would be of the order of 10%).

    Finally, I think what the media really want to know when they ask about Katrina and global warming is whether the connection is “significant”, and I don’t think there’s consensus there, partly as Gavin says, that’s a matter of semantics, partly it’s a genuine disagreement as to how important global warming is where hurricanes are concerned compared to other factors, and how “significant” an argument the influence of global warming on hurricanes is for deciding energy policy.

  61. Almuth Ernsting:

    Further to my posting [35] – sorry about the web-link regarding increasing storms over the UK. I hope this one works better (and gives more details, too):,3604,1103539,00.html

    I completely agree with Stefan – I cannot understand at all why people think that climate change would only affect future generations (which, for many of us are our children anyway). I, too, hope to be around by 2050, and when I see nature and wildlife around me change and diminish at rapid speed right where I live and already now, then I don’t know if “hope” is the right word. I found this good summary of people’s perception that climate change is real but will not affect them personally:

    It is one of the reports submitted to the climate stabilisation conference in Exeter this February, and it gives a link to the most recent public poll results. It makes it clear that people see climate change as some vague threat, rather than relating it to any specific impact that they can see. When I read the media insisting that hurricane Katrina, or the Spanish drought, or repeat flooding in the UK and Central Europe are part of a normal cycle and cannot be linked to global warming, then I can vaguely understand where those believes come from.

    Re 37:
    Heiko repeatedly equates Kyoto with action on climate change. I am quite aware that this web-blog does not comment on different policy approaches. But we must not use Kyoto a synoymous with ANY action on climate change! Yes, we can all wonder what Kyoto could have achieved, but then we can also all wonder where we would be if the world had adopted a Dutch proposal in 1989 to slash CO2 emissions by 20% at that time, with further cuts to follow. Or we can look at the TAR emissions scenarios or the papers about stabilising the atmosphere at the 2005 Stabilsation Conference instead. And if you are not sure about the benefits of mitigation – I recently went to a talk by an Indian scientist who spoke about the melting Himalayan glaciers and his fear that, if we don’t stabilise the atmosphere, they will go and stop feeding those major rivers that provide water and make agriculture possible for 1-2 billion people. Saving those people must be a pretty big benefit, no matter what costs you calculate.

  62. Roger Pielke Jr.:

    Re: 60 On hurricanes and SSTs, I am simply repeating what I hear from the hurricane experts, e.g., Emanuel (2005) writes, “only part of the observed increase in tropical cyclone power dissipation is directly due to increased SST.” I am not suggesting anything more (not my specialty).

    Look for a very significant paper by Webster et al. coming out in Science that adds considerable nuance and important data to this discussion. It has some interesting data and is consistent with Trenberth (2005), Emanuel (2005) and Pielke et al. (2005). If you focus on recent peer-reviewed studies, rather than quotes in the media, there is a clear consensus on hurricanes and global warming among the scientific community, despite characiatures to the contrary. The debate, such as it is, appears in strident statements made to the media by some scientists (e.g., Trenberth, Gray) and scientifically-incorrect assertions by political advocates (e.g., in connecting Katrina with global warming OR assertions that global warming can have no effect on hurricanes). The reality is more subtle, and the implications for policy more pedestrian.

  63. Michael Jankowski:

    If you’d been driving 70, you wouldn’t have fallen asleep at that spot, hence you couldn’t have hit that tree. It doesn’t mean you wouldn’t have hit another tree somewhere else (except for the fact that in my example, you would reach your destination prior to falling asleep and that therefore never would’ve fallen asleep and had an accident). The point is that just equating AGW to % destructiveness based on the theoretical increase in wind speed is a major oversimplification.

    If you want to relate that analogy to New Orleans: it would be more like knowing full-well you were likely to have a serious accident on your trip but not bothering to tell the wife and kids to put their seat belts on until right before the accident when it’s too late, then being unable to administer life-saving first aid to your dying wife and children because you threw your kit out the window a few minutes earlier (you counted on the ambulance and hospital to fix everything).

    I never said there were advantages to higher wind speeds in hurricanes, simply that it seems to me that significant AGW would affect more than wind speeds. For example: which would be worse: (1) Category 4 Katrina hitting landfall just east of New Orleans, (2) a Category 5 Katrina never making landfall, (3) a Category 5 Katrina hitting the FL panhandle or (4) a Category 5 Katrina hitting southern TX? Case #2 is obviously the best, and I would argue that Cases #3 and #4 would have far less devastating effects than what #1 did. So the worst case scenario in my example is actually the weakest hurricane. And it seems to me that AGW, if it is that real and significant to hurricane wind speeds and SSTs, could produce significant changes in hurricane paths. That could be generally good (less landfalls), generally bad (more landfalls), or simply a case-by-case basis. I’m no hurricane expert, and I don’t know if there’s anything out there on the relation of hurricane paths to GW/AGW/SSTs/etc. I just find it hard to believe that the path would’ve been identical in a significantly warmer (or cooler) world. If – and it’s a big if – we get higher wind speeds but far fewer landfalls, couldn’t that be a good thing? Obviously, higher wind speeds and the same/more landfalls is a bad thing. Is there any such modeling or studies out there on the subject?

  64. Pat Neuman:


    In your article [Pielke et al. (2005), Hurricanes and Global Warming], it states:

    … “it is exceedingly unlikely that scientists will identify large changes in historical storm behavior that have significant societal implications, though scientists may identify discernable changes in storm behavior.” …

    Earlier, I asked realclimate if the average size (diameter) of hurricanes is increasing? I think an increase in the size of hurricanes would be a change which would have significant societal implications. Do you agree?

    Another point made in your article: “The views expressed are those of the authors, and for the four co-authors employed by the U.S. government, do not necessarily represent those of the National Oceanic and Atmospheric Administration.” And earlier in realclimate you wrote: … “I doubt that NOAA has a policy on climate change, and I wouldn’t co-author a paper whose publication required approval by a government official.”

    For me, will you ask your co-authors with NOAA if the article was discussed and given a go-ahead by those up their chain of command?


  65. David Adamson:

    I appreciate your thoughtful and science-based debunking of obfuscators like Steven Milloy. His work strikes me as dangerous and pernicious in the extreme. Bravo to the scientists on this site who are taking on the corporate apologist who themselves masquerade as debunkers of junk science in order to push their political and economic agendas.

  66. Lynn Vincentnathan:

    RE response in #58, I know DAT was way off scientifically. My main question had to do with the large hailstones that actually came down during Emily. I wouldn’t be asking, but our weatherman said he had never heard of that happening before, so I was wondering if they might at all be related to any GW phenomenon, or perhaps contrary to GW science, or just normal.

  67. Steve Bloom:

    Re #66: Lynn, this is more of a weather question than a climate question, so I’ll take a stab at it based on my sole qualification as a former resident of tornado alley. Generally, there are numerous reports of tornados and thunderstorm activity associated with hurricanes. Hail is intimately associated with thunderstorm activity. What surprises me is that your weatherman would have been surprised by this. Is thunderstorm-associated hail (actually the only kind I’m aware of) not common near Brownsville? I wonder if he was talking about hail closer to the center of Emily, which for all I know might be unusual. My memory of basic meteorology is that thunderstorms require hot and cold air masses to form, which I suppose would cause hail to not be expected very near the eye of a hurricane even if the hurricane was pushing into a cold air mass. Finally, I doubt that the size of the hailstones is very meaningful since large hail could be expected from energetic thunderstorms and hurricane-associated thunderstorms should be on the energetic side.

  68. wayne davidson:

    Have not heard it yet… Is good to say that GW has no or very little effect on Hurricanes, but would appreciate an explanation….. That would be better. Contradicting simple atmospheric physics demands no less; like world wide increase in water vapour density triggered by greater SST’s and plain warmer air causations. Proposing it has no effect on cyclones, rings like a slogan not science. An explanation aside from vague unimpressive assertions would be appreciated. Hurricanes are not that dissimilar to cyclones (they die as typical cyclones), so lets say that you are not an expert on hurricanes, then you may have an opinion on lesser meteorological entities? The question is simple: does warmer moist air create stronger cyclones? I rather think the answer is positive, and that answers about GW questions are simple, just like the meaning of glaciers disappearing everywhere.

  69. Roger Pielke Jr.:

    Pat- (#64)

    1. A change in the size of storms, just like changes in frequency or various measures of intensity could certainly have societal implications. The question is whether we can observe the effects of changes in the behavior of storms in the impacts record (e.g., we do see pronounced differences in impacts according to the phase of ENSO, El Nino/La Nina). So far, we haven’t seen evidence of significant changes in the impacts record. We may see them in the future, but not yet.

    2. I can tell you definatively that our paper was not subject to any approval up the “chain of command.” Though we should be so lucky that the views expressed would be reflected as official policies ;-) Again, our paper is consistent with Emanuel (2005) and Trenberth (2005) and a new study soon to be published. The “debate” over this issue exists only in media statements and advocacy efforts, and not in the peer-reviewed literature. Clearly, Gray and Trenberth, for example, have different expectations about what future research will show, but until that research is conducted and published, I think our paper is an accurate assessment of the current state of knowledge on this topic as reflected in the literature. Sooner or later it will be out of date, as new work is published, and then it’ll be time for an updated assessment.

  70. Pat Neuman:

    1. Francis (2004) and Katrina (2005) were unusually large, right? Does anyone know of plans to study what goes into determining the diameter of hurricanes, and if size has increased on average recently? We won’t see any evidence of change unless we study this.

    2. I still think some kind of discussion and nod of approval from the higher ups had to be given, or else it could be that the higher ups concluded that the authors involved in your article have a record indicating they’d lean toward a position of no evidence shown in the historical record for a connection between hurricanes and global warming.

  71. Roger Pielke Jr.:

    Pat (#70)-

    You’ve mischaracterized our paper. We cite Emanuel (2005) and describe it as suggestive of evidence of a connection of hurricanes and global warming.

  72. Lynn Vincentnathan:

    This may be totally off, since I know squat about climate science & the high-powered statistical programs used, but when there is a dearth of data in the social sciences (not enough to give low enough p values on correlations & regressions, simply due to small numbers of data, which is sometimes due to loading in too many control variables), we sometimes turn to chi-square & log-linear analysis to see if actual data reveal patterns incongruent with expected patterns.

    In this vein, could, say, log-linear analysis be used to see if there were a lack of match between the natural decadal patterns (since we have a good idea about them) and the actual patterns now occurring currently (since we have the actual data on them).

    Forgive me if I’m way off on this.

  73. Roger Pielke Jr.:


    I have just come across your comments above.

    Re: #47 – I can’t read German (I wish I could!), so if you’d be kind enough to email to me a translation of the quote, I’d be happy to respond. I did speak to the reporter for quite a while, so I’d be disappointed to be misquoted, but it happens.

    [Response: Headline (issue 36, p. 124): “Roller-coaster of monster-storms – number and strength of hurricanes is increasing, but this has nothing to do with global warming”. The text says:

    Human caused global warming, however, has nothing to do with the increasing storm-chaos. “A connection between greenhouse effect and hurricanes is so far not proven”, says Pielke.

    (This is my imperfect translation. The first sentence, before the direct quote, uses a tense which I think cannot be easily put into english, which makes it an indirect quote from you, rather than a statement of the journalist.)
    This indirect quote, picked up in the headline, is plain wrong, as you will agree. At most one could say we are not certain whether or not hurricane activity is linked to global warming. The direct quote is technically correct in that nothing is ever definitely “proven” in the Earth sciences. But one should be clear that there is reasonably good evidence for such a connection, both from models and data (see the two figures in our post above). -stefan ]

    Re: #49 – Emanuel’s point and my point are one and the same — Simply put, his PDI metric is not a measure of “destructiveness”. While there may indeed be changes going on in the characteristics of storms themselves, this does not mean that those changes are at all meaningful from a policy perspective. Think of it this way — if there is no chance of observing the effects of changes in PDI in the global impacts record for 50 years (Emanuel’s estimate) and over that same time period we expect damage to increase in real terms by up to a factor of 32 (a real doubling in damages every 10-15 years), then I think that it is safe (and also responsible) to assert that over that time period the only policies that can have a discernable effect on tropical cyclone damage around the world will necessarily be adaptive.

    [Response: Emanuel’s estimate means that globally, the power of hurricanes has increased by ~75% while tropical SST has increased by ~0.5 ºC in the hurricane season, and these two are linked by physical theory, models and by statistical correlation. This remains a real increase and there is no reason to assume that it is not linked to a similar increase in damage, even if this cannot be proven from data because they are too noisy. Bad signal/noise ratio does not mean there is no signal – as Emanuel shows in his example calculation, bad signal/noise is expected here despite a large signal, simply because the data are very noisy. From current understanding, it is reasonable to assume that further warming will contribute to a further increase in hurricane damage, and not by a small amount. In my opinion, this is one of many reasons why it is wise to stop the warming before it goes too far. Putting more people and values into harms way by settling on a highly vulnerable coastline is also likely to increase hurricane damage. I think it is a pointless discussion what is worse – neither adding a lot more greenhouse gases to the atmosphere, nor allowing a lot of development along such a coast without proper hurricane protection measures, seem wise policies to me. -stefan]

  74. Michael Jankowski:

    RE#70 – states, “Typical hurricanes are about 300 miles wide although they can vary considerably…size is not necessarily an indication of hurricane intensity. Hurricane Andrew (1992), the most devastating hurricane of this century, was a relatively small hurricane.”

    Frances was huge, but I can’t find a number. I’ve found links saying “the size of Texas,” which would put it in the 700 mile range. Katrina was about 500 miles wide at some point. By comparison, Andrew was just 60 miles wide.

    I think it’s worth noting that Katrina was a Category 1 when it struck south Florida. If she had veered northward at that point, we wouldn’t be talking so much about hurricanes right now. Katrina would’ve been a relatively minor Florida hurricane and probably mostly forgotten.

  75. Harold Brooks:

    Re: #66

    Thunderstorms in hurricane environments typically don’t have strong updrafts. The temperature profile is close to moist adiabatic and, as such, there’s little convective available potential energy. Also, since the environments are generally warm through the depth of the hurricane, there’s a long distance between the freezing level and the ground. Hail is generally rare with hurricanes and, in fact, so is lightning (in comparison with mid-latitude continental thunderstorms.)

    Re: #70 (2)

    I’m not one of Roger’s NOAA co-authors, but I am a NOAA author of other papers. I’ve never had to get a “nod of approval” from higher-ups for the content of any paper I’ve published, even though some of them have questioned NOAA policies and/or future directions.

  76. Pat Neuman:

    Re 71, Roger, I don’t think I mischaracterized your paper. I’ll take another look. BTW, did your co-authors spend government time doing work on the paper?

    Re 73, thanks for the info. When Katrina struck south Florida, was it nearly as wide as when it hit Louisianna/Mississippi? Did Katrina come ashore with widespread heavy rain like Francis?

    Re 75, Did you use government time to work on your papers? When (date, yrs) did you work on these papers. Did you include disclaimers on the papers? I think the subject of global warming/climate change is a whole different ball game.

  77. Isaac Held:

    I would like to comment on the argument in the initial posting in this thread that one can compare the importance of decadal variability in the Atlantic and greenhouse gas increases for hurricanes by simply comparing the increases in SSTs that they cause. (This is also a continuation of my comment in #40). Suppose for the sake of argument that the Atlantic internal variations are uncorrelated with the Indo-pacific, but that the latter, becuase it provides the deepest, most intense convection on average, controls the tropical tropospheric temperatures above the boundary layer (which we think of as being uniform horizontally). Then, when the internal variability of the Atlantic creates warm SSTs, it also creates a more unstable troposphere. In contrast, greenhouse gases warm both the Atlantic and the Indo pacific, and therefore, they warm both the Atlantic SSTs and the tropical troposphere, hopefully, with no change in stability to lowest order. (By the same argument, ENSO, by warming the troposphere, with only small effects in Atlantic SSTs, would stabilize the Atlantic.) Whether one thinks about buoyancy in this simple way, or one uses the entropy-base arguments for potential intensity of hurricanes, the sense is the same — internal variability should be more important for hurricanes than global warming of comparable SST amplitude.

    [Response: Isaac, I don’t think anyone is claiming that SSTs alone are determinant (since as you correctly point out, tropospheric temperatures and the stability of the atmospheric profile are obviously important). However, to the extent that SSTs are influential it makes sense to assess the possible contribution of a global warming signal to the SST variability. Where your argument might break down is in the assumption that GW would cause uniform warming across the tropics. Given the much greater internal variability in the Pacific and the arguments of Cane et al, that doesn’t necessarily hold true, though it would be worth examining further. -gavin]

    [Response: Dear Isaac, you’ve got a potentially valid point, that hinges on the question which we have not really clarified yet: how important are differences in temperature, and how important is the absolute value of temperature (which does come in due to all the non-linearities, e.g. Clausius-Clapeyron, which are not just small second-order effects). One preliminary test: if your argument is right, the correlation of SST and hurricane intensity should be much higher in the Atlantic, compared to the Pacific or the global (tropical) average. That’s not the case: see Kerry Emanuel’s second-to-last graph here. -stefan]

  78. Eli Rabett:

    To Pat Neuman and Roger Pielke, while I cannot speak for NOAA, most of the national labs I am familiar with have an internal review policy for scientific papers which functions to insure quality (personal axes to grind are another story). Among other things that they look for is that no confidential material is being disclosed and certain other policies are adhered to. Here is one example Here is a general discussion of the issue for national labs. It appears on first glance that NOAA relies on external peer review

    To Michael Jankowski, it appears that you never saw a headline that says man falls asleep, plows into tree at 70, dies. Please, you have constructed a stawman. There are enough people who die in high speed crashes when they fall asleep. At slower speeds they are only mangled.

  79. Harold Brooks:

    Re 76:

    Yes, it was on government time. I worked on the papers from 1992 to the present and continue to do so. No disclaimers were put on them. I have seen no difference in any climate-related papers. A quick glance at NCDC climate change papers shows no disclaimers either on the first several I looked at on the AMS archive and they were all supportive of significant climate change in recent years.

  80. Pat Neuman:

    Re 78

    After reviewing your linked refererences, I think many of the agencies or offices which are under the NOAA umbrella have their own internal review policy for scientific papers. This will likely be my final post here on this subject.

  81. Michael Jankowski:


    You continue to twist my analogy immensely, ignore my points, and argue against points I have never made.

    I am sure we agree that, assuming all other things are equal, a hurricane with higher wind speeds is more destructive than a hurricane with lesser wind speeds.

    But I am not sure that you agree, however, that all other things are not necessarily going to be equal. It seems reasonable to me that if AGW can significantly affect wind speeds in hurricanes and weather patterns throughout the world, then other factors determining the paths and destructiveness of hurricanes can also be affected by AGW. Some may be generally bad, some may be generally good, and some may be either good or bad on a case-by-case basis. Does this not seem reasonable to you?

  82. Roger Pielke, Jr.:

    Re: #73

    Stefan- Thanks for these comments, we may simply agree to disagree on these points. Some additional thoughts.

    1. You write, “This remains a real increase and there is no reason to assume that it is not linked to a similar increase in damage, even if this cannot be proven from data because they are too noisy.” If you can’t see a signal in a noisy record then by definition that signal is not large with respect to other relevant factors. If I can’t see a climate signal in the damage record, I agree with you that this does not mean that a signal does not exist, but it does lead one to conclude that the signal has not thus far been important from an impacts/policy perspective. Policy deals with (or at least should deal with) causing detectable effects, not addressing effects that cannot be detected. And again, Emanuel himselves estimates 50 years before any signal can even be detected.

    [Response: “…then by definition that signal is not large with respect to other relevant factors”. Nope, not quite logical. That signal then is not large compared to the purely random, stochastic elements. Kerry’s example shows we could not remotely prove even a 75% increase from landfall data. If global warming has caused a 75% increase in hurricane damage, then this is definitely policy-relevant, no matter whether your damage statistics can attribute it or are just too noisy for that. I suspect you are thinking: if my statistics don’t show the effect, then it can’t be a serious real effect. But that’s not true. Remember the loaded dice: assume your friend rolls it 10 times and gets 4 sixes. Assume without the dice being loaded, he would have gotten 2 sixes. So loading the dice had a huge impact. Yet, by analysing the statistics of those 10 rolls, there’s no way you could have demonstrated that the dice is loaded. You couldn’t tell whether the 4 sixes occurred just by pure chance. But if for each six you were losing $ 1000 to your friend, this would be highly policy-relevant for you: you would stop playing with him if you had good reason to think his dice were loaded. You would stop playing if you had some other, indirect evidence that the dice are loaded (say, like Kerry Emanuel telling you after having x-rayed the dice). You then wouldn’t play on until your loss statistics unequivocally prove that the dice were loaded, unless you’re stupid. Do the maths: how many rounds would you have to keep playing with doubled odds for losing until you can prove at the 95% confidence level that you’re being cheated? Would you really keep playing all those rounds, brushing aside Kerry’s x-ray pictures with the argument: I don’t see statistically significant losses yet, my losses are large but still within the even larger bounds of random chance? I wouldn’t. – stefan]

    2. You write, “I think it is a pointless discussion what is worse [climate change or societal vulnerability].” I’m surprised at this statement. Policy has to be based on an assessment of alternative courses of action, and justifications for action that lend themselves to political accountability. If one has a goal of addressing the future impacts of extreme events on human society, then the most important question from a policy perspective must be “What options do we have to act, and what are our expectations for the consequences of those alteratives?” Understanding the reasons underlying undersirable outcomes must be part of our research portfolio, lest we act on assumption, hunch and political predispositions, none of which, in my view are as effective a basis for action than science. I agree with you 100% that we should address both greenhouse gases and societal vulnerability, but we should not pretend (and yes, until it is backed by science it is pretending) that these issues are one and the same. They are not. There are good justifications for reducing greenhouse gas emissions, but having an discernable influence on future hurricane dmaages is not among them.

    [Response: Of course they are not the same. But you have to be clear that the two effects multiply – they do not just add up. Above (#73) you juxtapose a 32-fold increase in vulnerability due to population etc., to a non-discernible climate effect – say a 2-fold increase in hurricane power (roughly as seen in Fig. 2 of the post above), suggesting the latter thus must be unimportant. That’s not the case. If your 32-times larger values are struck by a twice-as-damaging hurricane, the resulting damage would be 64-times larger. In numbers: assume that decades ago, the damage from hurricanes would have been ~3 billion $. Now, after 32-fold increase in values, the same hurricanes would have caused ~100 billion $. But if hurricane power had doubled, that would rise to ~200 billion $. So even though doubling sounds like a lot less than a 32-fold increase, this is highly deceptive. It still remains that in this theoretical example, half the $-damage is due to climatic effects, not population! And that remains true even if the data are too noisy to prove the twofold increase statistically – you still have to pay this bill, see the example with the dice above. Perhaps I’m biased because I’m a physicist not a statistician, but to me it is clear that physical evidence, like our physical understanding of how CO2 affects SST and how SST affects hurricanes, gives you warning of the loaded dice long before you can prove it from the damage statistics. Kerry, hand me those x-ray pictures – I’m not gonna keep playing this game, ignoring the physical evidence, waiting until the losses are so huge that even very noisy statistics become unequivocal! -stefan]

  83. Lynn Vincentnathan:

    RE #75, thanks for your response. It was mid-July; we’re a subtropical area (lat 25.9N), and we were in the throws of El Cunecula (regular, but intensified summer heat wave) when Emily with hailstones came. So, I guess our weatherman was right, hailstone are unusual in our hurricanes.

    RE #79, great, so glad at least some of my taxes are going in the right direction. I think all branches of government should be addressing GW in their own ways – afterall, it IS “global,” which includes the U.S. I keep writing my reps “What are you doing about this,” and they keep responding “The science isn’t in yet,” and I keep responding, “Yes, it is — more than enough for policy decisions.” Of course, they get their science from the WSJ. So, it is indeed good that a few in gov are actually into the science of GW. Just too bad those that make life & death decisions for us are not.

    And before the contrarians who claim science should be kept clean of policy & politics jump on this, I agree with you – I want science to strive after objectivity, let the GW loaded dice fall where they may. This post is not violating that principle, rather it is critiquing the situation of policy & politics keeping clean of science, which they should NOT do, because that amounts to the blind leading the blind into very troubled waters.

    As a social scientist, I am interested in this perspective. Our Enlightenment mindset of analysis (cutting up, compartmentalization, div of labor, pulling apart the clock to see how it works) – great for most science, not so great for all of life. I think in science & life we now need some synthesis, bringing together, putting the clock back together, connecting science to policy, bringing in more variables into science, an integration of the physcial sciences with the social/behavior sciences (perhaps with the humanities), the university with laypersons. United we stand, divided we may fall.

    Part of this problematic Enlightenment mindset is the either/or focus. I liked Stefan’s response to #73 – Why can’t we do both, (1) better prepare for the effects of GW AND (2) try to reduce GW. The money we save from 2 could be plowed back into doing 1.

  84. wayne davidson:

    #73: “There are good justifications for reducing greenhouse gas emissions, but having an discernable influence on future hurricane dmaages is not among them. ”

    Is a statement which defies logic, the very source of energy creating powerful hurricanes is greater moisture generated by more heat. I rather like an explanation, are hurricanes not heat dependent? Never mind destruction statistics, which vary according to hurricane paths. The implication of this statement reads like GW has no disercnable influence on hurricanes, like GW has nothing to do with warmer air.

  85. Roger Pielke, Jr.:

    Re: #84

    It is possible that GW has a discernable influence on hurricanes and yet has no discernable influence on hurricane impacts (however measured). For an undersatnding of how this can be the case see this paper:

    Pielke, Jr., R. A. and D. Sarewitz, 2005. Bringing Society back into the Climate Debate, Population and Environment, Volume 26, Number 3, pp. 255-268.

    And I agree with Lynn (#83), we can and should be doing both sorts of things, but to do so effectively means not conflating them as one and the same.

  86. Joseph O'Sullivan:

    I think Roger Peilke Jr is asking a hybrid climate science / regulation question. On the scientific side climate modeling and physics show a potential increase in TC intensity that correlates to global warming, and now there is evidence that this is actually happening. This increase in TC intensity has not had a measurable socio-economic impact and possible further intensity increases might not have a large socio-economic impact. The question then is what kind of regulatory action should be based on this information. I think it’s a reasonable policy question.

    There is some good info about TCs and climate change
    Pew has a release
    MIT’s Robert Korty, a scientist specializing in climate and hurricanes wrote a short article

  87. Lynn Vincentnathan:

    RE #84-86, as mentioned before while natural causes may go into creating the largest part of hurricane intensity, we have to figure GW’s part as an add-on at the upper level – and it is that last bit of intensity that might do the most damage, more than the first incrememts (assuming the hurricane make landfall in a populated/built area). So while GW’s part may be small, its effects could be very large. I think that should be more our focus from a policy standpoint than, “GW’s part in hurricanes is small, and its effects may be negligible.”

    As Roger points out, there are many other (even better) reasons for reducing GW. However, I think we can add “reducing hurricane intensity” to our list, even if it doesn’t have as much results as in reducing other GW effects (I’m thinking of droughts in Africa & glacier melt in the Himalayas, which could put 40% of Chinese & South Asians at severe water shortage risk – no water to drink, much less to irrigat crops).

    I can see the problem: If we focus solely on hurricanes, and not the entire list of effects, we might lose some of the “intensity” in our pleas to get people to reduce GHGs. And some people even get confused and bored with the long list of GW harms, which just keeps getting longer.

  88. Eli Rabett:

    Dear Michael, NO. Why? Because the first order cause of hurricanes is temperature differences between the surface and the upper atmosphere. My experience over 30 years of work in the natural sciences and the unnatural (engineering) is that balancing becomes important ONLY for secondary issues. The reason is that if you have an major cause, it takes a whole lot of secondary effects all going in one direction to restore the balance. Mostly the secondary effects go in both directions and balance themselves out. A good example is how the climate sensitivity to 2x greenhouse gas forcing has remained pretty much the same, with pretty much the same variation between estimates for a whole lot of years, model sophistication and generations of Moore’s law.

    In a lot of ways your argument is like the student who shows up before the final with a passel of F’s on tests and asks if they can get an A in the course. The stars would have to align, the second coming be announced and then maybe.

    A good reason why it is dangerous to take up your argument, is that it is equally likely that the secondary causes go against you. Plan for the worst. Pray for the best. Don’t trust economists. They have no clue about assigning costs.

  89. Steve Latham:

    Re 81 & 88. I think you two actually agree. One thing I was told in no uncertain terms in an undergrad conservation biology course was that analogies are very dangerous when you want to explain science in a politically-charged realm. The analogy breaks down and people tend to focus on parts that really aren’t most relevant to the point being made. For example, who says that driving a long time was the main contributor to falling asleep (maybe it’s the engine sound at 70 or some other thing)?

    But I enjoy analogies and I think Michael’s was very persuasive in suggesting that going back and looking at what damage hurricanes like Katrina would have done without AGW or with more is an exercise that could be done for interests’ sake only — knowing with any certainty would require a lot more information (I’d say an impossible amount) about how AGW affected other aspects of the storm. On average higher windspeed = bad, but what was proposed was not to look at things on average but to look at a specific case. I don’t know if things could have been much worse than they were with Katrina, but if they could not, then it’s quite possible that more AGW would have lessened the damage done (if not the inherent destructive force). Disagreeing with the forensic approach does not necessitate an attitude against assigning blame in general or against policy prescriptions to deal with future likely impacts, so I don’t think Michael was advocating that people plan for the best.

    I’ll stop putting words at your mouths now.

  90. wayne davidson:

    Re 85

    Thanks for the paper

    Since hurricane paths don’t always hit the same city, having an identical population, likewise buildings and economic infrastructure, it is incorrect to make hurricane financial impact assessments while looking at a long time spans, an analysis without nearly identical landfall scenarios doesn’t mean much. However, if you shorten the time span, compare it with nearly identical demographics at landfall, you may find a better trend aside from the ‘grass” talked about above. Forecasting future hurricane impacts is done with clarity provided in Hurricane historical met records as proposed at the top of this page. Intensity is a key issue, which will continue to increase along with GW, however Cat 3-4-5 hurricanes/typhoons are not confined to landfalls, but intensity with a few other met parameters readily show the impact of GW (as showed above) . It is perhaps a matter of time before someone demonstrates a clear and proper hurricane destruction cost comparison, I wonder if it is possible given very significant temporal urban demographic disparities.

  91. Roger Pielke Jr.:

    Re: #82

    Stefan- As much as I like to engage in abstract philosphical arguments about dice they are unnecessary when we have a good quantitative, scientifically rigorous, empirically-based literature on climate impacts. Some points to ponder and literature to consider:

    1. The same hurricane damage database that is too small a sample to show a correlation with the Atlantic basin, annual total PDI is perfectly able to show a very strong statistical relationship with another climate index, the annual ASO Nino 3.4 temperature anomaly index. See this paper:

    Katz, R.W., 2002: “Stochastic modeling of hurricane damage.” Journal of Applied Meteorology, 41, 754-762.

    So why is it that we can see the effects of ENSO in the damage record but not, for example, the annual Atlantic basin total PDI, given the exact same randomness in impacts? Perhaps one index has a stronger relationship with damage than another, no?

    2. Similarly, we have been able to show a statistical relationship between various measures of precipitation and flood damage, even though the spatial and temporal area that experience floods are far smaller than the regions over which precipitation is measured. We do get the strongest relationships at the basin level, of course where precipitation is integrated, but we also see a correlation at larger scales. See this paper:

    Pielke, Jr., R.A., and M.W. Downton, 2000: Precipitation and Damaging Floods: Trends in the United States, 1932-97. Journal of Climate, 13(20), 3625-3637.

    Again, some metrics have a stronger relationship with damage than others. There are good physically based reasons for this.

    3. Let’s completely set aside the issue of trends, Emanuel’s PDI (for the Atlantic basin, annual total) is not correlated with historical damage. The ASO Nino 3.4 index is strongly correlated with historical damage. This tells me that the ENSO index is a very good predictor of damage and the PDI simply is not (FYI, nor is the ACE index used by Gray et al.). There are however climate indicies that are related to damage, such as the decadal AMO, see this paper:

    Landsea, C. L., R. A. Pielke, Jr., A. Mestas-Nuñez, and J. Knaff, 1999: Atlantic Basin Hurricanes: Indicies of Climate Changes. Climate Change, 42, 89-129.

    So long as some climate indicies prove to be better than other indicies for explaining historical damage, it seems unsatifactory to claim than “randomness” can explain why one particular index has no correlation with damage. A different explanation to consider is that there is in fact not a strong relationship between PDI and damage and projections of future changes in the PDI provide little basis for asserting any effects on damages. But these are questions that can resolved through rigorous research (e.g, IPCC WGII-type research). They won’t be resolved through philosphical arguments! ;-)

  92. Heiko Gerhauser:

    Re 82

    To stick to Stefan’s example. I think Roger would argue that there are other factors we have more control over, which would be decisive and statistically detectable, such as whether to play the game in the first place (not so much settlement in vulnerable areas), or whether to incur damages of $10 or $1000 (build better dikes).

    You earlier gave the example of the European heat wave. Now, climate change so far, has loaded the dice there, as you suggest. Said loading is roughly equivalent to living 100 km further South, which has no discernable socio-economic impact. That’s not just because of noise hiding an underlying trend. It’s because adaptation to the higher temperature is such an important variable here that it can make the effect of the higher temperature on mortality / life expectancy go away entirely.

    I don’t doubt that the heat wave caused excess death, particularly among already frail people, and when compared to a more moderate previous August,

    but I also think that the small temperature increase so far over Europe’s had no net effect on mortality or life expectancy, not just because of the noise being more important than the small change, but because the noise interacts with the small change (a little bit more air conditioning here, a little bit less heating there, people moving for retirement to Spain etc.).

    [Response: Heiko, I’d agree with your argument if climate change were smooth and gradual. Then, the 1 ºC warming we’ve had in Germany over the past century would have hardly any human health impact, and could indeed be compared to climate zones shifting by x km. It would be easy to adapt to. The reason why things turned out otherwise, and we got 30,000 casualties, is non-linearity and surprise. June temperatures in 2003 were 7 ºC above the long-term average – 5 standard deviations! And this came by surprise. Studies have shown that it is highly likely that global warming made a big contribution to this extreme event, but clearly it cannot be explained just by a smooth warming trend of 1 ºC per century. The more we interfere with the climate system, the more likely it is that it will respond in surprising and unforeseen ways, that we are poorly prepared for. It is not a linear system. Wally Broecker once said: the climate system is like an angry beast, and we are poking it with sticks.
    By the way: our own infrastructure also induces big non-linearities. Suppose you have a system of dykes that protects against hurricanes of category three. Perhaps global warming might add 10% of energy to a hurricane, and it’s just that extra 10% that make the dykes break. That would hugely increase the damage – would you attribute that to the warming, or just to tough luck? -stefan]

  93. Michael Jankowski:

    Re#88 Eli,
    Interesting – you say “NO,” that it is not reasonable to assume AGW could significantly affect hurricanes in other ways, then you start talking about “secondary issues.” If you are open to the possibility of secondary issues, whether or not they are good, bad, or “cancel out,” then your answer should have been “yes.”

    I do like the “stars would have to align” portion of your analogy. Metaphorically speaking, that’s along the lines of what it takes for a hurricane to hit a particular spot. 0.5 deg more of warming (or cooling) doesn’t affect that?

    Re#89 Steve,

  94. Jonathan Jett-Parmer:

    I am intrigued by your site and have a couple of questions.

    1) If, as you state, the EU has the following goal;

    “This is a completely moot point. Kyoto or any other measures are not designed to make a difference within 5 years, which is obviously impossible given the timescales of the system. There is a world of difference, however, between having 2 ºC warming by 2100 (which is the policy goal of the European Union) or having 4 ºC or 5 ºC or even more warming then, and this is what we can decide.

    What model is used to effect a 2 or 3ºC reduction in planned warming? And what model predicts a 4 ºC or 5 ºC rise by 2100? Given 95 years at fractional reductions, I would like to understand the algorithm.

    2) In the Emanuel 2005 study, what was the nature of the PDI equation? Were hurricanes measured on size and intensity? Does the lack of comprehensive data from earlieir periods account for the VERY significant spike in PDI?

    3) Finally, for the climate novice (that would be me) can you recommend some well vetted texts or articles to get a good grip on the current state of thought?

    [Response: Check the science links sidebat: AIP for history; IPCC report for the current state – William]

    Thanks, I appreciate a well written scientific site!

  95. Heiko Gerhauser:

    Re 92

    My reading of the consensus is that it is very likely that climate change will be “smooth and gradual” over this century.

    Not to dwell too much on semantics (on what smooth and gradual exactly means in the context of a hardly constant weather), as far as temperatures over Europe are concerned, my understanding is that night time winter temperatures will rise most, and summer maximum temperatures least and that otherwise the variability of temperature won’t be affected much.

    You seem to be saying that the heat wave wasn’t just made half a degree C warmer by climate change (as per previous sentence a bit less than the global average), but several degrees warmer.

    This is completely contrary to what I thought the consensus on climate science said.

    I know that sudden, unpredictable climate change is an issue with a potential policy impact.

    I think it’s small for the following reasons:

    1. My understanding of climate science is that all truely serious scenarios of sudden climate change are quite unlikely.

    There are known low likelihood dangers, such as a major meteorite strike, and the likelihood for these does feature in determining the scale of our mitigation efforts, even though the potential consequences could include the Earth becoming uninhabitable.

    2. We’ve changed lots of other things, a little extra warming may not only cause sudden climate change (The Gulf Stream is a frequently cited example), but help to prevent it or attenuate its effects.

    3. While climate may be a beast, in many respects it’s an exceedingly slow one with lots of inertia. As you’ll be well aware, surface air temperatures can easily change by 10 C within a day, for large bodies of ice to melt, or sea water to warm would take centuries. The kind of instantaneous climate change depicted in a certain rather well known movie is, as you also will be well aware of, physically impossible.

    In other words, there are some (policy relevant in my opinion) limitations on how bad climate change can get, even when considering exceedingly low likelihood worst case scenarios.

    If India gets the climate of Saudi Arabia, say, while climate models aren’t predicting that, it appears to be a pretty horrendous outcome.

    However, it’s actually one that can be adapted too, eg through large water projects, the importation of grain and air conditioning.

    Of course, if India becoming a desert was a certain outcome of climate change, or even a likely outcome, I would deem this to be of major policy relevance. It’s the combination of low likelihood and limitations in the impact that I think makes it a weak argument for influecing policy.

    After all, if there was an even 1% chance of a meteorite wiping out humanity over the next century, we’d probably gladly spend 5% of GDP to prevent it. We aren’t willing to spend 5% of GDP on a 1 in a million chance of that, and even less willing to spend that kind of money on an unlikely event that is adaptable to without major loss of life, just major economic (and social disruption and ecosystem) cost, should it strike.

    Climate change, unlike many other risks (such as new diseases, very large meteorites, nanobots etc..), does not have the potential to wipe out humanity, and “India turning into a desert” type worst case scenarios are, at least that’s my understanding of the current state of climate science, exceedingly unlikely.

    Finally, regarding the dike example, well global warming would raise the likelihood of it getting breached. We could try to reduce that likelihood by making the dike cat 5 proof (at a cost), or by changing energy policy.
    We could also use engineering works (it’s not only natural wet lands that can do this job) to break/divert part or all of the storm surge, so that even a cat 5 would only yield a storm surge at the dike that previously a cat 3 would have done, thereby reducing the non-linearity introduced by what happens when the dike does get breached.

  96. Tom Huntington:

    Regarding the question of trends in hurricane intensity, there is another analysis that I think is worth mentioning.

    In a recent paper Saunders and Lea (2005) reported that July wind anomalies (averaged between heights of 925 and 400 mbar) are well correlated with the US Accumulated Cyclone Energy (ACE) an index of intensity of land-falling hurricanes in the US for August through October. They stated that “the wind anomalies in these regions are indicative of atmospheric circulation patterns that either favour or hinder evolving hurricanes from reaching US shores.”

    Additionally, and as yet unpublished, Mark Saunders (University College London, Benfield Hazard Research Center) presented a paper (Tropical Cyclones in a Warmer World) in October 2004 at a Workshop entitled “Natural Hazards in a Warmer World” Workshop for Under 35s Reinsurance Group.

    In that workshop, reporting on trend analysis in ACE in the Atlantic and Pacific Oceans, Saunders concluded that “No significant change in ACE index or ACE index variance is observed anywhere, either over the full period or, for the U.S., using the recent 1978-2003 period compared to prior 26-year periods. The change in ACE index due to natural climate variability is everywhere an order of magnitude greater than that which may be attributable to trend in the historical record. Global warming has, at present, had little or no increasing impact on northern hemisphere tropical cyclone activity.”

    Saunders, M.A., Lea, A.S., 2005. Seasonal prediction of hurricane activity reaching the coast of the United States. Nature 434, 1005-1008.

  97. Roger Pielke Jr.:

    re: 2nd reponse to #82 above


    I much appreciate the continuing dialogue.

    Lets ground this discussion in science and not abstraction. The IPCC SAR suggested a 10% increase in MPI of TCs by 2050. Knutson and Tuleya (2004) suggest a smaller increase, 5% by 2080. There are no studies that I am aware of that provide a clear picture on frequency (see Pielke et al. 2005 for a review). Emanuel (2005) offers no projections.

    I am aware of no reason in the scientific literature to believe that the destructive power of hurricanes will double, as you suggest, over the next 50 years. Were that to be the case it would be unavoidably evident in the damage record. That is an extremely large signal (e.g., of similar magnitude to what we can easily observe in the damage record between warm and cold phases of ENSO). If science supports such claims I will readily accept them. Right now the conclusions of the IPCC lead one to conclude that the effects of societal changes will exceed climate changes by a ratio of 22 to 1 to 60 to 1. If we were instead to use the more recent work of Knutson and Tuleya, then these ratios would be something more like 44 to 1 to 120 to 1. What this sensitivity analysis tells you is where, from the standpoint of action, you have the greatest ability to affect future impacts. See Figure 6 in this paper:

    So which conclusions of the IPCC do you reject? The effects of climate change on hurricanes? Trajectories of population and development? It seems to me that, logically, if one accepts the views presented in the IPCC, then one also has to accept the analysis I have presented here.

    Don’t get me wrong, we should be taking more effective actions to decarbonize the global energy system. But repeated claims that such actions will materially affect disaster losses in coming decades are simply inconsistent with current scientific understandings. I enjoy discussions about loaded dice as much as the next person, but when we have rigorous research available on climate impacts, it seems to me that we should focus our discussions there.

    [Response: Roger, I feel condescension and insinuations about my arguments not being grounded in science are inappropriate. I was using the dice analogy as an everyday and non-political example, since such analogies can often help to understand some of the basic concepts. But my argument is essentially based on Kerry Emanuel’s data (which of course post-date the last IPCC report), and I was talking about the trends observed by him for the past, not about future projections. Kerry’s study has found that the power dissipation index has increased globally by 75% and in the Atlantic it has doubled over the past decades, that’s why I was using those numbers. If those numbers are correct, and the PDI is closely related to potential destructiveness (see our footnote to the post above), then there is no way your ratios above could be correct. Any increase in societal vulnerability, no matter how large, would be multiplied by 2 due to the increase in storm power, so the latter would always be the larger contribution to the damage. We can debate how robust Kerry’s data are, they are quite new and surely there will be further analysis of the observed trends – but I think we can say at this stage that Kerry’s data directly contradict your conclusion about the small contribution of climatic trends to the damage. -stefan]

  98. wayne davidson:

    Not that I am a big fan of economic impacts, I would suggest looking at Camille vs Katrina, or likewise hurricane landfalls as far as truer comparisons, and of indirect evidence proving Global Warming. Much more interesting would be discussion of hurricane diameters for instance Andrew vs Katrina and the climate creating both of them. Those claiming that predictions of greater damage to come are exagerated, should look no further than Katrina’s impact, heard is about $200 billion US now, certainly the biggest one in history despite other monster hurricanes in the past.

  99. Eli Rabett:

    Re # 88 Michael, perhaps I was not clear enough. If you have a primary cause that is responsible for 50% of an effect, and three causes that are each responsible for 13%, each, all three secondary causes would have to break in the same direction to compensate for a change of the same magnitude in the primary cause. Admittedly this is a simplification, but it is a useful thing to keep in mind for most yes but arguments. A lot of people miss this point, but it is also why simple models that isolate primary causes work pretty well.

  100. Eli Rabett:

    The problem with making economic arguments about disaster impacts is that a very small number of disasters account for most of the costs. Katrina going 30 miles in one direction can change the cost of storm damage in 2005 by an order of magnitude without changing the intensity of the storm at all. On the other hand, if nature increases the intensity of large hurricanes in the South Atlantic and Carribean by a factor of 50%, sooner or later one of them is going to cause massive damage. Worse, there is some probability that a Katrina or a Katrina^1.5 would precipitate recession or worse. How would you account for that cost? Sort of like playing with Dirty Harry, just how lucky do you feel?

  101. Michael Jankowski:

    Re#98, Katrina is a tough example to use. Essentially the same $$$ amay have occurred had a much weaker storm hit. If the levees had held (and information I’ve seen said the levees were damaged by barges and that they were supposed to hold-up even to a Category 5 without breaching), the damage/cost would be immensely lower. Maybe I’m short-changing the damage Katrina did elsewhere (I’m under the impression the New Orleans devastation is going to be the bulk of the hurricane damage and that, in turn, the bulk of the New Orleans devastation was due to the post-storm levee failure and not the storm itself).

    Re#99, The future is supposed to be a warmer and subsequently wetter world due to AGW, so I’d say “wetter” is what you would call primary. Yet models seem to suggest many areas of the earth will become much drier, thanks to changing weather patterns (althought they often disagree on which areas will warm the most, which ones will get the wettest, etc). So obviously being “secondary” can have some substantial effects according to our climate models.

    Maybe you don’t like that climate-related analogy, so let’s talk about hurricanes specifically. As stated here : “During the 112-year period for which the NC State researchers have data, an average of 3.23 tropical cyclones pounded the East Coast each year. During El Nino years, that number dropped to an average of 2.47 storms. North Carolina saw an overall average of 0.81 tropical cyclones annually, and 0.56 during El Nino years.” We also know that we tend to have fewer hurricanes in general in the Gulf and Atlantic during El Ninos in general, not just East Coast landfalls. There are those who theorize global warming will lead to more frequent El Ninos (and the evidence suggests El Ninos became more frequent in recent decades) – and, hence, fewer Gulf and Atlantic hurricanes to worry about assuming everything else stays the same. Some even suggest El Nino will start lasting for periods like 18 yrs instead of 18 months! And as reported elsewhere and on this thread, there doesn’t seem to be any evidence of increased hurricane frequency overall due to 20th century warming. If AGW doesn’t intrinsically increase hurricane frequency (just strength) but does increase El Nino events, then we should see a decrease in Gulf and Atlantic hurricanes and landfalls. Going by the East Coast data above and assuming El Nino conditions account for roughly 1 yr out of every 4 in that 112 yr study period, you end up with about 40% less hurricanes under El Nino conditions. So if El Nino conditions become more frequent, I’d say the evidence suggests significant reductions in hurricane frequency and landfall. Will such a reduction negate the impact of stronger hurricanes, or possibly even overwhelm it? I don’t know, but I don’t see any evidence to suggest pooh-poohing it as “secondary” and assuming it’s inconsequential, either, as you seem to suggest doing.

    Re#100, I’d like to see the cost comparison between the results of Katrina^1.5, Katrina, and, say, Katrina^0.5. While the destruction outside of New Orleans may have been much different under each, I’m not sure the destruction of New Orleans itself wouldn’t have been basically the same (almost certainly wouldn’t have been much higher in New Orleans under Katrina^1.5, disputable in Katrina ^0.5 because of the levee-break situations), and I am under the impression (whether correctly or incorrectly) that the devastation of New Orleans is going to be the bulk of the “cost” of Katrina. So I’m not sure those costs are significantly different from each other (assuming the levees fail in each scenario).

    I found this statement of yours particularly interesting: “Katrina going 30 miles in one direction can change the cost of storm damage in 2005 by an order of magnitude without changing the intensity of the storm at all.” This was EXACTLY the major point I was making earlier about trying to assing a x% cost of Katrina’s damage to AGW and what the 55vs65vs70mph driving analogy was trying to demonstrate! Small changes in hurricane paths, as you indicated, drastically affect of the amount of devastation, and intensity is not the only major issue. So unless you feel AGW couldn’t/wouldn’t influence the path of a hurricane from formation to landfall by more than a few net miles along the coastline (which I have a very hard time believing…the width of paths of hurricane forecasts 48 hrs in advance often range in the scale of hundreds of miles alone), then you’ve been in agreement with my car-driving analogy all along! So what exactly have you been attacking it for?

  102. Mark Bahner:

    Roger Pielke Jr. writes, “Don’t get me wrong, we should be taking more effective actions to decarbonize the global energy system.”

    According to Jesse Ausubel at Rockefeller University, we’re ALREADY decarbonizing the global energy system at a rate that will essentially *eliminate* carbon dioxide emissions by the end of this century:

    What’s more, methane atmospheric concentrations (judged the second-most-influential greenhouse gas) have ALREADY plateaued:

    On your Prometheus weblog, Dr. Pielke, you asked for opinions on what the effect would be of cutting CO2 emissions to *zero, today* (ignoring that this is impossible). I responded that the earth would warm by about 0.5 degrees Celsius in the 21st century if worldwide emissions of CO2 were cut to zero today.

    I also noted that the warming that could be expected from “business as usual” would be about 1.2 degrees Celsius. (Such a warming is completely compatible with CO2 emissions estimates that would result from Jesse Ausubel’s projected CO2 decarbonization trend.)

    So I have some questions for you:

    1) Do you accept those estimates (0.5 degrees Celsius warming for cutting CO2 immediately to zero, and 1.2 degrees Celsius for “business as usual”)?

    2) If you do not accept those estimates, which do you think is too high or too low?

    3) If you DO accept those estimates, why do you think “we should be taking more effective actions to decarbonize the global energy system”?

  103. Pat Neuman:

    Hurricanes, floods, other severe weather events and droughts often have regional or local economic impacts. Katrina’s impact is national and world. More hurricanes with national and world impacts are likely as global warming continues. Widespread heat waves, worse than Aug 2003 in Europe, will become numerous and more severe in the years and decades ahead, having critical national and world economic impacts. More importantly, what will the impacts be to Earth’s vegetation, needed for survival of all animals on the planet?

  104. vaughan thomas:

    Re: 97

    Perhaps this is too basic, but I can’t see why discussing loaded dice isn’t “science” in terms of climate. Climate itself is an abstract, statistical concept, is it not? Climate as I understand it is the average of the weather conditions–it is inherently statistical. Otherwise, aren’t we just talking about the weather?

    [Response: Climate is more correctly the statistics of weather, rather than just the average. It is certainly a statistical concept, but I wouldn’t see it as an abstract one – William]

  105. Lynn Vincentnathan:

    RE #100, I just read an article about “How GW Will Burn Your 401K” in PLENTY (Oct/Nov 2005). So in addition to that recession, they write: “When a company has to pay for its direct ecological impact, compliance with environmental regulations, and higher energy costs–or even, in some cases, its reputation as a polluter and lawsuits that arise from its un-green practices–its stock price can plummet.”

    Re Katrina, I have been slow to blame people, because I don’t think anyone really understood just how intricate & interconnected everything is. Take us computer people, we might go bezerk with simply a computer failure. All systems failing and being wiped out in an area, even if people are left alive, is something we can’t calculate very well before hand. Now, in hindsight, there will be calcuations & an awareness of reverberating impacts.

  106. wayne davidson:

    #101 comment about #99

    I am humbly inferior to model calculations per second, but current models lack resolution in a spatial sense, therefore our brains can outmatch them with concepts. The greatest inspiration for heat and moisture AGW effects can be seen daily on satellite animations with particular attention to the equator and the polar regions, the equator ocean air surface plays a daily explosion of convective clouds, almost like a pulse, while in the polar regions most clouds are flat and grey covering a wider geographical area. Convective activity needs stable air above, while in the Arctic the air is more chaotic with all kinds of winds and moisture aloft, truly lacking also heat and therefore convective clouds. For a perspective of a world warming , differential heat from zone to zones , the heat engine of the atmosphere, will change an adjust itself in a new balance regulated by the flow between warm and cold zones. Conceptually wise, it may be a mistake to say that when GW takes effect the air will be drier, but rather water vapour density increases with temperature and relative humidity will drop accordingly, it is perhaps this is what the models are calculating. It is another fallacy to say that there will be more clouds driven by AGW because of more evaporation, for the same reason R. Humidity should drop creating less clouds, reducing cloud albedo making the earth even more warmer. Hurricanes merely reflect the state of energy transferring from ocean to air, by way of water vapour, and are very good indicators of the state of energy of atmospheres in some near tropical locations. The greater the water vapour density of air, the more potential energy it has.

    [Response: The situation is too complex to allow simple reasoning to tell you which way the clouds will go. As it happens, just about all models predict that RH will stay about the same – William]

  107. Chuck Kutscher:

    I am curious as to what sort of increase in Dr. Emanuelâ??s power dissipation one might see during an earlier peaking period in the Atlantic Multi-decadal Oscillation (e.g., from 1920 to 1940). Are there sufficient data to calculate this? This could tell us if the recent large rate of increase in power dissipation is unprecedented and thus likely linked to global warming.

    [Response: Kerry Emanuel’s starting date (1950) is in the middle of the previous maximum of the AMO (see Sutton and Hodson, Science, 1 July 2005). Also, his SST data (see our Fig. 2 above) go back to 1930, thus covering the whole previous warm phase of the AMO. Assuming the high correlation of PDI and SST holds up, this suggests that current values are indeed unprecedented. -stefan]

    Regarding the question of why Dr. Emanuelâ??s increase in power dissipation over the last 30 years is greater than climate models would suggest, could this be due to the increases in subsurface sea temperatures reported by researchers at Scripps and Goddard? As Dr. Emanuel suggests in his paper, large hurricanes significantly churn up the ocean and bring subsurface, cooler water to the surface (and vice-versa). This cooler water should serve as a negative feedback mechanism and limit the hurricaneâ??s power. But if the subsurface water is now also warmer as a result of global warming-induced surface heat being transported downward by diffusion and mixing, this will allow a hurricane to continue to build in intensity. (It seems conceivable that the cooler subsurface water down to the hurricane mixing level has taken many years to capture the surface heating, but now that it has, we could experience rapidly increasing hurricane intensities.) Do any of the models account for the latest subsurface temperature profiles by Barnett et al. of Scripps and hurricane-induced mixing?

  108. Matthias Brun:

    Just three weeks ago there was a century flooding along the alpine countries of Europe – sadly, it was the second so-called ‘century flooding’ in only 6 years. This means that it might be only a 6-year flooding instead of a 100 year one. Only one week later New Orleans is flooded by hurricane “Katrina” and apparently it just lost some power before impact. Knowing that the frequencies and intesities of flooding and the hurricanes are increasing do we really want to know what a real big incidence looks like under the New circumstances of climatic change? If so, then good night! I believe that it is time to
    wake up for everyone and think about what is really important to us. How about parting with growth and competitive thinking. How about saying good-bye to ego-materialism and beginning to shift in the direction of values likecollaboration and group spirit. How about we distribute work and wealth, getting more time for personal development and society, use less fuel, leave your car at home or get a smaller one and turn off television. Mother nature will reward us. The Knowledge has been there for quite some time, it is now time for mankind to take its responsibility.
    Matthias Brun, world citizen from Thun, Switzerland

  109. Matze Lasik Hunter:

    Sometimes, the near term damage reduction potential from climate action is heavily oversold, when it should be clear that this is a long term issue with virtually all the pay-off of any action today and over the next two decades to be found later this century.

  110. Srini:

    That a scientific analysis is being pursued to learn from Katrina is itself reassuring. Man has studied nature scientifically and achieved incredible moon trip, mars mission etc using science. Katrina may or may not have been caused by global worming, but two facts are self evident; one – that taking risks with continued abuse of nature till the abuse is proven guilty may not be a wise policy guaranteed to leave a safe globe for future generations, and, two – intensive research on cause and effects of global worming and on the remedial steps to sustain life harmonious with nature are, today, priority ONE for mankind.

  111. David Tenenbaum:

    Fascinating discussion. The Why Files covered this topic in its most recent edition:

  112. Tom Fiddaman:

    Re #102

    > According to Jesse Ausubel at Rockefeller University, we’re ALREADY decarbonizing the global energy system at a rate that will essentially *eliminate* carbon dioxide emissions by the end of this century:

    Ausubel makes no such claim. In his own writings he says: “… the long-term, global rate of decarbonization is about 0.3 percent per year–gradual, to be sure, but enough to cut the ratio by 40 percent since 1860.” [Liberation of the Environment] That’s a decrease in intensity, not absolute emissions. I think that may be a typo, since he’s quoting Nakicenovic just above. Nakicenovic writes, “The average annual rate of decline is about 1.3 percent, meaning that every year about 1.3 percent less carbon is emitted to generate one dollar of value added. … At an average decarbonization rate of 1.3 percent per year, global CO2 emissions will increase about 1.7 percent annually, assuming the economic growth rate remains about 3 percent per year. … Thus, to stabilize global emissions at some (higher) level in the future, the decarbonization rate would have to at least double to offset the current rate of economic growth.” [Grubler, Nakicenovic & Nordhaus, Technological Change and the Environment, RFF & IIASA, 2002] So, depending on who’s number you prefer, extrapolating decarbonization results in emissions doubling in 26 or 40 years – a far cry from elimination by the end of the century.

    In any case, extrapolation is a risky business. In particular, magical increases in the decarbonization rate are highly suspect given that major reliance on coal is the de facto plan of the US and China in response to limited resources and that major exploitation of gas (e.g. hydrates) is highly uncertain, as is nuclear power.

    If you want to see technology unleashed on decarbonization, try putting a value on carbon.

  113. wayne davidson:

    re 106, Hi William,

    Studying satellite data would say otherwise, is there not an increase in cloudiness in the winter for any Hemisphere compared with summer? RHumidity increases in winter because water vapour density decreases hence more clouds….. GW Models keeping same RH contradict the conclusion that models predict drier air.. Same RH near sea surface perhaps, but not above.

    [Response: I’m not sure about seasonal changes, I was talking about long-term trends deseasonalised. Winter/summer differences are probably due to a slightly different mechanism (guessing) – William]

  114. TCO:

    What are the rules on commenting? Is Steve allowed to come over here and argue points? Why are comments cut off after a certain date of the post (and what is that duration)?

    Response: Anyone can comment as long they follow the comment policy. Discussion closes after a month generally or earlier if we feel it’s necessary. -gavin]

  115. Bernie Masters:

    Excellent interaction between all contributors to this site which I’ve just visited for the first time.
    A recent report quoted in Science (26 August, 2005 – page 1302) refers to a study of the March 2004 cyclone in the South Atlantic that turned into a hurricane and struck the southern coast of Brasil at about latitude 27 degrees south. This was the first hurrican ever reported in the South Atlantic.
    The authors of the report in Geophysical Research Letters state that the hurricane developed because of an unusual combination of high sea surface temperatures, low vertical wind shear and strong mid-to-high latitude blocking which intereferes with normal east-west atmospheric flow.
    As a person living on the west coast of Australia at longtitude 33 degree south, can anyone offer advice on whether I am more or less likely than in the past to have strong hurricanes (we call them cyclones) come this far south?

  116. Tom Rees:

    Re #97. Roger, presumably the losses due to societal changes, increased hurricane wind speeds and rising sea levels will interact. In order to make a rational judgement, you need an estimate of 1) losses with societal changes and no AGW 2) losses from AGW and no societal change, and 3) losses with both.

    Then you need to look at the costs of minimizing AGW, costs of minimizing these societal changes (which are presumably also economically driven), versus the benefits (which, in the case of minimising AGW, are generally considered to be much more than simply reducing storm-related costs).

    Until such an analysis is available, I think that it is pointless conflating these two different issues (societal changes vs AGW). They are not mutually exclusive, after all. It is possible to address both simultaneously. In fact, it may be optimal to do so.

  117. Pat Neuman:

    Re: 108 Mathias, do you think that increases in floods with global warming should be accounted for in developing flood predictions? Potential increases as global warming continues are currently being ignored by government agencies. See Probabilistic Forecast Updates: A Case Study at:

  118. TCO:

    Why do you cut the comments off? I think this is the only thread I can comment on. There are interesting ones in the archives and all. I wasn’t here then, when they were open.

    Has Steve been here? Did you let him comment? Is there a policy that (even if germane to the topic of discussion) one can not link to “anti” webpages.

    Response: Comments are cut off to prevent spam and since people tend to only read recent posts. No one is barred from commenting, but comments are moderated for relevance and tone. If you have comments related to the topic of this post, please continue to comment. Future postings may be more to your taste… – gavin]

  119. Roger Pielke, Jr.:

    Re: #116

    Tom- Good points. Here you go:

    [Note, yes the paper below is in that politically incorrect outlet, Energy and Environment, which is unfortunate, because the paper is solid. Those interested in substance will read it for its merits. Those interested in avoiding the issues can dismiss the paper because of its venue]

    A Climate Policy for the Short and Medium Term: Stabilization or Adaptation?

    Author: Goklany, Indur M. Source: Energy & Environment, Volume 16, Numbers 3-4, July 2005, pp. 667-680(14)

    An evaluation of analyses sponsored by the predecessor to the U.K. Department for Environment, Food and Rural Affairs (DEFRA) of the global impacts of climate change under various mitigation scenarios (including CO2 stabilization at 550 and 750 ppm) coupled with an examination of the relative costs associated with different schemes to either mitigate climate change or reduce vulnerability to various climate-sensitive hazards (namely, malaria, hunger, water shortage, coastal flooding, and losses of global forests and coastal wetlands) indicates that, at least for the next few decades, risks and/or threats associated with these hazards would be lowered much more effectively and economically by reducing current and future vulnerability to those hazards rather than through stabilization. Accordingly, over the next few decades the focus of climate policy should be to: (a) broadly advance sustainable development (particularly in developing countries since that would generally enhance their adaptive capacity to cope with numerous problems that currently beset them, including climate-sensitive problems), (b) reduce vulnerabilities to climate-sensitive problems that are urgent today and might be exacerbated by future climate change, and (c) implement “no-regret” emission reduction measures while at the same time striving to expand the universe of such measures through research and development of cleaner and more affordable technologies. Such a policy would help solve current urgent problems facing humanity while preparing it to face future problems that might be caused by climate change.

  120. Tom Rees:

    Thanks Roger – unfortunately the abstract is a bit low on detail and I can’t access the paper itself. However, one obvious fly in the ointment is this line: “…indicates that, at least for the next few decades, risks and/or threats associated with these hazards would be lowered much more effectively and economically by reducing current and future vulnerability to those hazards…”

    I don’t doubt that, if your horizon is limited to the next few decades, there’s little point in attempting to reduce current GHG emissions. Reducing GHG is a long-term project that at best hopes to achieve stabilization within 50 years. What would be useful is an estimate of the relative cost-effectiveness in, say, 2030 and 2080. That would show how the relative importance shifts according to the time-horizon.

    Furthermore, I don’t see any indication in the abstract of a test for the interaction of factors.

    For example, in your paper, you ascribe the increased costs of storm damage primarily to increased population density and property. By projecting these changes into the future (with a 50 yr time horizon, which again is probably a bit short), you predict that the costs due to AGW will be small compared with the costs due to population changes. You use this result to downplay the importance of emissions reductions. However, if more and more people are going to live on the coasts, then that will in fact make the need to tackle AGW greater, not lesser.

    Furthermore, most authors present a false dichomtomy. Both actions can be undertaken. The question is: “Will each action be cost-effective?” Not “Is one action more cost-effective than the other.”

    One other lesson from Katrina is that adapdation may not be as effective as many pundits propose. After all, the inundation of New Orleans was the one natural disaster that everyone saw coming. And yet even in one of the wealthiest nations on earth the defences were inadequate and the response plan poor. This isn’t a criticism of the federal/state govts – more a criticism of human nature. How much more difficult will it be for developing countries to pre-emtively adapt to a novel environmental situation.

  121. Mark Bahner:

    I wrote, “According to Jesse Ausubel at Rockefeller University, we’re ALREADY decarbonizing the global energy system at a rate that will essentially *eliminate* carbon dioxide emissions by the end of this century:…”

    Tom Fiddaman replied, “Ausubel makes no such claim.”

    Well, you’ll have to take that up with Dr. Ausubel or William K. Stevens of the New York Times. Here is what Stevens wrote in the October 30, 1999 issue of the Times (note: the Solstice environmental website places the date of the article as October 31, 1999):

    “However that may turn out,'”the decarbonization of the energy system is the single most important fact to emerge from the last 20 years of analysis’ of the system, said Dr.Jesse H. Ausubel, an expert on energy and climate at Rockefeller University in New York City. Dr. Ausubel predicts that this evolution will produce a carbon-free energy system by the end of the 21st century.”

    “Dr. Ausubel predicts that this evolution will produce a carbon-free energy system by the end of the 21st century.”

    So says the New York Times.

    Tim Riddaman concludes, “If you want to see technology unleashed on decarbonization, try putting a value on carbon.”

    “Technology” is already being “unleashed” on decarbonization, Tom. That was my very point. The world-wide trend towards decarbonization has been going on for almost 200 years. It started long before any government was ever worried about global warming. It’s not going to stop if governments start paying attention to more important problems (e.g., making sure that no strong hurricanes hit any country).

    By the end of this century, even a “business as usual” scenario puts CO2 emissions near zero…or at least to the point where atmospheric CO2 concentrations are no longer rising.

    In that NY Times article, Jesse Ausubel predicts that the (peak) atmospheric CO2 concentration will be 500 ppm in 2100. That is very close to my own prediction of approximately 560 ppm:

    The current concentration is about 380 ppm. So we have Jesse Ausubel’s (peak) projection of 500 ppm by 2100, and my (peak) projection of approximately 560 ppm by 2100.

    My question for Dr. Pielke (and you, and anyone else) remains…if y’all accept Dr. Ausubel’s and my projections, why is it that, “…we should be taking more effective actions to decarbonize the global energy system.”

    What benefit would be achieved by limiting the peak CO2 concentration not to 500-560 ppm (“business as usual” values), but instead to 450 or 480 ppm?

    This contrasts very strongly with (for example) limiting ***black carbon*** emissions, e.g., from diesel vehicles and residential coal and wood stoves. Black carbon (aka, “soot”) kills.

    Mark Bahner (environmental engineer)

  122. Richard Wesley:

    First off, I want to thank the RC crew for their wonderful site. It is definitely one of the most informative sites on the web and the discussions are also of a high calibre. It gives me some hope for the future.

    I thought the readers might be interested in a page I put up documenting how I managed to reproduce Emanuel’s results for the North Atlantic using the data from National Hurricane Center (also referenced by RealClimate and on the page itself.) For the impatient, the plot is here, and the entire summary can be found here. The pages also includes a few plots I did of hurricane activity for various seasons, including the 2004 season. (Incidentally, we are looking for beta testers for the product used to generate the plots, so if anyone is interested – especially if they have a big pile of data they are trying to look at – please contact me at hawkfish at tableausoftware dot com.)

    Anyway before I go, let me just add that I really appreciate that other scientists (like Roger Pielke, Jr.) join in the conversation here – it really adds to the quality of the presentations.

  123. Paul Emberger:

    Although there is not universal agreement in the scientific community on the global warming and its anthropogenic causes, the political community seems to have accepted it and proposed solutions. My concern is the solutions themselves. For example if we replace significant numbers of internal combustion engines with fuel cells then we trade carbon dioxide emmisions for water vapor. What is the effect of increasing the propoprtion of water vapor in the atmosphere? Is is better or worse than CO2 in terms of the effect on climate. Likewise, what is the impact of diverting significant energy from surface winds with massive wind farms? While we are clearly getting a better handle on climate study, it is not clear that we know enough to start making changes we do not understand or have at least evaluated.

    [Response: You want, at least for a start – William]

  124. Isaac Held:

    Continuing my cautionary remarks about overemphasizing the role of SSTs vs. upper level temperatures in this issue, a useful reference is

    Shen, Weixing, Tuleya, Robert E., Ginis, Isaac. A Sensitivity Study of the Thermodynamic Environment on GFDL Model Hurricane Intensity: Implications for Global Warming. Journal of Climate 2000 13: 109-121

    Part of the abstract reads
    “The results indicate that stabilization in the environmental atmosphere and sea surface temperature (SST) increase cause opposing effects on hurricane intensity. The offsetting relationship between the effects of atmospheric stability increase (decrease) and SST increase (decrease) is monotonic and systematic in the parameter space. This implies that hurricane intensity increase due to a possible global warming associated with increased CO2 is considerably smaller than that
    expected from warming of the oceanic waters alone.”

    I am harping on this point becuase i see it a central to an informed discussion of the relative ability of internal Atlantic SST variations and global warming to affect hurricane intensity: an internally generated increase in Atlantic SST is likely to be associated with a more unstable atmosphere than the same increase due to global warming.

  125. Steve Bloom:

    Re #120: Five years is a long time in climate science. I think (Knutson & Tuleya 2004), cited in the post and the source of the first graph, is more reflective of current thinking. Note that it uses an ensemble of models as contrasted to the single one used in the study you cited.

    You can use Google Scholar to try to check if a paper is still entirely current. Unfortunately, sometimes it’s a bit hard to figure out if this is the case or not since often the terms of rejection of the prior work are subtle.

  126. Lynn Vincentnathan:

    RE #118, I see no problem with your suggestions. I hope you are aware of Amory Lovins’s works, such as NATURAL CAPITALISM, and works of other such experts & businesses that have actual examples of greatly reducing GHGs in cost-effective ways. As I’ve mentioned I’m just waiting for a plug-in hybrid, then I can drive almost entirely on wind power, and probably at a cheaper price.

    I think that building stronger buildings & higher levees actually costs more, but will be worth it in the long run if destruction from hazards is mitigated. On other hand, we can also build using “green” products (like reused wood, and natural pozzalons in cement), or planning room/building sizes to available materials (without much wastage), and using passive solar & other energy/resource efficient/conservative techniques & products. If we have to rebuild, let’s do it right this time, with awareness of most likely to worse-case GW scenarios. It seems the science keeps racheting up predictions of GW harms as time goes on – compare FAR, SAR, TAR & the one coming up. We’ve got to be aware of what way the wind it blowing.

    I think congress wanting to open up more oil drilling in the Gulf of Mexico is very unwise, considering we are entering a period of greater natural hurricane activity, plus the overlay of GW enhancement, perhaps even category 6 sometime in the future. Maybe they really do not know about GW.

  127. Roger Pielke, Jr.:

    Re: Response to #97


    Thanks for your continued comments, and my apologies if you interpret condescension and insinuations, none are intended. I will admit to pushing you to engage this discussion in the context of a robust literature on climate impacts. That literature does suggest some answers and raise some further questions. Most importantly to your latest point, how does one explain the fact that the same hurricane damage record shows a clear and statistically significant ENSO signal (in relation to ASO Nino 3.4) shows absolutely no correlation with the Atlantic annual PDI? This question must be addressed satisfactorily before asserting a future relationship of PDI and damage. And until the PDI is shown to be a metric of “destuctiveness,” forward-looking statements about the relationship of changes in the PDI to changes in damage remain purely speculative.

    FYI, as interesting as this thread has been, it is becoming a bit difficult to follow. Perhaps you might revisit this subject when Webster et al. comes out later this week, which will have a little something for everyone.

  128. Matthias Brun:

    RE # 117 Pat: Flooding is definitely an issue in Europe and also Landslides an avalanches once you get to steeper terrain. In Switzerland every community has to develop a map of natural hazards-
    which is relevant for buildung actions. So if you want to build a new
    house on the wrong slope you are either not allowed or you have to get further inquieries. I work in an office for natural hazards and I can tell you we got a lot of work right now because of the recent flooding event here. In certain areas boulder of 15 feet in diameters where transported in small riverbeds – and you can imagine the damage to the houses.
    The events we got in some place were a lot bigger than the 300-year-incidents we calculated our hazard maps with. So as you can figure out easely the statistics have to be rewritten or don’t work anymore under the changing climate!! Extrapolation and modelling of rainfall events is all you can do – and the picture doesn’t look good. All you can do is abandon some of the dangerous areas in the moutains or along the rivers – not very easy in the highly populated alpine regions in Europe.
    Same problem for New Orleans. Climatic change is taken as a fact in Europe. And I still think the discussion should be on values and human duties for gonverments and everyone and how to attain the inescapable post fossil society instead of technical and security measures
    because that is closing the eyes to origin of the problem.

  129. Tom Rees:

    Re #127, Roger, you ask: “how does one explain the fact that the same hurricane damage record shows a clear and statistically significant ENSO signal (in relation to ASO Nino 3.4)”

    Have you ruled out the possibility that ENSO changes the storm track, such that it is correlated with the proportion of landfalling storms (as well as hurricane intensity). If this were so, then it would explain why it is a better correlate of economic loss than storm intensity alone. I have skimmed your paper, but can’t see where this issue is addressed.

  130. Joel Shore:

    Re #123:

    (1) While it may be true that there is “no universal agreement” in the sense of complete unanimity in the scientific community on global warming, there technically isn’t that on evolutionary theory or just about anything else. There is a general concensus and, while uncertainties remain, I think that at least here in the U.S., the politicians are actually well behind the scientists, not ahead of them, in their acceptance of the science and willingness to act on it.

    (2) As you can find discussed in a previous post here on RealClimate, direct anthropogenic emissions of water vapor are basically a “red herring” in the context of global climate change. First of all, fossil fuels are hydrocarbons and hydrocarbons contain hydrogen that gets converted to water vapor upon combustion, so our current fossil fuel burning is already producing plenty of water vapor. Second of all, humans can’t easily have nearly as significant effect on water vapor in the atmosphere as carbon dioxide by direct emissions of these gases. This is because the time scales for the gases to remain in the atmosphere are much different. (A CO2 perturbation lasts on the order of a hundred years or more while water vapor gets rained out in about a week.) It is also because there is much more water vapor in the atmosphere than CO2 and, since the amount of climate forcing goes approximately logarithmically with concentration that means the concentration of water vapor has to change by a significantly larger ABSOLUTE amount to produce the same effect. (Admittedly, a given FRACTIONAL change in water vapor concentration is more potent than the same FRACTIONAL change in CO2 concentration but this difference is not large enough to offset the larger difference due to their relative concentrations in the atmosphere.) Where water vapor is important is as a feedback effect…whereby the warming of the atmosphere due to increased CO2 causes the “equilibrium” concentration of water vapor to increase and this then enhances the warming because of water vapor’s absorption of infrared radiation.

    (3) Without having done the calculation (or seen it done), I would conjecture that your concerns about wind are another red herring. The amount of wind farms needed to extract a noticeable amount of the total energy available from the wind would probably be huge. Furthermore, the perturbation to the winds that we cause with wind farms will, at least for quite some time, likely be smaller than the perturbations just due to other structures that we have built (buildings, etc.)

  131. Roger Pielke Jr.:

    Re: #129

    Tom- Thanks. Actually this paper is more directly relevant:

    Pielke, Jr., R.A., and C.W. Landsea, 1999: La Nina, El Nino, and Atlantic Hurricane Damages in the United States. Bulletin of the American Meteorological Society, 80, 10, 2027-2033.

    We do find that the ASO Nino 3.4 index is related independently to both frequency and intensity. With respect to the latter we find that a 20% difference in intenstity (36.3 m/s vs. 30.6 m/s average winds) between the two phases manifests itself in twice the losses per storm during La Nina than in El Nino, and we can see this effect in the seasonal totals. So, yes, we can identify the changes in the damage record related to intensity that are considerably smaller than those identified in the PDI.

    Rick Katz quantified these effects more rigorously in this paper:

    Katz, R.W., 2002: “Stochastic modeling of hurricane damage.” Journal of Applied Meteorology, 41, 754-762.

    [Response: Just a clarification: a 20% increase in wind speed (as cited above) corresponds to a 73% increase in the cubed wind speed. The PDI is the cubed wind speed, integrated over surface area and life-time of a hurricane. If size and life-time of hurricanes increase as well with increasing mean wind speed, then the PDI will increase more than 73% for a 20% increase in wind speed. What I conclude from this:
    – A doubling in losses for a 20% wind speed increase seems consistent with losses being proportional to the PDI.
    – You don’t know whether the ENSO related changes in hurricane power that you can identify are indeed “considerably smaller”; rather they are similar in magnitue to the changes that Kerry talks about.

  132. Roger Pielke Jr.:

    Re: #131


    Let’s assume that you are correct that the ENSO-related and PDI-related effects on TC power are of similar magnitude (but do note that Emanuel uses max winds and I referred to mean winds). The question remains, if this is the case why do we see a very strong ENSO signal and no PDI signal in the damage record?

    [Response: This is just two bits of speculation on my part, but it is conceivable that a) the influence of ENSO is of a different character than the influence from SST (i.e. there is more happening than a similar increase in hurricane intensity/number), and ii) the different frequency distribution of ENSO events compared to variations in SST (or PDI) mean that the signal is stronger compared to the noise in that frequency band. i.e. the SST influence maybe harder to discern in the data because of the coastal development contamination which clearly dominates the longer timescale changes. -gavin]

  133. Steve Bloom:

    A quick Google Scholar finds . If this paper is correct, the upshot is that ENSO does have a major impact on tracking of hurricanes, and thus on the damage they do. (Interestingly, there’s a related paper showing that ENSO does the same thing on the other side of the planet with East Pacific typhoons — that’s one dominant cycle!) I think Emanuel addressed why it might be a long time (50 years) before any connection between PDI and damage would become apparent.

  134. Steve Bloom:

    From Emanuel’s FAQ:

    7.) Q: Does this [increase in PDI] mean that we are seeing more hurricane-caused damage in the U.S. and elsewhere?

    A: There is a huge upward trend in hurricane damage in the U.S., but all or almost all of this is due to increasing coastal population and building in hurricane-prone areas. When this increase in population and wealth is accounted for, there is no discernible trend left in the hurricane damage data. Nor would we expect to see any, in spite of the increase in global hurricane power. The reason is a simple matter of statistics: There are far too few hurricane landfalls to be able to discern any trend. Consider that, up until Katrina, Hurricane Andrew was the costliest hurricane in U.S. history. But it occurred in an inactive year; there were only 7 hurricanes and tropical storms. Data on U.S. landfalling storms is only about 2 tenths of one percent of data we have on global hurricanes over their whole lifetimes. Thus while we can already detect trends in data for global hurricane activity considering the whole life of each storm, we estimate that it would take at least another 50 years to detect any long-term trend in U.S. landfalling hurricane statistics, so powerful is the role of chance in these numbers.

  135. Roger Pielke, Jr.:

    Re: 132 and 134


    The data has been adjusted to remove any development signal. But I do lean toward a view that the relationship is weak, for whatever reason (and there are good ones why this might be so).


    My question seeks to address how Kerry’s explanation can be correct, yet we still can identify and ENSO signal in the database. There only only a few possibilities, and Kerry’s simply reinforces the argument that the PDI is only weakly, if at all, related to damages.

    [Response: Detecting a trend and detecting an oscillatory signal of the same magnitude in the same noisy data set are not the same thing – I suspect finding the oscillatory signal is easier. This would be easy to check for anyone with a couple of hours time at their disposal (unfortunately, that’s not me right now). Cheers, Stefan]

  136. Pat Neuman:

    Re: 128 – Hi Matthias, there’s a commentary on the overtopping of dikes in New Orleans and Grand Forks at: … and at:

    Flood prediction, preparedness and design of structures with a rapidly warming world interests me. If you want to talk more I suggest you join:

  137. Steve Bloom:

    Roger, Stefan (among others) has already responded to the same issue in comments 49, 73 and 82 in considerable detail. The key point seems to be that ENSO affects tracking and PDI does not. According to the paper I linked, ENSO results in more “straight-moving” hurricanes that track through the Caribbean and Gulf before landfalling. This seems to me to be a very large effect since pretty much all of those hurricanes landfall, many of them in the US, plus (I assume) they tend to be a lot stronger when they do so since they spend more time over warmer waters. Stefan’s view is that PDI could already be having a substantial but still undetectable influence, so perhaps it would be worth looking at how strong of a signal could exist now and remain undetectable. I assume that this must be the calculation Emanuel did in coming up with that 50 year number. Would it help resolve things to have that?

  138. Tom Rees:

    The Association of British Insurers use an Insurance Catastrophe Model to estimate that a 6% increase in hurricane wind speeds will increase the annual insured losses by $3.9 billion in the US and $1.6 billion in Japan (2004 $). For a 1-in-100-year storms, the cost will be an extra $41 billion in the USA. This assumes that there are no changes in demographics, precipitation, storm surges or adaptation. They point out that, on the one hand, higher insurance premium will encourage more risk-conscious development but that, on the other hand, increases in precipitation and storm-surge height are also likely and will inflate the figure.

    I know insurers have an incentive to talk up risks, but they don’t have an incentive to talk up risks due to climate change compared with other risks. In this regard, this Sept 8 report (coauthored by a paid-up scientist from LLNL) is interesting Availability and Affordability of Insurance Under Climate Change. They quote one of your papers, Roger! “One can easily hypothesize that increasing population and urbanization in the United States has led to a commensurate increase in population at risk. Yet, one can also hypothesize that the various societal responses may have more than compensated for population growth and in fact fewer people are today at risk.” ;)

  139. Roger Pielke Jr.:

    Re: 137

    Steve- Thanks. We do find an independent intensity effect in the ENSO results, so we can simply ignore the frequency effects for present purposes, and the question remains. Emanuel’s analysis suggests that PDI is not at all a good proxy for damages, i.e., there is historically no relationship with damages, and in the future this relationship will continue to be weak. (Another way to think about it is that the PDI includes a whole lot of information not relevant to hurricane landfalls, so of course the relationship to damage is weak.) The ENSO analysis helps us to understand what magnitude of climate signals might be observed in the damage record via a simple climate index. What this suggests to me is that climate scientists should continue to develop indicies of hurricane behavior, but to use as one criterion for their development a close correlation with damages. Emanuel’s work is an important step in this direction, but I’d bet we can improve upon it. We have discussed using V^3 at landfall as such an index, but it is not well correlated with the annual/basin PDI. The ACE index is similarly poorly correlated with damages. But let’s keep looking, the search really has just begun. There is no need to force the PDI to carry more significance than the data allow, there are going to be better indicies from the standpoint of understanding the relationship of climate changes and damages.

  140. Tom Rees:

    Re #137 Roger, are you really saying that, when a hurricane hits land, there’s no relationship between PDI and likely destructiveness?. I presume not. After all, we know that a mean 20% increase in wind speed in La nina years gives a doubling of damage per hurricane Pielke & Landsea, 1999.

  141. Dan Allan:

    The debate here has focussed on two issues:

    1) correlation between SST and hurricane strength / PDI.

    2) correlation between PDI and damage.

    Obviously, both of these correlations need to exist to conclude that AGW will lead to increased hurricane damae.

    Regarding the 1st point:

    I admit that, like most of the rest of us, I am not an expert on hurricane formation. But it seems quite clear empirically that the SST correlates much more closely with hurricane strength than does temperature gradient / instability. For instance, it is well known that hurricanes require SSTs of ~80 degrees F to form. Period. This is the minimum. There is no exception in the case of a very high degree of instability, or very low shear, or whatever, where a hurricane will form with a SST of 76 degrees F. It simply doesn’t happen. Moreover, each category of storm has a similar minimal SST under which it will form. I wish I had a link for this, but I can tell you that I have read enough hurricane forecast discussions to feel certain of what I am saying. This suggests to me, personally, that a correlation between AGW and hurricane strength / PDI, is highly likely – unless someone can show an additional likely effect of AGW that is so strong that it cancels this factor out entirely.

    Regarding the second point:

    In some cases, it seems to me that the argument in favor of a correlation is so strong that, if we don’t see a correlation historically, we have to simply wonder if there is enough data yet to see the correlation, if we are asking the right questions, if there is so much background noise that it masks why is potentially a very significant correlation – or some combination thereof. I think this is just such a case.

    The issue of how we pose the question seems especially pertinent here. Unless I misunderstood, Roger is looking at total annual PDI versus annual damage, rather than each storm’s PDI versus that storm’s damage. To me this is likely to obscure correlations with lots of noise. Suppose we wanted to test the correlation between pitching velocity and strikeout potential. Would we look at the net average velocity across all pitchers in year A, and compare it to total strikeouts? Or would we look at the average velocity of each pitcher and compare it to that pitcher’s strikeouts? To me, the first method has a great deal of noise inherent in it.

    Finally, if Katrina really causes 200 billion in damage, and given that it was strong storm in a year of strong storms, it is likely to bring out a correlation between PDI and damage that had not previously been evident. And the fact that a single event could do this (assuming it does do this) is just an indication of how few data points we have.

  142. Tom Fiddaman:

    Re #119 (A Climate Policy for the Short and Medium Term: Stabilization or Adaptation?)

    I don’t have the journal, but assume the article is similar to this one by Goklany: Reducing Climate-Sensitive Risks in the Medium Term: Stabilisation or Adaptation?. I agree with some of Goklany’s observations, e.g. if you want to stop malaria, tackle it directly, not via climate. However, in other ways it’s shaky, including those observed by Tom Rees (#120, the false dichotomy, short horizon, interactions).

    Pielke writes, “There are much, much better ways to deal with the threat of hurricanes than with energy policies … . There are also much, much better ways to justify climate mitigation policies than with hurricanes … .” (#46). By contrast, Goklany seems to conclude, “there are better ways to deal with malaria than climate policy, so let’s work on malaria and skip the climate policy for now.”

    Kyoto is used as the usual straw man. But Kyoto fails conventional cost-benefit tests because it’s inefficient, not because emissions control is inherently a bad idea. The low payoff to Kyoto in conventional analyses is also contingent on discounting the welfare of future generations, hardly a forward-looking ethical policy. If you don’t do that, Kyoto looks like a good deal, and more efficient measures really pay.

    Fundamentally, if avoided emissions have a value, we ought to impose it uniformly now. It’s hard to imagine how one would “broadly advance sustainable development” without doing so. To think there’s no value to avoided emissions requires some rather extreme views on the distribution of impacts and reversibility of emissions vs. investments.

    If you don’t put a value on carbon, market forces will overwhelm the no-regret and technology policies Goklany proposes by redirecting them to business-as-usual purposes. Witness that vehicle technology has advanced greatly since the 80s, but absent policy, fuel economy has slightly declined, driving has increased, and vehicle power/weight ratios are way up.

    In a similar letter to Science Goklany suggests:
    Thus, it would be far more beneficial, and cost-effective, at least for the next several decades, to reduce vulnerabilities to current problems, especially if they might be exacerbated by climate change (e.g., hunger, malaria, drought, and flooding) (3). Even with a lagtime of 50 years to account for the inertia of the climate and energy system, the aforementioned analyses suggest we may have at least a quarter century window (2080s minus 50 years) before deciding on the depth and extent of mitigation. Meanwhile, we should focus on improving mitigation and adaptation technologies and our knowledge of climate change science, economics, and responses. This way we can advance sustainable development and solve the problems of today while furthering our ability to solve the problems of the day after tomorrow.

    Goklany’s compression of the time constants of the economy and climate to 50 years is rather extreme given infrastructure and power plant lifetimes on the order of 40 years, carbon cycle time constants >100 years, and long adjustment times to radiative imbalance. Goklany’s suggested “wait and see” approach doesn’t produce good results in a system with long delays.

    Perhaps a better approach would be to look for synergies between near and long term measures, e.g. land use policies that put people out of harm’s way and lower transport energy intensity, or recycling carbon tax revenue into disease prevention.

  143. wayne davidson:

    I’ve noticed Katrina and Orphilia’s ocean path speeds, fascinatingly slow, Is this normal? Or is there a record of ocean path speeds to compare them with? I would suggest that there is no t enough continental cold air generating dominant winds to cary systems at more “normal” speeds. This abnormality would explain Katrina’s intensity cauused by significantly warmer SST over the gulf of Mexico, and also would explain Orphilia’s longevity, over somewhat cooler sea surface temperatures .

    The answers we seek, seem to be right in front of us, and SST’s have a direct impact as explained by Orphilia’s weaker winds.

  144. Roger Pielke, Jr.:

    Lots of good comments here, a few quick replies,

    Re: #138

    Tom- On the ABI report, see this post:

    And the quote that Mills et al. cite comes from a 1999 paper and refers to floods. It is true that there are no studies (at least that I am aware of) that quantify trends in floodplain occupancy or trends in wealth in floodplains, so in that paper we used overall trends in population and wealth as proxies. But were I a betting man I’d be “all in” on the first hypothesis!

    On their discussion of attribution, see this post:

    Re: #140

    Tom- Emanuel (2005) focused on the PDI as measured on an annually accumulated basis. The PDI at landfall doesn’t quite make sense because the PDI integrates the max winds (cubed) with the lifetime of the storm. I suppose we could define landfall as a period of time when the storm begins to have effects on land to when it moves on and calculate the PDI over that time. I would fully expect that such an index would be strongly correlated with damage, conditioned upon the population/wealth at risk in the path of the storm. This is exactly the sort of research that ought to be done.

    Re: #141

    Dan- Be careful directly comparing estimates of Katrina’s damages with other historical storms, it is not yet clear what the apples to apples number should be, we are working on this and hope to have some recommendations this fall. Meantime, see these posts:

  145. Lynn Vincentnathan:

    RE #141, the social sciences use (I think it’s called) “structured sampling.” If they understand that, say income, has an impact, and they are not likely to randomly draw enough folks from a particular income bracket (proportionate to their percent in the population), then they will arrange to have the same percent of each income group in their sample as in the population.

    I also vaguely remember reading about Love Canal, and the official studies found no significant correlation between ill health & living in Love Canal (partly due to low numbers), but when a resident along with some university scientists found an old geological map of the natural swale network underlying the community, and added that variable into the study — finding that most of the sick people lived along the swales — they got a high and significant correlation. They also tested the soil in the swales and found greater toxicity.

    So, of course, we have to compare PDIs only of hurricanes that make landfall in roughly the same population/built areas, to see if PDI correlates positively with damage (I think this is a no-brainer). Then we have to see whether greater PDI has been caused by natural causes, random & unpredictable fluctuations, or perhaps in part by AWG.

    The problem now seems to be that we can only talk about hurricane PDI on the whole for the entire world, but if we ever get to a point where we can figure what (including AGW) went into each hurricane’s PDI (including what went into SST in its vicinity), then we’d be able with more confidence to attribute a portion of the damage from specific hurricanes to AGW.

    I’m not sure, but is it correct to say that it is just as likely as not that AGW increased Katrina’s PDI and the damage (without hazarding to guess by how much)? That’s the way I plan to put it, unless someone here says that’s a wrong assessment. I also say that AGW has increased hurricane intensity in general, and is expected to increase it more so in the future, perhaps giving us even Category 6 hurricanes.

    I think there are several AGW factors & other natural factors that go into higher Mexican Gulf SST, and we need to consider all of them – more shallow waters being heated more, & more rapidly than deep seas; the slowing of the thermo-haline ocean conveyor from fresh water pouring into the North Atlantic, leaving hot waters more stuck in place in the south.

    Personally, my gut feeling is the Gulf waters were heated by AGW more than the .5 degree average for world SST (which I think is averaged for the whole year, so even particular times of year may have greater warming from the greenhouse effect). I think they said the Gulf SST when Katria struct was 6 or 7 degrees F(or C ?) higher than usual. I’d wildly guess maybe two-thirds of that was from natural fluctuations, and maybe a third from AGW factors (direct & slowing of the thermo-haline).

  146. J. Sperry:

    Re #143:

    I followed the links in #122 above, and found an abundance of data on ocean path speeds of storms measured at 6 hour intervals. The mean ocean speed is 12.9 mph, with a st. dev. of 8.7 mph, and the data can be summarized as follows:
    0-5 mph, 19% (0.5% were 0, i.e., stationary when measured)
    5-10 mph, 27%
    10-15 mph, 24%
    15-20 mph, 16%
    20-90 mph, 14%

    I’m not having luck finding data on the ocean path speeds for the recent storms (maybe 15 mph for Katrina and 7 mph for Ophelia), but I doubt that they could be considered “fascinatingly slow” or “abonormal” since one fifth of the measurements are below 5 mph (a slow jog in human terms).

  147. Hank Roberts:

    Katrina passed over and picked up heat energy from a 200-foot-deep “loop current” that’s tracked in the Gulf every year, containing warmer water — so the hurricane pulls up warm water instead of cold water as it travels across that area.

    QUOTE (from befor the storm came onshore)

    “Katrina could turn out to be the perfect hurricane, much to the dismay of south Louisiana residents.

    Not only is there little to keep it from strengthening on a dangerous scale, but it is expected to create a dome of storm surge that could flood much of eastern New Orleans, the 9th Ward and Mid-City in New Orleans, swamp much of the West Bank and Plaquemines and St. Bernard parishes, and flood north shore areas.

    “I don’t remember seeing conditions as favorable as this for a strengthening hurricane for a long time,” National Hurricane Center Director Max Mayfield said Saturday.

    He was referring to a unique combination of physical and meteorological conditions that are expected to cause Katrina to spin up to Category 4 or 5 strength, like a top accelerates when you pull its string.

    The northern Gulf of Mexico is unusually warm, rising past 85 degrees this year. And while that could, in part, be due to less cool freshwater entering the Gulf from the Mississippi River, National Hurricane Center meteorologist Eric Blake said it’s more likely the result of relentless high temperatures in recent weeks along Louisiana’s Gulf Coast.

    ****** That warmth extends more than 200 feet deep in one area in advance of Katrina, thanks to a donut-shaped pool of hot water called the loop current, which breaks off from the Gulf Stream and floats around the Gulf each year. ******

    The warm water acts like a flame, heating the atmosphere above it. In this case, that atmosphere already has formed into the circular system of thunderstorms that make up a hurricane.

    Above the storm circle, an upper-level high-pressure system helps squeeze out the rising hot air, a process called outflow, which increases the wind speeds and keeps the storm healthy.

    Pressure builds

    Not present near the hurricane on Saturday were two things that could reduce its intensity: wind shear caused by upper-level disturbance blowing across the cloud tops and reducing their warmth and height; and dry air that could swirl into the circular storm and sap it of the moisture needed to keep it strong.

    And by Saturday, Katrina had grown so large and strong that it had begun entering what’s known as an “eye-wall replacement cycle.”

    As a hurricane spins counterclockwise, the clouds at its center move faster and faster in a circle, which narrows until it falls apart, to be replaced by a new circle of eye-wall clouds.

    The eye wall contains the hurricane’s highest winds, and as the inner circle collapses, those winds can decrease a bit. But with the collapse happening Saturday, it provides an indicator that the wind speeds will increase today.

    The result, Mayfield said, is that Katrina is expected to be a strong Category 4 hurricane, with winds of 145 mph, as it approaches Louisiana’s coastline Monday morning.

    Researcher Ivor van Heerden warned his model is probably understating the water’s effects, though. The surge will be topped by wind-driven waves that could be half again as high as the surge, which could mean water pouring over levees all along the south shore of Lake Pontchartrain.

    ‘A worst-case scenario’

    All of eastern New Orleans outside the levee system, including the Irish Bayou community, will be underwater.

    . . . . . . .

    Mark Schleifstein can be reached at or (504) 826-3327.

    © 2005 The Times-Picayune. All rights reserved.

  148. Pat Neuman:

    Re: 147 That’s interesting data on ocean path speeds. Do you have any ideas for making a table on hurricane size? e.g. a table showing average annual max diameter for Atlantic-Gulf hurricanes.

  149. Gerald Machnee:

    Re #145 – in the last paragraph. Guessing at fractional contributions of AGW is not good science. I did find the quotes in #147 very interesting as I had heard most of them as Katrina was approaching. It does shed light on why Katrina was that strong – almost all factors coming together.

  150. wayne davidson:

    re 147, Although helpful, my fascination was not based on those stats you just gave.

    What is Interesting is two hurricanes having roughly close points of origins , lets say on average slowish (if these stats are right), but at times nearly stalled or looping , abnormal perhaps? Both hurricanes having plenty of time to strenghten over warmer water, but one, Orphilia languishing longer over a little bit cooler water.

    This comparison shows with ease that SST’s are proportional to intensity, Katrina at landfall being a Cat 4 vs Orphilia’s Cat 1. It is better to compare individual events, one on one. instead of bunching them up in a de-personalyzed lump of statistics which looses meaning traction.

    The path speed of Katrina seemed slower at times, especially before hitting the Florida coast.
    But, I am intrigued by two consecutive hurricanes at slowish speeds, in large measure with many other world wide weather systems stalled, stalling or slow, may I give the example of that Cyclone hanging for several weeks North-East of Boston this past May giving all this cool rain. The challenge for stat analysts, is to find data contradicting the Hurricane comparison cited above.

  151. Steve Latham:

    Hi, I’m in a hurry but wanted to ask about societal adaptation (or some such phrase) that in part counters the increasing damage expected from hurricanes, etc. If this adaptation is to be used as an argument to suggest that AGW is not increasing costs in damage or loss of life, then I think there would have to be some accounting of the costs of that adaptation. I’m sorry if I’ve misuderstood, and if I have please correct my misinterpretation. Assuming that some index of damage remains flat, it seems to me that if money was spent on better levees, better pumps, more resistent construction (rather than on something else) in part to ameliorate climatological impacts, if the index ignored those expenditures then that metric is not a good one. In fact, if new technology is brought to bear on the problem because it should provide an improved solution, the cost of the climate change or whatever should in part be measured by the amount that the damage was not reduced as it should have been. This is a poorly-worded way of challenging the idea that we should make comparisons to a fixed baseline. I realise that you’re not comparing to a fixed baseline (because you account for increased population and investment in the affected coastal areas), but Dr. Pielke can you answer regarding whether the costs of adaptation are fully accounted? Thank you.

  152. Roger Pielke Jr.:

    Re: 151

    Steve- Thanks. This is a good question. But the available data actually suggests the opposite effect. Society was arguably less vulnerable in historical times than today. For example, surveys of damage conducted after hurricane Andrew found that homes built more recently experienced more damage. This makes sense if you consider that in the past there was less insurance availability, much less federal disaster assistance, etc. So people had to build in ways that were more resilient. An important “adaptation” to disasters has simply been to become more wealthy as a nation. The federal aid following Katrina could not have occurred in 1900, 1926, 1938 etc. Scholars debate whether programs such as the National Flood Insurance Program have resulted in decreased or increased losses. We have discussed here the challenges of identifying a climate signal in disaster trends, but identification of policy signals is equally as challenging. I think that the balance of evidence suggests that adjustments of past losses are likely underestimates, perhaps significantly so, of what the same storms/events would result in today. But like any other complex issue, more research would be a useful contribution to this relevant, but under-studied area.

  153. Tom Rees:

    Re #144 – now I understand the problem with the PDI! Thanks Roger.

  154. Paul Emberger:

    Re 130
    Thanks for the explanation of the differences between the effects of CO2 and H2o vapor.

    However, with regard to wind I believe the jury is still out. See
    for the only study I have been able to find on the possible effects of wind power on climate. There seems to be enough evidence to indicate further study is needed. It appears that there is definitely some effect (and it may even be positive vis a vis greenhouse gases).

    I am concerned about politicians jumping on “solutions” for parttially understood problems with consequences that are not known or considered. Most solutions WILL have impacts on the global economy (not talking business, here, but distribution and exchange of goods and services inherent in human societies.) The fact that wind is renewable and “clean” makes it attractive but not necessarily safe. From a systems perspective I would like to see more risk analysis of the climate problems exacerbated by human activity as well as the solutions available.

  155. Joseph O'Sullivan:

    This thread is an interesting foray into the intersection of science and regulatory policy.

    We cannot expect too much from the scientific community in the policy / regulatory arena. Directing research to answer policy questions has some merit but it also has limits. Research should not be overly focused on supporting policy decisions. There is not a straight path to scientific discoveries. Undirected research has value even if it might bring up unforeseen policy implications and might be controversial or distracting.

    In regulatory decisions one’s theory, research or publications might not receive the attention the author wants or deserves, but it is naive to think that the most accurate information will always be translated into regulations. Environmental law and regulation making is a very messy process.

    Roger some of your comments can be pretty confrontational, but others are more accommodating, its kind of a “good cop – bad cop” thing. More good cop and less bad cop would be better ;)

  156. Tom Fiddaman:

    Re #121 (Bahner on Ausubel, etc.)

    Thanks for the links – they make Ausubel’s forecast clearer. His logic is fuzzy though.

    Ausubel’s position requires invoking a jump in the decarbonization rate from 0.3%/yr observed in the past (his number) to something well above the growth rate of the economy. If we pretend that the current energy system is all coal, a total shift to gas this century would only get you about 2%/yr decarbonization – still way too slow.

    Since he’s not optimistic about renewables and efficiency and places nuclear far out on the horizon (here) sequestration would have to play a big role, and he writes about zero-emission power plants. But why would anyone build a ZEPP (e.g. coal IGCC with sequestration at 45% efficiency and $2000/kW vs. plain IGCC at 55% and $1200/kW) if the price of carbon emissions is 0?

    The economy in the past has not been pursuing decarbonization. It’s been pursuing economic gain, and realizing decarbonization as a side-effect. The coal-oil transition was driven by liquid fuel convenience. The oil-gas transition is happening mainly in the power sector due to lower gas cost and high CCT efficiency. But there are reasons to think those trends won’t continue. A large share of future gas may be used for upgrading coal and heavy oil for transport fuel. Coal could easily expand its role in the power sector. Since hydrogen is a carrier, not a source, it doesn’t fundamentally change the outcome, unless its source is carbon free. But again, if you’re making fossil H2, it’s easier to vent CO2 than sequester it.

    Finally, even if Ausubel is right and decarbonization magically jumps from 1 to 5%/yr with no policy intervention other than R&D, that might not affect the marginal product of avoided carbon emissions much because the logarithmic concentration-forcing relationship offsets the ~exponential forcing-damage relationship. So, carbon will continue to have a value, and ought to have a price.

  157. Lynn Vincentnathan:

    RE #147, and the loop-current & gulf stream, have these been (or will these be) impacted by AGW in any way – say, increasing the SST?

  158. TCO:

    Thanks for previous responses (sorry to ask twice): new questions (sorry not sure how to ask it except hitting the one thread that is open). What is a good source to explain the very basics of radiation effects of how greenhouse gases trap heat? For instance, do greenhouse gases vary in their effect based on if sun is shining or not (day versus night, also polar summer, winter). Do they vary in their effect depending on the temperature of the surface? I am an anti-person (i.e. evil) however I think this area is really one where my question is not leading to a gotcha, but just to understanding the unarguable basic physics.


    -evil anti-person ;)

    [Response: Try here or here or here. The answers to your questions are not much (but it depends) and yes. -gavin]

  159. Eli Rabett:

    Gavin I must say, here and here are complete apples and oranges but here (the one in the middle from uchicago) is right on with a caveat). The VUV (<200 nm) absorption due to the O2 Schuman Runge bands essentially wipe out all of the radiation that would be absorbed by methane/CO2 and water vapor as discussed in the here and here. The stratospheric ozone layer takes care of most of the deep UV (<300 nm), so that it has very little flux through the troposphere, and thus very little absorption and thus very little direct effect from sunlight. Thus the comments in here and here are mostly besides the point, because there is no VUV or UV in the regions where greenhouse gases can absorb.

    The uchicago here, rightly place the emphasis on absorption and reradiation of IR emission by the greenhouse gases. The caveat is that these molecules can weakly absorb sunlight in the near IR and visible on combination and overtone bands, mostly of water vapor, and on weakly absorbing forbidden transitions such as the Chappius bands of ozone, and for very low concentrations of dimers. See (at the bottom) where the lower limit contribution of the visible absorptions of water vapor between 550 and 600 nm are estimated as ~ 0.2 W/m2 (~peak of the solar spectrum) For something a bit more esoteric

  160. Joseph O'Sullivan:

    The new paper on TCs and climate change is out
    I have internet access to it but I don’t have a subscription. Having given it a quick review the conclusions seem similar to Emanuel’ s paper.

  161. Gerald Machnee:

    Re #160 – The paper seems to cover a 35 year period beginning in the 1970’s. Considering that ocean temperatures have cycles lasting several decades, this study does not give any suprising results. Why not try a 35 year cycle that ends in the 1970’s? Would that show a decline and indicate why there was so much building in hurricane prone areas?

    [Response: There is no evidence to support the existence of a multidecadal cycle that influences global mean tropical SSTs. So while one might speculate that some of the changes in tropical Atlantic hurricane statistics could be related to cyclic changes in climate (i.e., the AMO), it is very difficult to argue this for hurricane statistics in other ocean basins, let alone global average hurricane statistics. As discussed in our posting above, Emanuel’s analyses also cast doubt on the proposition that the recent Atlantic basin trends can be dismissed as simply part of multidecadal cycle alone. -mike]

  162. Tom Rees:

    Webster’s study is based on satellite imagery, so only data for the past 35 yrs is available. But all you can ask of a theory is that the available data are consistent with it. So it’s interesting that these data don’t support current theories – the increase in intensity is greater than the theory predicts. So either there’s something else going on or the theory is wrong. “And modeler Thomas Knutson of the Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey, says, “We would not have expected the signal [of storm intensification] to be detectable at the present time,” based on theory and his modeling of storms under a growing greenhouse. That, he says, prompts the question, “Are these trends real?”

  163. Stephen Berg:

    “Hurricanes Are Getting Stronger, Study Says”:

    Since the Saffir-Simpson rating system is a wind strength-based scale (unlike the Fujita Scale for tornadoes, which is a damage-based scale), the increase in human inhabitation along the coasts of the Gulf of Mexico and the western Atlantic Ocean does not figure into the number of Category 4s and 5s.

    What is startling is that this increase in inhabitation is happening while the danger to coastal residents is rising. It is like people are blissfully ignorant to the consequences of such actions. I guess Hurricane Katrina may (and will hopefully) change this alarming trend.

  164. Keith Moulton:

    The level of discussion on this board is terrific, and it is striking how many arguments here can be seen as a world view clash between branches of science, as opposed to disagreements between scientists within a field. The PDI as proxy for “destructiveness” (re #73, etc.) is a perfect example. From a climatologist’s point of view, PDI is about the most objective measure of a storm’s overall strength one could possibly devise, yet the same number lacks any meaning to an economist who’s looking at the financial cost. Many will argue that more powerful storms tend to cause more economic damage, which is intuitively correct, but not really accurate… For if GW is real, the amount of human development on land has a causal connection to the physical power of the hurricane. Looking at Katrina, I would suppose the largest chunk of economic loss is the destruction of homes, yet much of that property value can probably be traced to the US housing boom (see this spooky article) which was in turn fueled primarily by the booming — and polluting — Chinese economy. It is for this kind of interdisciplinary conundrum that all sides must find a common language of values and terms to reach consensus.

    Along those lines, I would propose unnecessary loss of human life is the most important measure, yet such a metric does not appear to be posited in the 163+ comments above! That sentiment notwithstanding, I question the implicit assertion in #6 above (re 30,000 deaths in Europe) that rapid climate shifts do not regularly occur without humans involved. My limited understanding is ice cores show rapid changes (ie. several degrees in a few decades) have occured fairly often in the recent geologic past. Objectively, for GW to be really considered a menace, one would want to show it could cause a series of rapid climate shifts which seems doubtful (because if it’s only one shift, then a future cold shift could be avoided for ‘free’).

  165. wayne davidson:

    Re #162 Models, such as GRIB, lack resolution, they can’t interpolate and determine perfect 3D weather between distant fixed points, for instance an inversion between two Upper Air stations, some inversions even 30 miles away. I have measured a warming trend by analysing atmospheric refraction of the sun, at two distinct climatic locations, 2000 miles apart, and found the sun disk getting bigger every year at both locations, sun disks were especially bigger this year. A warmer atmosphere will do that. As shown above, hurricanes get stronger with warmer SST’s, and they merely reflect the state of heat over the region
    they pass over. 2005 being very warm year, almost the, or the warmest in Northern Hemisphere met. history, should not be a surprise for those looking back the last 10 years worldwide warmer climate. Whenever the models will get higher resolution, they may calculate or catch up what we are measuring every day, mean time we can clearly see (6 billion of us) that we are responsible for this warming, and that it is likely going faster, in direct proportionality with humanities world wide economic output driven by growth, and sadly of course its by-product, pollution.

  166. Stephen Berg:

    “Global warming ‘past the point of no return'”:

  167. Mr. Inge B Johannessen:


    It just came to my attention that a “re-search” of Kerry Emanuel’s intensity index (wind speed cubed) by both Kerry Emanuel and James O’Brien (FSU) reveals no significant linear trends (as argued in Kerry’s Nature paper) if one extends the data set backwards to circa mid-1800’s. Kerry justified his choice of not looking further back than 1935 on increasing uncertainty with respect to inferring wind speeds (if I remember correctly). But they seem to have been able to backtrack in time, and these new results contradict Kerry’s Nature findings. To my knowledge Kerry himself ackowledges these new findings. Another interesting analyses concerning monthly SST anomalies in the tropical Atlantic extracted from reanalysis data from the Hadley Climate Model show a slight negative SST anomaly trend (-0.01 to -0.06 C) (mean average 1950-2004).

    I would expect, if these findings are truly legitimate/accurate, that they must eventually be published in the not too distant future.

    -inge (meteorologist, Norway)

  168. Richard Wesley:

    Re: #167

    I just reran the analysis I did in #122 for the full data set. The windspeed corrections are the same as given by Emanuel for other pre-1970 measurements, so one thing that might change the results would be a different windspeed correction for pre-1950 values. If anyone has any insights on how to do a rough correction, please let me know.

    I was unable to find any references to this “re-search” on Google news or on the web and Dr. Kerry’s FAQ for the paper on his web site at MIT makes no mention of this. Can you provide any links? Do you know which findings were being contradicted?

  169. Steve Bloom:

    Re #162: I get the impression that the research in this field is moving very quickly indeed. This from the interview with Emanuel posted on the AAAS site:

    “There is some recent compelling evidence of causality from another source, though. Experiments with climate models at the NOAA Geophysical Fluid Dynamics Laboratory and in Tokyo using the Earth Simulator model have found that with a doubling of CO2, there was an increase in intensity of hurricanes and, simultaneously, an overall decrease in frequency. These results are very much in accord with our findings.”

    Re #168: I don’t know much about this, but is there some reason to think Emanuel’s correction isn’t right?

    On the other subject, I’m not surprised your search came up empty. There are certain parts of the net where there’s a lot of what some might call “wingnut spam” relating to climate. I’ve seen examples of it similar to that mentioned in #167 that were clearly made up from whole cloth. As I recall, there’s someone (else) in Norway who generates quite a bit of it. Don’t hold your breath waiting for a substantive response, BTW.

    As for the claim itself, I think the business about no “linear trend” from 1850 to 1935 is not even wrong. The lack of such a trend would say very little about the 1970-2005 rise unless it showed some kind of long-period oscillation of the sort Gray seems to wish was there, but evidence of such a cycle would be big scientific news indeed (perhaps as big as any implied direct refutation of Emanuel). And yet our new correpondent refers to no such thing. Norway… trolls… hmm.

    I suppose a third possibility is that there’s a consistentish trend claimed from 1850 to 1970, followed by that big rise, making for a graph kind of like … Kerry, meet Mike. :)

  170. wayne davidson:

    Re #166,

    Presently Barrow Strait has no visible great pack ice , very unusual. It seems that Dr Wadhams may be right, positive forcing may not be well factored in the models and that GW is too conservatively predicted. I think very much in terms of symmetry between distant regions. Lack of Arctic Ocean ice ultimately gave Katrina’s warmer Gulf of Mexico SST’s, worldwide heat has reached a new balance .as it does every day. Simultaneous warming at all distant regions on Earth is clearer then ever, the science is understood, but may be not the rate .

  171. Mr. Inge B Johannessen:

    [some inflammatory remarks have been deleted -moderator].

    Re #168: Regarding my first post, the source is originally from Dr. James J. O’Brien, Director of the Center for Ocean-Atmospheric Prediction Studies at Florida State University ( I myself received this “tip” from NASA Goddard/Norwegian Space Centre (Dr. Paal Brekke).

    Mr. O’Brien’s results are presumably so “fresh” that any “googling” wouldn’t highlight any “hits”. Mr. O’Brien claims he’s discussed his results with Mr. Emanuel. He also claims his results show that the recent surge in intensity is well within observed natural variability if one extends the data set backwards to 1850, as opposed to a cuttoff in 1935.

    Note that I also wrote in my original post that if these results are truly genuine, then I would expect them to appear in the peer reviewed litterature sooner than later. If not, well then it certainly won’t warrent any further attention until someone does publish contrary results.

    I would suspect that working with such a short data set (1935-2005) is a challenge with respect to “proving” the existence of statistically significant trends beyond observed natural variability..?

    But from purely physical reasoning, I myself also find it hard not to expect that a warmer climate should raise the theoretical limit of maximum hurricane intensity if all environmental factors (sst, upwelling, shear, lifetime, etc.) coincide in time and space to produce optimal conditions for development and maintenance (which Kerry Emanuel has argued in previous research).

  172. Steve Bloom:

    Re #168 again: Possibly you were referring to tbe discussion on Emanuel’s FAQ page that subsequent to submission of his paper he talked to Chris Landsea about this wind speed issue, made an adjustment and re-did his calculations. Apparently this did not shift any conclusions, though. Maybe you should just email him and ask for the information you want.

  173. Steve Bloom:

    Re #171: Your first post (#167) said new work “by both Kerry Emanuel and James O’Brien (FSU) reveals no significant linear trends (as argued in Kerry’s Nature paper) if one extends the data set backwards to circa mid-1800’s. (…) But they seem to have been able to backtrack in time, and these new results contradict Kerry’s Nature findings. To my knowledge Kerry himself ackowledges these new findings.” This was an amazing and provocative claim for which no sources were listed.

    Your second post (#171) says instead: “Mr. O’Brien claims he’s discussed his results with Mr. Emanuel. He also claims his results show that the recent surge in intensity is well within observed natural variability if one extends the data set backwards to 1850, as opposed to a cuttoff in 1935.” This is way, way different. It no longer claims collaboration between O’Brien and Emanuel or agreement by Emanuel with any such new results.

    The fact that O’Brien has this point of view is not news. He is, after all, rather active in sceptic circles; see, e.g., . Interestingly, this related Washington Post story from just a couple of days ago quotes O’Brien but makes no reference to this supposed new research: . There is no reference to any such recent revelation on O’Brien’s own site: . Emanuel’s site and other MIT sites (e.g., which includes a link to a radio statment from last Monday) also have nothing on it. None of these sources would involve any search lag. All that I can find from O’Brien on the web are repeated claims that a linkage of the historic hurricane record going back to 1850 shows a recurring cycle, and that this explains everything. Emanuel, Webster and his co-authors, their peer reviewers, Nature and the AAAS (publishers of Science) were all aware of this view held by O’Brien and Bill Gray (among others, although Chris Landsea seems to have gotten a little quieter post-Webster), yet the results of neither paper were affected. I look forward to seeing a peer-reviewed paper demonstrating that all of this work is in error.

    The Dr. Brekke you quote is apparently a sceptic of the discredited (my opinion) solar school (see e.g. and ), although perhaps his views have changed since my web search found nothing on this more recent than 2002.

    So, at this point there doesn’t appear to be a lot of content here. I apologize for perhaps over-reacting, but it seems fairly clear that you posted a sceptic-generated rumor and clothed it as fact. Please be more careful. (And BTW I take my own advice; it took me over two hours to review all of the material I cited above.)

  174. Steve Mauget:

    Hmmm.. In the Jim O’ Brien interview is the link cited in # 173 .

    He states:

    “But what’s amazing is if you actually looked at the trends in the Atlantic Ocean – the region where hurricanes form from five north to 20 north – from Africa over to the United States, it’s actually cooling down. So, I mean yes, there are hotspots in the globe which are warming up, but not in the Atlantic hurricane formation region. So, their theory doesn’t really hold water.”

    But when I look at the single figure in Kevin Trenberth’s recent Science paper (“Uncertainty in Hurricanes and Global Warming”, vol 308, 1753-54) the mean SSTA averaged over the tropical Atlantic (“10 N to 20 N excluding the Caribbean west of 80 W”) sure doesn’t indicate recent cooling. Seems unlikely that the slight difference in O’ Brien’s (5 N to 20 N) vs. Trenberth’s ( 10 N to 20 N) averaging region could account for this. Gee whiz, I’m confused…

    [Response: The difference is the time period involved. O’Brien is using data from 1950 to 2003 over which time the mean over the area has barely warmed (and some parts have indeed cooled). However, over the last 30 years there has been significant warming, and over the longer term (say 1900) there has been warming as well. The upshot is that there is cyclic activity in the Atlantic basin, but not over the whole of the tropics – and this is what is significant about the Webster et al results. – gavin]

    [Response: O’Brien seems to have relied purely on the linear trends over the period, which is not well suited to the task if the upturn, as Emanuel notes, is only in the most recent decade. Perhaps more of an issue, O’Brien placed as much emphasis on winter trends as summer or fall trends. One can rightfully question whether cooling trends in winter are relevant to this debate. Emanuel focused only on the part of the year (early Fall) corresponding to peak formation of Hurricanes, which would appear more appropriate. -mike]

  175. PHEaston:

    The Independent newspaper article linked in Comment 166 misrepresents the views of the US National Ice and Snow Data Centre (NISDC). The article imples that ‘the scientists’ believe all Arctic ice melt is caused by man-made global warming. What the NISDC actually says is”

    “Fossil fuel consumption and the resulting increase in global temperatures could explain sea ice decline, but the actual cause might be more complicated. The Arctic Oscillation (AO) is a seesaw pattern of alternating atmospheric pressure at polar and mid-latitudes. The positive phase produces a strong polar vortex, with the mid-latitude jet stream shifted northward. The negative phase produces the opposite conditions. From the 1950s to the 1980s, the AO flipped between positive and negative phases, but it entered a strong positive pattern between 1989 and 1995. This flushed older, thicker ice out of the Arctic, leaving the region with younger, thinner ice that was more prone to summer melting. So sea ice decline may result from natural variability in the AO. Growing evidence suggests, however, that greenhouse warming favors the AO’s positive mode, meaning recent sea ice decline results from a combination of natural variability and global warming.” (

    Thus, the scientists believe man-made global warming is a component, not necessarily the most important, and not a proven one. An analogy is in those who seem to claim that the destruction of New Orleans was ’caused’ by global warming, even if you accept that it was a significant component of the hurricane’s severity. Such over-claiming and over dramatisation of the impacts of global warming does not represent the scientific consensus (eg. as represented by IPCC), and devalues the quality of the scientific debate.

  176. Wayne Davidson:

    “Nothing unusual-ists” always fail to look at the whole planet, always selecting a region in favour of their premise, and then they pounce on that single area forcing the view that the rest of our planet is likewise the same, they should be regarded as climate isolationists, basically thinking that one region has absolutely nothing to do with others. Of course, everything is linked, and there is no way to consider even ponder an active Hurricane season when the Northern Hemisphere climate is cooler.

  177. John D:

    Do you believe that proper levee and protection policies against a hurricane of Katrina’s strength was/is even possible? And if it was possible to protect against Katrina’s severity, to what extent would it have made a difference?

    [Response: Unfortunately this is way outside of our competence -gavin]

  178. wayne davidson:

    RE #175,

    What happened in the Arctic, was a slow, very slow and gradual decrease in cooling, caused by progressively longer warmer seasons, with a feedback loop of warm air reducing albedo, with reduced albedo increasing warm air. Arctic daily sun positions now is the same as the end of March, yet today’s (Resolute) temperature -2 C does not compare with end of March -35 C, albedo plays a role in this especially with all that missing ice and clouds. Familiar Arctic climate cycles are by no means comparable to what we are experiencing here now, with much more warmer weather encroaching almost unabated since 1998. So the referred to Arctic Oscillation has no semblance to anything in human memory here. It is plainly getting warmer in an unprecedented way. With this Polar region warmer, so is your region where-ever it is down South. This is where the debate is, a failure to link one region’s climate with another ultimately leads to a poor understanding of climate anywhere. All these oscillations, ENSO, AO and AMO’s are influenced way beyond their recognized borders. Not recognizing so yields nothing useful.

  179. Stephen Berg:

    There’s an excellent column by James Risbey, Karl Braganza, and Thomas Homer-Dixon in today’s (Sept 19) Globe & Mail from here in Canada.

    The article is available online only to those with subscriptions, but some university libraries may have access to this newspaper.

    I’d highly recommend the article.

  180. Michael Jankowski:

    Re#177, as a civil engineer who often deals with drainage issues and storm events and who has “always known” something like this was going to happen to New Orleans, I would say “theoretically yes, but realistically, probably no” to question #1.

    From what I understand, the levees were designed to withstand a Cat 3 without breaching. However, they were supposed to over-top under the storm surge in a stronger storm, and the most common explanations I have seen given for the levee breaches is that the over-topping wore down the surface soil and foundation on the inner face (the side which faces New Orleans), which led to the structural failures. So even a Cat 3 hurricane may have created the same failure results (I think there has been levee over-topping in New Orleans from lesser hurricanes which hit farther away, so I’m not sure how well it could really handle a Cat 3 or lesser storm with Katrina’s path in the first place).

    Some people are under the impression the levee system in New Orleans was constructed and is improved on time-to-time, like a typical building. This is far from the case. The levee system is a hodge-podge of construction that settles faster than the rest of New Orleans and constantly needs to be built-up and re-inforced. In a lot of ways, the levee system is no “better” than it was 30-40 yrs ago. Construction methods may be better these days, but the regular levee work is/was basically a maintenance effort and not much of an improvement effort. I believe I heard on one of the post-Katrina stories on the History Channel that parts of the levee have settled as much as 4 feet in a year. The discussion on that show of the future of New Orleans included: (1) a huge series of sea walls similar to what the Netherlands has; (2) restoration of the wetlands outside of New Orleans; (3) levees within the levee system so that if one levee fails, only part of the city is flooded; (4) taller levees; and (5) return of some of the city back to its original swamp state.

    With #1-4 in place, the flooding effects of Katrina would likely have been diminished significantly. However, only items #2-4 had really been seriously considered prior to Katrina, and they were part of a plan of construction through 2050 – far too late to do anything. #5 will be VERY unlikely because of politics, but it seems to be a frequent suggestion of many engineers (including myself). #3 will also be politically difficult, but I think it could happen. #1 will be an immense engineering and construction undertaking that could take decades – arguably among the biggest ever in the US.

    So even if the US and New Orleans got serious about these items 20-30 yrs ago, it’s uncertain exactly how much would actually have been in place for Katrina.

  181. Stephen Berg:

    Al Gore weighs in on the climate change-Katrina link:

  182. Steve Bloom:

    Re #179: On growing greenhouse petunias in Nunavut? :) Seriously, when posting something like this please paste in the first paragraph or two and a link (not a copyright problem, BTW), or at least some kind of summary, and maybe something about the authors if you think they’re especially worth listening to; otherwise, I think it’s pretty certain that nobody’s going to follow up, however useful the article may be.

    Re #180: I wonder if #2 (wetlands restoration) will really be possible of the Mississippi is left in its present unnatural course. Also, my understanding is that it was not the levees themselves that failed, but rather flood walls (essentially large reinforced concrete fences set in the middle of levees). They were supposedly designed to withstand foundation overtopping, but whether it was that or direct failure may never be known since the evidence largely washed away.

  183. Lynn Vincentnathan:

    RE #175, and AGW being only one small component (if at all) of vanishing arctic ice and hurricanes. Did you ever hear about the straw that broke the camel’s back?

    While scientists in a detached fashion equally investigate all components, it’s mainly those small human-caused components that I’m concerned with. Afterall, there’s not much I can do about purely natural processes. Not much I can do by myself either regarding GHGs, even though we’ve lowered ours 75%+ from our 1990 (when we started) emissions. But I’m doing what I can, even if insignificant in the larger scheme of things. I’m hoping beyond hope that by removing one tiny straw I might be able to save at least a baby camel’s back, or ease its pain.

  184. Lynn Vincentnathan:

    RE #166 (arctic melting) & hurricanes, I have no idea on the science, but if the arctic ice melts a lot more, would the Northern Pacific ocean warm more (say, during the summer, when they have midnight sun), and could this lead to hurricanes or typhoons possibly hitting LA or San Francisco?

    I read somewhere that even if hurricanes intensify with AGW, they will be pretty much in the same tropical/subtropical areas as today. But I wonder…

  185. Richard Wesley:

    Re: #171

    I hope that my post was not the cause of the “inflammatory remarks”. I was posting late on a Friday afternoon and I apologise if my phrasing was off.

    [the inflammatory remarks were related to another post, not yours. -moderator].

    Re: #172

    Thanks. I did note several corrections listed there, although I have not had time to adjust my model yet. Hopefully some time in the next few days, especially if I can get Landsea’s coefficient.

    My question was more whether the poster in #167 had the pre-1950 corrections that must have been used. As it now appears that there is no there there, the question is probably irrelevant now.

  186. Hank Roberts:

    Re the loop current (147, 156), with the reminder that I’m not a climatologist, just an avid reader — this
    Center for Turbulence Research
    Nonlinear Gulf Stream Interaction with the western boundary current: observations and a numerical simulation

    Fascinating description; color maps; far more that possible to quote about what the “loop current” is and where Atlantic temperature variations are moving around.

    And note their Section 4 — contemplating what happens if deep warm water currents change in a way that changes the current temperature in areas where methane hydrates are in equilibrium, suggesting the possibility of a rapid large scale release of methane gas.

    Quietly nightmarish, to this reader. I don’t know of other discussion in the literature looking specifically at changes in warm currents in relation to known methane hydrate deposits. But this paper has plenty of footnotes to pursue the thought.

  187. Stephen Berg:

    Here’s the link to the G&M article from #179:

  188. Gerald Machnee:

    Katrina has generated a lot of discussion. However the greatest death toll was from a typhoon that hit Bangladesh in November, 1970 killing 200,000 to 500,000 people.

  189. Stephen Berg:

    Re: #188,

    That may be true. However, infrastructure in Bangladesh is terrible, while in the developed world, it tends to be fairly solid. Also, the population density of Bangladesh is very high, while less so in the developed world, so a greater number of people were in grave danger of dying or being left homeless (at the very least).

    Post #188 does not effectively rebut the premise that climate change is happening and that events such as Katrina (and its significant intensity) are at least a partial result of climate change. A couple of years before Hurricane Andrew struck Florida and the Gulf Coast in 1992, a typhoon struck Bangladesh resulting in the death of approximately 140,000 people. (I think this Bangladesh storm struck in 1989.)

    The fact that two very intense tropical cyclones occurred so soon after each other may mean that more frequent TCs will occur and to a higher intensity as a result of climate change, which may result in even more devastating effects. As a previous (and very recent) study has found, Category 4 and 5 storms may be on the rise, and climate change could very likely be the reason for this increase.

  190. Michael Jankowski:

    Re#182: For all intents and purposes, the wall is part of the levee system. The reason for failure is probably pure conjecture at this point. There are other possible natural explanations for the failure, such as creating a slurry and pushing-out earth below the wall and weakening the support that way, construction flaws in the walls, design flaws, material flaws, debris strikes that damaged the wall, etc. There have been other explanations ranging from loose barges striking the levee to the intentional use of explosives.

    As far as wetlands go, there has been talk of re-routing the path ships take south of New Orleans, constructing silt diversion channels, augmentation by dumping sand from other locations, etc.

  191. Gerald Machnee:

    Re evacuations – When Typhoon Talim hit China on September 1, 2005, they were able to evacuate about a half million people, with only a hundred or so dying.

  192. PHEaston:

    In reply to Steven Berg (189): the observation of two strong storms occuring 3 yrs apart on different continents does not on its own make any case that climate change is a contributary factor to either frequency or intensity when compared to conclusions of the IPCC TAR (published several yearas after these events and therefore very unlikely to have missed them) – stating:

    “There is no compelling evidence to indicate that the characteristics of tropical and extratropical storms have changed… Owing to incomplete data and limited and conflicting analyses, it is uncertain as to whether there have been any long-term and large-scale increases in the intensity and frequency of extra-tropical cyclones in the Northern Hemisphere. Regional increases have been identified in the North Pacific, parts of North America, and Europe over the past several decades. In the Southern Hemisphere, fewer analyses have been completed, but they suggest a decrease in extra-tropical cyclone activity since the 1970s.”

    The paper at the start of this discussion is of clear scientific value, representing a progression of work since the TAR, but it appears naive to suggest that every extreme whether event is significantly influcenced by climate change.

  193. Eli Rabett:

    To draw in a legal distinction again, the discussion appears to be between guilty and innocent, while the evidence points to not proven. Given this what is a policy maker to do? I submit that nothing is a very bad choice given the likely outcomes even if there is no casual link. However, I would go much farther than what Roger Pielke advocates because the possibility of a casual relationship between storm frequency and anthropic climate change has not been falsified, and the possibility of stronger tropical cyclones appears to have increasing evidence in its favor. Given the catastrophic consequences of even one Cat 5 storm making landfall in a populated area, strong actions beyond those necessary if there were no possible relationship are called for.

  194. Gerald Machnee:

    Re 193 – We will never be able to stop a hurricane or earthquake, no matter what its strength is. The most significant things we can do is be prepared personally and with respect to government agencies. That means supplies, funds, communication, tents, transportation to be available with less than 24 hours notice. On a longer time period, we must also be prepared for droughts, wet spells, cold and warm spells.

  195. Hank Roberts:

  196. Lynn Vincentnathan:

    RE #193 my legal understanding (as a layperson) would be that we cannot make a criminal case re the link between CC & hurricane intensity of a specific hurricane, which requires “beyond a resonable doubt” (sort of like a scientific standard of p<.05), but there could be a civil case, which requires a “preponderance of evidence.” When I did jury duty the judge instructed it meant “more likely than not” or above 50%. It seems we may be at or above that level of certainty on this. Then re a “precautionary approach,” which might be above 20% or even 10% certainty (depending on the severity of the possible harm), we’ve got all the proof we need.

  197. wayne davidson:


    I think naive would be to postulate that Arctic Air can’t influence the Gulf of Mexico climate. Perhaps those crop destructive extremely cold Arctic airmass blasts destroying oranges in Florida come from the State of Minnessota?

    The reverse influence is true as well. In the Arctic we benifit from warm air advection every day of the year. There is a continuous exchange of heat going back and forth from North to South, South to North. A heat balance is achieved continuously everywhere else on Earth as well. The case for climate change is made when the average temperature of the world increases or decreases. Recent world wide records indicate a steady increase, pretty much found in all regions, which portends something good for Hurricanes, beasts born from heat. Looking back with hurricane statistics will not be comparable to present day history, since we are breaking new temperature increase records almost every year, unfamiliar climates are breaking loose. For those seeking certainty, we know a few of them: The only thing certain is hurricanes weaken or die over land and or colder water. With equal certainty, a warmer planet will lead to hurricanes/typhoons range widening with some having greater intensity, this in itself gives cause to ponder, should we do something to reduce the number of coming storms? Or just compile statistics?

    By the way, 1997 proved to be a very interesting year, with a very large and cold Arctic Vortex in the spring (coldest in memory……… care for an Arctic Oscillation anyone?) , there were very few Hurricanes for the entire same year: 5.

  198. Joe Comstock:

    I have a few questions on your article. Please don’t read between the lines, I’m not laying a trap and have no other motive than learning.

    One, you base much of this discussion on data from past storms, for instance comparing PDI over the last few decades, etc. It seems to me that we can now measure a storm more accurately and continuously than, say, 1900. The Galveston Hurricane of 1900 is measured as a Cat 4, at landfall. Is there any way to account for its strength before landfall, say if it fell from a Cat 5 to 4 just before landfall? Or, more broadly, when does information become as sophisticated as it is today?

    Second, does the PDI measure a storm at landfall, at its peak, or using some average? What I’m getting at, I’m sure you’ve figured out, is whether the PDI’s trend could have anything to do with how accurately we measure storms now, as opposed to in previous periods? Are models used, or direct measurements? At what period does the PDI determination on actual data become perfectly consistent with modern measurements? Again, I’m not laying a poorly disguised trap, I’m trying to learn.

    Third, you describe the AMO as a decades based cycle. What about a centuries-long cycle? I’ve studied history, and I’ve seen that the world undergoes centuries-long warming and cooling cycles which affect argriculture, settlement patterns, glaciers, even wars and the fates of empires. Do hurricane researchers have any models, or direct methods, to measure how active a season may have been in, oh, say 1705, based on possible long duration climactic trends?

    I’m interested in how a long duration model of hurricane activity could show increases and decreases in hurricane strength, frequency and size, which could give a more clear image of how much GW is calling the shots, so to speak. I’m also curious about evidence, and how accurate hurricane measurements are now compare to 1950, or 1920, etc.: it’s the history student in me.

  199. Mark Bahner:

    Hi Joe,

    I’m not an expert on these matters, but here would be my answers to your questions:

    1) “Or, more broadly, when does information become as sophisticated as it is today?”

    We’ve only had satellite data since the late 1960s-early 1970s. Before that, back to approximately the end of WWII, the U.S. had airplanes doing measurements for North Atlantic hurricanes.

    I found this website that talks about measurements at sea that extend back to 1851 for the North Atlantic hurricane basin:

    But I don’t understand how *sea-based* measurements could exist back to 1851, because I can’t believe anyone could or would sail a ship into the eye of a hurricane, to measure the point of lowest pressure:

    2) “Second, does the PDI measure a storm at landfall, at its peak, or using some average?”

    Stefan Rahmstorf explains the PDI as, “Concerning the power dissipation index: this is the wind speed cubed, integrated over the surface area covered by the hurricane and over time.”

    So it’s the wind speed *cubed*, integrated over the surface area covered by the hurricane (i.e., for a given wind speed, a larger surface area produces a larger PDI), integrated over the life of the storm. So it’s not just at landfall, and it’s not a peak. It covers the entire lifetime of the storm, over the entire area covered by the storm.

    3) “What I’m getting at, I’m sure you’ve figured out, is whether the PDI’s trend could have anything to do with how accurately we measure storms now, as opposed to in previous periods?”

    Well, the PDI trend shown in Figure 2 only goes back to 1945…the start of the airplane-monitoring period. So the trend in PDIs only includes two “periods” (monitoring by planes, and monitoring by satellites). Further, there was no real “jump” up or down in PDI in the period of the early 1970s when satellites started to be used. So I don’t think the trend in PDI is significantly affected by planes-vs-satellites as PDI measurement methods.

  200. Mina Jackson:

    Hi, I was wondering if based on the global warming situation and the way that the hurricanes have gotten worse and more frequent over the last 30 years, is it realistic to expect a possible category 6 or 7 in the near future? And what would that mean for the US. Could we ever be ready for such a storm of that magnitude? Thankyou

  201. Steve Bloom:

    Re #200: The short answer is that the people who came up with that scale didn’t define anything beyond a Cat 5 (which is open-ended). On the other hand, Saffir and Simpson failed to copyright their system, so I say it’s fair game. I don’t recall the exact numbers, but if one simply extends the system the largest two or three Cat 5s on record (of which Rita is now one) verge on a Cat 6. As I write this Rita is about to pass over the loop current, and has a chance of becoming the most powerful hurricane on record and, maybe, just barely a nominal Cat 6. I have no idea whether we can expect hurricanes stronger than this strong 5/weak 6 level even under a severe global warming scenario; perhaps Stefan can address that. A Cat 7 would be unimaginably powerful, with sustained winds well over 200 mph (which begins to get into tornado wind speeds); hopefully we don’t have to worry about any of those.

    As Roger Pielke, Jr. never tires of saying, by excessively developing the Gulf and southern Atlantic coasts we have already put ourselves in a position where we can’t handle large hurricanes. It’s the type and extent of such development that will have to change, and I suspect it will take more than Katrina plus a worst-case Rita scenario to change that. Maybe if we start getting two or three such hurricanes each year for several years running that would do the job.

    Re #198: Just to add a little to Mark’s comments, for the reasons he mentions (and others along the same lines) both Emanuel and Webster et al couldn’t consider anything earlier than the modern period of accurate measurments. Both have been criticized for this decision, and various claims have been made that there’s a big spike in actvity somewhere between 1850 and 1950 that gives the lie to their work (by proving the existence of natural variability capable of producing the sort of hurricane activity we’re now seeing). So far, none of these critics have come up with a reasonable analysis to back up their claim.

  202. Chris Reed:

    Thanks for the comments everyone, this has been very informative. What I have to say here veers somewhat from scientific method and rigor. So shoot me down at your pleasure. ;) With regards the legal analogy drawn in by Lynn and Eli, ‘beyond reasonable doubt’ is used in criminal law here in the UK. But we also have ‘on the balance of probabilities’ in civil law.

    From my understanding whilst not ‘scientifically’ attributable. I consider that in an everyday sense the destructive power (as opposed to effect which is affected by locations) of Katrina (and potentially Rita?) can reasonably be attributed to climate change (i.e. on the balance of probabilities). For example smoking increases the risk of cancer, but you can’t guarantee every smoker with lung cancer got it from smoking. However against a back-ground of smoking it’s reasonable to associate the smoking habit with a smoker’s cancer.

    Likewise, from what I have been reading there is now considerable evidence of climate change (indeed it may well be accelerating?). So I think that to dismiss attribution is unreasonable. As in the smoking issue we have a factor (climate change) that reasonably causes a pre-disposition to a risk (of hurricanes).

    I accept that this does not guarantee that we’ll have Hurricane’s like this every year. And I accept that other oscillatory climate signatures may play a part. Emanuel shows an increase in potential destructive index since the 1980s/90s. And the SST/Hurricane intensity link seems observationally and theoretically grounded. So in view of the other effects of climate change globally, I’m expecting such Hurricanes to become a regular fact of life for those who live in the Gulf Coast states.

    Best of luck Texas, I hope Rita spares you.

  203. wayne davidson:

    I get to understand why Global Warming is not seriously discussed amongst the populace in general, by watching many TV Meteorologists, who utterly confuse the matter, who also seem to be limited by the range of their Doppler radars, seldom explain anything more than the latest extreme Hurricane activity as the result of a “cycle” . Even one , based from NY, on Larry King last night claiming something like “we don’t know much about these (hurricane) cycles”. A declaration of ignorance, if I ever heard one. Of all the scientists I’ve recently seen on TV , not one dares to explain our much greater understanding in basic Global meteorology , as if they are under a meteorological inquisition, banning them from explaining that the Earth is not the center of the Universe. Its time that TV producers, capable of covering the mysery caused by Katrina, bring out at least one Global Climate/Meteorologist expert not fearing the inquest.

  204. Michael Jankowski:

    Meteorologists are generally busy dealing with and focusing on “weather,” not “climate.”

    The populace in general rarely seems to understand the formation of a thunderstorm when a meteorologist explains it. I recall the massive el Nino confusion when meteorologists often tried to briefly and simply explain it in the late 90s. El Nino simply became the butt of jokes on Leno and Letterman.

    I think you vastly underestimate the complexity of hurricanes and climate in general. Remember, Katrina was a “minimal Category 1” in southern FL and wasn’t supposed to strengthen much at all while turning up to hit the FL panhandle. The eye was only 10 miles wide with hurricane force winds only 15 miles from the center. The path it took instead is what determined its intensity and level destruction.

  205. Lynn Vincentnathan:

    I’ll ask this again and hope someone responds. In a GW world, with Artic ice melted a lot during the summer (see #166), could hurricanes get farther north up the California coast, say, to San Francisco. My reasoning it this: the black N. Pacific & Arctic iceless oceans would absorb a lot of heat, especially during summer when there is “midnight sun.” I also sort of understand the physics of a cold glass of water warming rapidly after the ice melts (whereas during the melting tremendous energy was going into the melting process, and now goes directly into the water).

    I don’t know much about currents, wind patterns, etc. So, what is it: Could we possibly, in any stretch of the imagination, get hurricanes as far north as San Francisco, or is this just simply impossible due to other factors?

  206. Lynn Vincentnathan:

    RE #202, my #196 was cut off my mistake. I also brought up our civil law standard “preponderance of evidence” (unlike the criminal standard of “beyond a reasonable doubt,” which might be similar to the scientific standard of 95% confidence). I’m no legal expert, but during jury duty the judge instructed us “preponderance of evidence” meant, “more likely than not.” So it seems to me that rolling a 6 is more likely than not due to it being loaded, and likewise Katrina & Rita are more likely than not enhanced (at least in a small part) by GW.

    Now if we go to the “precautionary standard,” then even 20% or 10% confidence that GW is enhancing these storms is enough “evidence” to start turning off lights not it use or even ponying up $3 to buy a compact fluorescent bulb. Then the savings from those measures can be plowed into more cost-effective, money-saving GHG reduction measures, and we’re then on the right road. Next move, we could buy a house closer to work…..just try to avoid the hurricane, storm, & flood areas….

    RE # 203, follow the money…sponsors, family members (one weatherman is related to…) & other connections.

  207. ba:

    Before the hosannas about “…of the century”, “…of the millennium” start with Rita, I might caution those new to watching the Gulf/Caribbean hurricanes about history, legend and statistics. The killer of record is the Great Hurricane of 1780. Post WWII, the Gulf coast’s offshore structural industry had to redefine “100 year storm” more than once in its first half century. I suspect after this year that it may need to do so again. Some coastal Texas indians seemed to think the Big One was ~1816 (pre Anglo colonial experience, probably not Galveston 1818). Maybe one shipwrecked “white man” survived it. Coastal Texas’ place names echo the ghosts of cities and towns wiped out by hurricanes, this one promises to be awesomely ugly too.

    In this millennium, 2001-2, we have already witnessed the advance of science starkly illuminate our *orders of magnitude* ignorance about ocean motion – “freak waves” that still disappear large ships, sudden structural failures – no SOS. These waves turned out to be shockingly common with 3 weeks data from satellite surveillance.

    Food for thought: 1960-61 was a Cat 5 double, double-header.

  208. Dan Allan:

    I have a question for the serious climatologists:

    As I understand it, the GCMs do not generally forecast an overall increase in number of tropical cyclones, although they do forecast storms of greater intensity. In any case, the predicted correlation between AGW and annual PDI is not, apparently, expected to be that dramatic.

    I struggling to understand why that would be, as hurricanes are particularly sensitive to relatively small changes in SST.

    As I mentioned in an earlier post, hurricanes require SSTs of >= 80f to to form. There are other factors, but this is an absolute prerequisite. In a high-carbon environment, it seems safe to presume that (a) more of the surface area of the oceans would be above 80f, and (b) these areas would remain above 80f for a greater portion of each year.

    All other factors being equal, this would lead one to assume that hurricane frequency should increase exponentially with increasing global SSTs. But that does not seem to be what most modelers predict. So the question is: why not? Perhaps all things are not equal. The most common reasons for hurricanes to “fail” to form in high SST environments are (a) not enough coriolus effect (near the equator – not likely to change any time soon, (b)wind shear, and (c) too dry an atmosphere. So do the models anticipate greater wind shear in a high-C02 atmosphere? Do they anticipate drier atmosphere?

    Comments welcome from anyone.


  209. Steve Bloom:

    Re #205: The cold Humboldt Current that runs along the CA coast is a typhoon-killer, meaning that probably all we have to worry about here is the lack of adequate preparation for the inevitable great earthquakes. Lucky us.

    Re #207: Strengths of these historical hurricanes are hard to pin down, but of course it would be foolish in the extreme to assume that the TX coast hasn’t been hit by Rita-sized storms on numerous occasions in the past. Even the short period of modern records proves that it’s only a matter of time before every single spot on the Gulf Coast is hit by a major hurricane. Unfortunately, the current extent and type of coastal development implies different assumptions.

  210. wayne davidson:


    Yep it is simple. Orphelia went over cooler water for a great deal of time, and it never was a Katrina, or a Rita, Katrina’s deviation made it last longer over warmer SST’s, thus gaining strength. What is not simple is why Meteorologists can’t say GW, especially after a point blank range question is asked, like Larry King’s:: “Is the weather changing?” … Is amazing what they would say instead of dealing with the real answers. Was not New York very warm this summer? Could their be a connection…… I wonder?

    TV Meteorologists are very well spoken, they can express themselves especially in simple terms, it is a not hard to say: “Its warmer all over the world” as it is, June-July and August 2005 was the warmest in history for the Northern Hemisphere, and this gave the warmer SST’s. Have you heard from a TV Meteorologist yet that it was the warmest summer in history? May be they have a GW phobia….

    #203 You may be right about the money, but it costs more in the long run, especially to the thousands of families displaced, with countless lives shattered by the havoc we (polluters) made stronger and more frequent. The Range of Hurricanes/Typhoons will grow, but whether they hit the West coast one day, will depend on dominant winds, which will likely change as well, you need access to a GW model.

  211. Lynn Vincentnathan:

    #207, so what I gain from your piece is that Katrina & Rita are well within “normal” & not as bad as the worst – which means to me as a Rio Grande Valley resident, I have some extraordinarily big, perhaps Cat 6 hurricanes to worry about in the future with GW enhanced hurricane intensity. You’ve scared me now. Previously I was just concerned about GW harms to others.

  212. Michael Jankowski:

    ***What is not simple is why Meteorologists can’t say GW, especially after a point blank range question is asked, like Larry King’s:: “Is the weather changing?”***
    Maybe the answer to that is, “Larry, the weather is always changing. It always has, and it always will.” Maybe they don’t see the link to global warming that you do. Maybe GW is outside the scope of the work that most of them do. Maybe they’re more worried about current and near-future weather conditions (which, obviously, can be quite serious) and leave the GW talk to politicians and climatologists.

    ***Have you heard from a TV Meteorologist yet that it was the warmest summer in history?***
    Once again, TV meteorologists focus on “weather,” not “climate.” I don’t watch a lot of TV weather these days, but back-in-the-day, they seemed to love talking about record highs here-and-there, how wet/dry we were compared to usual, how cold/warm we were, etc.

    I was shocked in early 2001 when I saw a newspaper headline, pretty much buried, stating we just had the coldest two month period in history in the US (set Nov-Dec 2000). The TV meteorologists back then weren’t ranting-and-raving about this historical cold event, either. Should they have spoken-up and linked it to global warming?

  213. Hank Roberts:

    Here’s that ‘Loop Current’ charted

  214. Pat Neuman:

    Re #212 [***What is not simple is why Meteorologists can’t say GW, especially after a point blank range question is asked,] …

    Some don’t want to risk their reputations, carrers or loose their jobs.

    However, some are willing take a chance. The lead meteorologist at WCCO in the Twin Cities demonstrated the seriousness of global warming to lawmakers at the MN state capitol on 21 February 2005. Lawmakers have short memories on global warming. They passed a huge road transportation bill a couple months ago, and were proud of it.

    Summary of Testimony by Paul Douglas and Polar Explorer Will Steger at:

  215. GJ:

    Another problem besides GW is stupidity.
    The national Sierra Club was one of several environmental groups who sued the Army Corps of Engineers to stop a 1996 plan to raise and fortify Mississippi River levees. The Army Corps was planning to upgrade 303 miles of levees along the river in Louisiana, Mississippi, and Arkansas. This was needed, a Corps spokesman told the Baton Rouge, La., newspaper The Advocate, because â??a failure could wreak catastrophic consequences on Louisiana and Mississippi which the states would be decades in overcoming, if they overcame them at all.

  216. wayne davidson:

    re #214,

    Good to know WCCO carrying simple facts, thanks to meteorologist Douglas, unfortunately he seems to be a lonely voice amongst many other peers. Mr Steger does not want other explorers to swim to the North Pole, his contemporary explorers carry in their memories, the cold days, he should come back and report and compare how much Polar Ice conditions have degraded.


    2000 had a cold USA November/December leading to a remarkable 2001 season of only 8 hurricanes, 2nd place for the least number with 1995-2005 stats, 1997 being another cold spring giving only 5 hurricanes. There seems to be a direct causal link between cold winters and the number of hurricanes. 2005 winter and spring was mild and there are at least 18 hurricanes. Spring and summer of 2005 from March to August is #1 warmest in Northern Hemisphere history, this is 6 months of quasy total silence on basic reporting by most TV meteorologists.

  217. Steve Bloom:

    Folks may be interested in a small debate I’m having with RP Sr. over at . He seems to think Pat Michaels’ latest TCS post attacking Webster is legit, whereas my “audit” finds a number of problems. Has RP Sr. lost his objectivity in a rush to defend his fellow State Climatologist?

  218. Jan Theodore Galkowski:

    Something which doesn’t get a lot of play in the global climate change discussion is the warming commitment issue. That is, even if all anthropogenic warming were suddenly stopped now, warming would continue because of the inertia of the oceanic system. This has been described in two articles in SCIENCE, namely,


    Of course, this does not mean suspending activities which contribute to warming is futile. What it does mean is that mitigation of climate change effects should be front center in policy. In my opinion, the most damaging effect of denying there is warming is the failure to mitigate or try.

    Of course, in addition to anthropogenic warming, there may be natural warming for whatever reason, and we may not be able to do anything about that. But whether there is or not and whatever fraction is human-controlled, the effect of both is worse than the effect of one and should be more of a reason to take immediate action, not less of one.

  219. Pat Neuman:

    Douglas wrote a special report for the Minneapolis StarTribune (November 20, 2004) titled:

    “Capricious weather? Get used to it”

    Excerpts follow…

    Paul Douglas, senior meteorologist of the WCCO Weather Team (and author of a book “Restless Skies).”
    … Proving cause and effect is nearly impossible. But evidence is mounting that a warmer climate is sparking more weather extremes, especially over northern latitudes from Alaska to Minnesota to New England. Warmer air holds more moisture, which increases the potential for flooding rains, tornadoes and hail.

    Sen. John McCain, R-Ariz., visited the arctic regions of Iceland and
    Norway late this summer and, according to the New York Times, he was
    disturbed by the rate of warming he witnessed. “The Inuit language
    for 10,000 years has never had a word for robin,” he said. “And now
    there are robins all over their villages.”

    Prof. Mark Seeley, who studies meteorology and climatology at the
    University of Minnesota, said his records show that we have had eight
    consecutive Novembers in Minnesota mild enough to play golf. “This
    trend has been mostly unprecedented, historically,” he said.

    Dan Luna, chief of river forecasting at the National Weather Service
    in Chanhassen, said: “It would be hard-pressed for anyone to argue
    that we’re not seeing evidence of warming. ‘Why?’ is another
    question, but we’re just not getting the really cold winters anymore.”

    … Craig Edwards, chief of the National Weather Service office in Chanhassen, the newest technology is so sensitive that it’s picking up previously unnoticed tornadoes.

    Colorado State University Prof. Roger Pielke, who studies the societal impacts of severe weather, said: “There have always been ups and downs and severe events, but as a nation, we are far more vulnerable than ever before.”

    J. Drake Hamilton, science adviser for ME3 (Minnesotans for an Energy
    Efficient Economy), said she’s concerned about possible shifts in our
    weather patterns and the growing number of severe weather events.
    “Right now, the climate of Minnesota, if we do nothing, will change
    about 100 times faster than it has in the past, getting much warmer,”
    Hamilton said. “Within our lifetime, winters in Minnesota will become
    more like winters in Chicago – warmer with less snow and more
    precipitation coming as rain.”

    … Prof. emeritus H.E. Wright of the University of
    Minnesota’s Department of Geology and Geophysics: “The most striking
    thing about recent trends is the very rapid changes that are taking
    place. These temperature increases are unusual in their intensity and
    the sheer rate of change.”

    BTW, Will Steger and his dogsled team went back into the arctic in 2004. He reported real time via the Internet for schools and others, but there was minimal media coverage in the Twin Cities area.

  220. Joseph O'Sullivan:

    Re #215 (GJ)

    The litigation mentioned did not stop levees that would have protected New Orleans. For an overview of this and useful info on the levee issue some environmental attorneys and legal scholars have given the whole story here

    I think the levee issue touches on some of the points that Rodger Pielke Jr has brought up on the use of science in policy-making. Roger brings up a good point that focusing research can provide answers to policy questions and can be used to make better regulatory decisions. However, just having the science that answers policy questions is no guarantee that policy makers will act on the information. Scientists and engineers having been warning policy makers about New Orleans vulnerability to hurricanes for decades but decision makers chose to do nothing.

  221. Stephen Berg:

    “UK scientist slams U.S. climate ‘loonies'”:

  222. Michael Jankowski:

    Speaking of meteorologists opening their mouths

    Re#215, A curious piece of work. I didn’t get very far. The first time I went through it, I basically stopped near the top of page 2 where Bush is admonished for claiming nobody predicted the levees would breach. The reference provided for “in fact, over a period of many years, scientists had predicted that a strong storm surge could breach the levees” is a Sept 14, 2005 Washington Post article. So I would have to find an article written two weeks after Katrina and hope that it properly reference these “predicitions.” If not, I’d be left following a paper trail going who-knows-how-long. Did the authors simply take the Washington Post article at its word, or did they check the original sources? Why can’t references be done properly?

    FWIW, another LSU modeling effort which suggest that in a Category 5 with the worst-case New Orleans path, the no part of the levee should fail: “”Another scenario is that some part of the levee would fail,” Suhayda said. “It’s not something that’s expected.” . Suhayda himself is also quoted in the “Center for Progressive Reform” piece, so I would assume he’d be considered more than reputable. If the levees weren’t supposed to fail in a worst-case Category 5, why would the levees be expected to fail in a Category 4? Was it possible? Sure. But I think it’s taking Bush’s comment out of context to claim he was saying that it was a 0% chance (and I don’t see the point of including the Bush comments in the first place other than for the purpose of taking shots at him).

    I also don’t buy the argument in the piece that just because the proposed floodgates were only designed to withstand a Category 3 hurricane, they wouldn’t have been of significant benefit. As the piece points-out repeatedly, the levee system itself was only designed to withstand a Category 3 hurricane, yet the vast majority of the levee system did not fail and did offer protection from the storm. And while other factors may have contributed, it sure does appear that the environmental lawsuit was the primary factor in derailing the floodgate project.

    The opposing view is just as convincing and can be found here, for example , which does contain the scientific opinion from an LSU researcher that the floodgates would have been of great benefit.

  223. wayne davidson:

    # 221
    It is very hard to defend contrarians who base their science on maximum confusion rather than clarity, the Independent had a clearer conclusion, they can’t be convinced on anything, but loons are usually smart birds easily persuaded of pending dangers. It is quite stunning that this contrarian view has such a pervasive influence, especially since its devoid of any substance…

    #219 Northerners in General feel GW a whole lot more than anyone else, cold air is usually very memorable, use to be more punctual, loosing cold is a good thing for some, but in the South a nightmare to others. To add to Senator McCain’s Robin story, Killer whales, Orca pods were first seen in the High Arctic a few years ago, an awsome sight to those not use to them.

  224. Joseph O'Sullivan:

    This is off topic so I will reply only once.

    #221 (Jankowski) I think you are confused again, this time about the citing and the courts.

    The authors of the Center Progressive Reform (CPR) are nationally recognized experts in environmental regulation, and as attorneys of this caliber (including Supreme Court victories) they are well known for their thoroughness. One was one of my law school professors. They are not like Michael Crichton and their work is not like State of Fear.

    This issue of the lawsuits stopping levees was started by the CEI in an article that brought up levees that where in no way connected with the destruction or protection of New Orleans and floodgates that were not stopped by environmental litigation. The CPR was started to counter groups like TCS, CEI and Cato’s intentional misrepresentation of environmental regulation.

    The statements about the strength of the levees are taken from the Army Corps Engineers own testimony.

    About the lawsuit stopping the floodgate project, the court said that its opinion and order should “in no way be construed as precluding the Lake Pontchartrain project as proposed or reflecting on its advisability in any manner,” and it stressed that “upon proper compliance with the law with regard to the impact statement, this injunction will be dissolved and any hurricane plan thus properly presented will be allowed to proceed.”

    The Corps had to do the environmental impact assessment, and even if the assessment showed a negative environmental impact this would not have stopped the project.

    Now a politician is using these misrepresentations spread by the CEI and its allies to harass environmental groups and weaken environmental regulation. Yes you guessed, its Senator Inhofe!

  225. PJK:

    #208. I understand the Atlantic hurricanes are born if a) sea surface temp exceeds 27 deg in a rather thick layer; b) there is little wind shear and c) there is a suitable seminal thunderstorm cluster moving westward in the Intertropical Convection Zone (ITCZ) over the equatorial Atlantic.

    Satellite imagery frequently trace these thunderstorms that later turn into hurricanes from as far away as East Africa.

    Now, imagine an advanced monitoring system capable of analyzing these far-away storms in detail, coupled to a near-perfect model covering fully the whole life cycle of a tropical storm that will be transformed into a hurricane. It migt then be possible to do something about the hurricane, perhaps killing a number of them before they harvest enough energy to be a serious threat, or to steer them away to a less dangerous path. A full-blown storm can not be influenced as it would take too much energy, but an early stage, maybe?

    Convective clouds can be artificiially modified to some extent, i.e. to prevent hailstones from forming. Dust from Africa seems to have some similar effects on the early potential tropical storms, as indicated by today’s discussion on the site:

    “Elsewhere in the Atlantic:

    A tropical low near 55 west, south of 21 north was moving westward at 10-15 knots. Showers and thunderstorms are accompanying this wave, and development is not expected for at least the next two days. A tropical wave was along 39 west, south of 20 north, moving west at 10-15 knots. Nearby, African dust continues to limit convection with this system, so no development is expected in the near future.”

    A climate change impact might result if the ITCZ seasonal movement were changed. Western Africa has a long east-west oriented coastline which forms an unlinear factor in the annual regional ITCZ cycle. Number and intensity of the seminal thunder clusters may change as a result. I can not imagine how …

  226. wayne davidson:


    A worldwide re-forestation program may be infinitely more effective way of reducing hurricane numbers, and of course a huge effort in reducing greenhouse gases, like a million wind towers made by US-Steel and GE for example, all placed in ideal locations like on giant sea or lake platforms, mostly producing Hydrogen almost 24 hours a day… The damage is done, but we can at least try to reduce further impacts.

  227. Mark Trexler:

    A major piece on climate change and hurricanes appeared at today. Excerpts are provided below (I’ve intentionally focused on the skeptics). Seems odd that the National Hurricane Center would be so aggressively discounting potential climate-intensity links. Any thoughts?

    (CNN) — Hurricanes aren’t behaving like many of us are used to them behaving. They’re bigger and meaner, and more numerous than many people have seen. But don’t rush to blame it on global warming, experts warn.

    Max Mayfield, director of the National Hurricane Center in Miami: “The increased activity since 1995 is due to natural fluctuations (and) cycles of hurricane activity driven by the Atlantic Ocean itself along with the atmosphere above it and not enhanced substantially by global warming,” he testified.
    Mayfield’s colleague at the National Hurricane Center, meteorologist Chris Landsea, said the impact of global warming is “minimal for the forseeable future.” Landsea said the studies indicate global warming could increase hurricane wind speeds and rainfall by about 5 percent –100 years from now.
    They say the string of major storms that have struck the southeastern United States over the past two seasons signal a return to normal.

    “The only thing I can say,” he added, “is this run of good luck we had is ending.” “This year you can just say nature is averaging out its climatology,” said Colorado State University’s famed hurricane predictor, William Gray. In 1915, Gray said, New Orleans and Houston areas were hit by Category 4 storms six weeks apart. “You can’t blame that on global warming,” he observed.
    And so, to a generation of Americans with little experience with hurricanes, it seems like these monsters are coming out of nowhere.

    Gray and Willoughby are among the skeptics who doubt global warming can be blamed for the trend of the past few years. They are joined by the hurricane trackers at the National Hurricane Center. “You see a few decades of slower activity, followed by a few decades of higher oscillation,” he said. “Our position is the recent increase in hurricane activity is not caused by global warming.”

    Willoughby said he is keeping an open mind about the role of global warming but believes it won’t be a factor for at least another 100 years.

    Gray was more direct. “There are all these medicine men out there who want to capitalize on general ignorance on this subject,” he said. “With all the problems in the world, we shouldn’t be dealing with this.”

  228. Steve Bloom:

    Re #227 (Trexler): Landsea was Gray’s grad student. My impression is that the North Atlantic natural cycle stuff originated largely with them.

  229. Stephen Berg:

    Re: #227, “Seems odd that the National Hurricane Center would be so aggressively discounting potential climate-intensity links. Any thoughts?”

    Easy. If they were saying too aggressively that climate change was the cause of this increased activity, they’d be booted out the door by their employer, the present government.

    Also, in response to this:

    “Gray was more direct. ‘There are all these medicine men out there who want to capitalize on general ignorance on this subject,’ he said. ‘With all the problems in the world, we shouldn’t be dealing with this.'”

    Didn’t the Pentagon (yes, the Pentagon!) say that climate change would be the number one national security (not to mention global security) problem of the 21st century? We must deal with it NOW, before it is too late to do anything to stop or slow the change.

  230. Michael Jankowski:

    “#221 (Jankowski) I think you are confused again, this time about the citing…”

    I agree, I am confused about the citing. In particular, I was speaking to reference 4, which appears on page 2. I was assuming this would point to a number of scientists who’d warned of levee failures “for years.” Instead, I found only a comment from a single scientist, Hassan Mashriqui, dated May 19th, 2005. I see no legitimate justification in the cited reference for the claim of “in fact, over a period of many years, scientists had predicted that a strong storm surge could breach the levees.”

    Now near the end of the Washington Post editorial, it does say, “Woodley cautioned that the investigation of the catastrophe has just begun, but many scientists, environmentalists and St. Bernard Parish officials said they do not need a forensic investigation by the Corps of Engineers to know that their warnings have come true.” However, this statement -at least with regard to “scientists” – is not backed-up elsewhere in the document. These scientists are not named, and there is no citation. Surely this editorial paragraph alone was not used by CPR as the citation for their quote?

    Maybe CPR was simply citing the editorial for the next sentence – its claim of what went wrong in New Orleans – but that would leave the very strong CPR statement, “in fact, over a period of many years, scientists had predicted that a strong storm surge could breach the levees” lacking any supporting evidence whatsoever. So, yes, I am confused.

    This statement basically appears on page 6 in a more open form, not restricted solely to levee breaches: “Scientists had for years prior to the storm predicted the levee system could not withstand a Category 4 or Category 5 storm.” I certainly agree with this, and it was widely know that the levee system was not designed as such. The citation references are collectivley #28, which can be found here and here . After reading through the citation(s), I find no mention of levee breaching – just over-topping and concerns with the height of the levees. And according to every report I’ve read, many, if not all, of the levee issues with Katrina were not caused by over-topping. So while it is true that the levee system was not designed to handle a Cat 4 or Cat 5, this citation does not contain any supporting evidence concerning scientists saying “for years” that Katrina-esque “levee breaches” would happen.

    References #32 and #33 are either parts/all of #28. While the citation does support that these levee locations are weak-points and that the levee system was not designed to handle anything above Category 3, they are stated as a weak-point for over-topping, not breaching. Once again, these citations appear to be taking the source material out of context.

    Of course, I believe Katrina was actually only a Category 3 when it got to New Orleans (although possibly preceded by a Category 4 storm surge to some extent), so I’m not quite sure why there’s so much talk about Category 4 and 5 protection in the first place with regard to Katrina.

    Maybe the CPR folks are outstanding lawyers, but either (A) they don’t know the difference between a levee breach and levee over-topping or (B) they don’t want the readers to be able to differentiate between the two.

  231. Gerald Machnee:

    Re #225 to @229. I do not see where Landsea, Gray, or Mayfield have said anything wrong. They have been studying and dealing with hurricanes more than the commentators and interviewers. They have also studied them back a century or more. Too many people have a big one run at them today and the first thing they exclaim is “Global Warming”. As I said in an earlier post, there was a lull in the 60’s and too many people and businesses built in hurricane prone areas. Hurricanes in the Atlantic do have cycles and this cycle of higher occurrences is not over yet.

  232. wayne davidson:


    This hurricane cycle……. Does it warm up the rest of the planet?

    Science starved, to say the least, articles are coming out about Hurricanes, and that “cycle” they keep on harping about, is a total smokescreen, designed to confuse and hide the obvious cause. Not one meteorologist proposing a negligeable effect from GW has provided a hint about the Northern Hemisphere currently at a all time high in temperatures, none of these articles show anything of the sort. Why would some (GW-phobic) scientist not mention this? Having full knowledge that warmer SST’s are very important for increasing Hurricane intensities would make it a basic requirement in explaining otherwise, something they don’t want to say, that a warmer planet causes more hurricanes. Irregardless of cycles.

    Their logic seems to be: the Hurricane cycle is at its peak. How can they possibly exclude the rest of the world’s weather? Do hurricanes dwell in a closed near equatorial thermal system? Does the Atlantic absorb heat only near the equator? Are no heat transfer processes between Atmosphere and Oceans the new norm?

    Those making such claims have some explaining to do, either they admit that Hurricane cycles are independent of the rest of the world’s climate, or SST’s can’t be cooled or warmed by extra regional influences, either way they will violate basic meteo-hydro-dynamic laws, which makes their stance at the very least dubious.

    Here is one more article precluding NH all time temperature highs while discounting GW (I am sure there are many others):

  233. Bob Holloway:

    In reading your thoughts on global warming and its effect on hurricanes I find an analogy in steroid use in baseball. A hitter would still hit home runs not on steroids but on steroids the home runs he hits are longer and more importantly what would have been long fly balls for outs are now homer runs. Global warming is not a cause for hurricanes but it makes the hurricanes that develop stronger, and more tropicals storms become hurricanes.

  234. PHEaston:

    A balanced article by the BBC. Of particular interest is the graph 2/3 of the way down the page showing ‘Hurricanes striking US mainland each decade’ – from 1851 to 2004. This demonstrates that the long-term historical record, rather than events in a single year, is much more important for understanding what is happening.

  235. Pat Neuman:

    “the chance is 1 in a 1000”

    Katrina, Rita, Hurricanes, Global Warming
    What’s the bottom line?


    As we pointed out previously, the North-Atlantic oscillation might explain the increased hurricane intensity in the Atlantic, but not in the Pacific. Still, the two increases could have been a coincidence. The Webster article piles on four more such coincidences. The final table in that article gives the percent of category 4 and 5 hurricanes in the first and second 15 years of the study, and zFacts has graphed those values below: (spreadsheet for graph and t-test)

    — Graph at link below

    This pattern does not look like coincidence, but just how unusual is it? This can answered with one of the first and most famous statistical test “Students” t-test for paired data, and the answer is that the chance is 1 in a 1000. That’s how unlikely it is that six different ocean basins would have these increases in hurricane intensity at the same time unless there is some common cause. The most obvious explanation is global warming, precisely because it is a global effect.

    – Steven Stoft

  236. Stephen Berg:

    Re: #233: “Global warming is not a cause for hurricanes but it makes the hurricanes that develop stronger, and more tropicals storms become hurricanes.”

    I disagree. My thoughts are that climate change will cause storm intensification, as well as storm formation. With the slowly increasing SSTs as a result of global warming, greater numbers of tropical depressions will likely form, which, over warm water may mature into tropical storms, which over even warmer water may strengthen to tropical cyclones.

    This is to say that 25 C waters which warm to 27 C as a result of climate change (i.e. from below the temperature necessary for TD, TS, and TC formation to above this critical temperature), which is certainly possible (and is currently in the process of happening), will likely result in the formation of such storm systems where, without global warming and the resulting ocean temperature increase, would not have occurred.

  237. Ed Erpelding:

    It appears to me that the ratio between the SST increase and the power of hurricanes (PDI)is by the power of two. (exponentially). That is shown Figure 2.

  238. ba:

    Re #211 You scare yourself. Albeit the Rio Grande has had a few ‘canes, â��Cat 6â�� indeed. If you don’t like the risk, improve the odds – prepare, strengthen your house or move. You do not have a statistical basis to whine that we are out of historical range. If we pick up 3 more Cat 5s (usually a transient intensity in the Gulf) in the next 14 months, we should have a discussion about improved remote data gathering effects on statistics, Cat 3+4+5 statistics, and the 2nd deviation limit (~97%). The PDI, although an interesting presentation graphic, suffers on its historical data coverage & quality and its relatively short time base.

  239. PHEaston:

    Re: Stepehn Berg (No. 236)

    You say “My thoughts are that ….” Science is not based on ‘thoughts’.

    If you have evidence that hurricanes have increased in number and intensity in correspondence to CO2 emiissions, please provide a reference.

    What the IPCC TAR report says (Table 1 of ‘The Scientific Basis’) is:

    “Increase in tropical cyclone peak wind intensities: Not observed in the few analyses available”

    “Increase in tropical cyclone mean and peak precipitation intensities: Insufficient data for assessment”

    Thus, by 2001, there was no evidence for a global warming influcence on hurricanes. If there is new convincing evidence, please let us know (one ‘extreme’ year is not enough). The paper at the head of this dicussion is based on computer modelling, while vluable and informantive, is not evidence.

  240. TCO:

    1. Does the trend go back as far as possible (truncation suspicions)
    2. What is the relation with grid cell temp changes (and yes, I know the overall world has an impact, but the storms are strongly influenced by local sea temp).
    3. What do the curves for other parts of the world look like and how do they behave wrt question 2?
    4. what was the trend during the mid-century-1970s cooling period?

  241. wayne davidson:


    The BBC article “trying to be fair” is almost typical to a US TV meteorologist example , usually BBC armor resists American infuences (BBC should read Canadian media a little more than not), but seems to me it is trying to fall on its sword at times in this particular instance. Bravo, it explained external influences, but alas, like most TV meteorologists it flatly fails to mention that 2005 is a very warm year. Stunning indeed is the decadal graph showing landfall comparisons not including 2005 to date data which would have been more revealing. And that sea temperature graph does seem to indicate a cycle, but alas it fails to connect with Hurricane activity, such as Andrew, born during the coldest SST average in the past 20 years, surely Andrew didn’t gain strength over 27 C seas? Finally I am not sure whether lobby groups on both sides, expressing free or paid will, can beat reality, unless reality is misreported.

  242. Gerald Machnee:

    RE #241 – Do you believe that Andrew gained strength in below 27 C SST? You have now contradicted yourself, as hurricanes require the temperature to develop. In addition they require the correct upper air instability and wind type to develop to category 3,4, or 5. Then Andrew illustrates that certain atmospheric situations are more significant than Global Warming in developing a severe hurricane. Katrina was a near perfect hurricane in having all the required parameters. Have you asked the Hurricane Center in Miami? As an exercise look up all the meteorological data on Andrew. There are many opinions expressed without scientific backing.

  243. Steve Hollingsworth:

    Something new has been noticed this year (partcularly by CNN). The warm Loop Current comes from South America up between the Yucatan and Cuba, then bulges northwestwards into the Gulf of Mexico. Then it exits between Florida and Cuba, and goes up America’s East Coast.

    Hurricanes that track over the Loop current rapidly increase in strength. This happened to Katrina, Rita, Ivan and especially Camille. Then when a hurricane goes off the Loop and over cooler water, it rapidly loses strength – this happened to Rita, which went from a Category 5 to a 3 before landfall.

    The questions then become (1) in this warm year, is the Loop Current warmer than usual? and (2) as waters further north become warmer, are hurricanes tracking further north and thus are more likely to catch the Loop Current?

  244. wayne davidson:


    “surely Andrew didn’t gain strength over 27 C seas?”…. the answer is no of course.. Look at the graph, “titled sea surface temperatures” (where??? what region??? what time span???? ) average SST’s in 1992 were set at about 27.8 C within a certain area???? perhaps averaged for the whole year???? I wrote about this sea temperature graph having no meaning with respect to some severe hurricanes while using Andrew as an example. Graphs in general loose a lot of convincing power when parameters are set too loosely, especially when they are not defined. A more proper graph would be hurricane path average temperatures, a correct direct time and temperature display of hurricane SST’s, instead of a wide generalization, which can be interpreted many ways. The goal of showing this graph was to show a “cycle” which explains this season, area SST’s being in a warming phase of sorts, this graph plainly fails to demonstrate the possibility of an Andrew and likely many other hurricanes, it is poorly defined and not deserving of a BBC article.


    “Based on recent research, the consensus view is that we don’t expect global warming to make a difference to the frequency of hurricanes,” explains Julian Heming, from the UK Meteorological Office.”

    really now?? Is this true?

  245. Gerald Machnee:

    RE# 242-244: If you read the history of Andrew at: you will see how Andrew developed, then weakened and intensified. It indicates the factors involved in development. The BBC site was not specific to Andrew. But the history of Andrew should make it clear that Global Warming was not the significant factor.

  246. wayne davidson:

    # 245,

    What were the sea surface temperatures on Andrew’s path? Does it say that?

    Dr Bill Nye, will be on Larry King tomorrow night, a voice much clearer than mine will address GW vs Hurricanes, suggest all contrarians to listen to the science guy…..

  247. B Johnston:

    I second #243.

    People keep talking about the sea surface temperature being the dominant factor influcing hurricane growth. In this pre-Katrina SST picture, we can see the “warm” loop current as an area of cold water. The growth of Katrina as the passed over the current was explosive. Then, in the post-Katrina SST picture, the loop current and shallow areas are warm.

    What is going on here? I would guess that with the properties changing less with depth, heat can penetrate down easier there, so that it takes more energy to warm the surface, leading to it being cool when the surface is absorbing energy. When a hurricane runs over it and generates large waves, however, the depth of the warm water results in the surface cooling much less.

    Rita did the exact same thing at Katrina, only faster. Both hurricanes rapidly ran up to 170 mph+ wind speeds over water that wasn’t even exceptionally warm at the surface. While a lot of people were able to predict this strengthening based on their forecast tracks, the offical forecasts were not. Andrew’s rapid run up in strength prior to landfall occured over the Florida Straight, farther down this current.

    What these examples clearly show is that it’s not the pre-hurricane SST, but the depth of the warm layer, which is most important in determining the SST during the hurricane and hence the strength of the hurricane.

    I’ve seen precious little acknolwedgement of this critical distinction in this discussion, or in most of the academic discussion. SSTs seem to be taken directly from climate models and plugged directly into hurricane models without averaging by depth to account for the hurricane stirring up the water. Increases in the depth of the warm surface layer seem to be a common result in most climate change models.

    On the global scale, there is no mechanism to counter global warming, so everything indicates that we should expect an increase in major tropical cyclone numbers. In the Atlantic, however, global warming leads to increased precipitation in the North Atlantic and increased iceberg and water runoff from Greenland, both of which decrease deep thermohaline circulation. There is, for instance, an active argument about whether northern Europe will be cooler under global warming, and if so, by how much. Furthermore, we global models also consistently show an increase in el-nino frequency, which is known to cause a major decline at least in major hurricanes making landfall in the U.S., and probably in major Atlantic hurricanes in general. Since we have good reason to expect that the response may be different in the Atlantic, using evidence for increases in strength of Pacific cyclones as an argument for why we should expect increases in the number of major Atlantic hurricanes makes no sense to me.

    What I would like to know is, what do global climate models say about the depth of the warm oceanic layer in the Gulf of Mexico and elsewhere near the U.S., both under the standard assumptions and under assumptions of greater runoff from Greenland which almost all glaciologists seem to find most likely.


    This was well researched keep it up. I am an environmntal journalist from Botswana.

  249. Gerald Machnee:

    RE # 246 – “What were the sea surface temperatures on Andrew’s path?” – working on that, but the site shows what caused the developmet.
    Dr. Nye – How long has he been forecasting hurricanes? Will he describe the formation of Andrew?

  250. wayne davidson:

    That very ill-defined BBC sea temperature graph apparently from NOAA brings up other questions.

    Sea surface temperatures are merely a 2D presentation of 3D events happening below and from far away distances. ENSO is a good example of an “oscillation having a mind of its own”.
    So NOAA’s official thinking appears to be that AMO is going through a warmer phase that will last 10 to 20 years (a forecast as vague as the graph) , I guess I can see that by averaging out anomalous spikes, but this AMO is not at all like ENSO, either ongoing or dormant, brings to mind external influences giving that 1 degree C fluctuation. This graph merely shows 50% of a still undefined story , leaving out the other half, surface and near surface air temperatures. Sea temperatures can be colder or warmer than air at the same buoy locations, would be nice if the other half at the interface between two mediums was presented, and especially with better definitions.

    #249 I’ll listen to a hurricane expert anytime, but Dr Nye deals with Global Climate very well, of which stronger more frequent hurricanes are a mere symptom of a serious problem.

  251. Stephen Berg:

    Re: #239,

    “You say “My thoughts are that ….” Science is not based on ‘thoughts’.”

    Of course, it is. A scientist must observe the results of his/her study and think about what it means. Without this, no conclusions can be made. Science is not based on beliefs, however.

    “If you have evidence that hurricanes have increased in number and intensity in correspondence to CO2 emiissions, please provide a reference.”

    CO2 emissions cannot be THE cause of this increase. However, the overwhelming evidence is that global warming (at least partly a result of increased greenhouse gas-emitting fossil fuel burning) is also resulting in a warming of the oceans, increasing the energy (latent heat) necessary for hurricane formation. The Trenberth, Webster, and Emanuel studies have, by and large, concluded this.

    “What the IPCC TAR report says (Table 1 of ‘The Scientific Basis’) is:

    ‘Increase in tropical cyclone peak wind intensities: Not observed in the few analyses available’

    ‘Increase in tropical cyclone mean and peak precipitation intensities: Insufficient data for assessment'”

    I’d like to emphasize “few analyses available” and “insufficient data for assessment.” As a result of the likely increase in hurricane numbers (according to NOAA forecasts for the next decade at least), studies like Trenberth’s, Webster’s, and Emanuel’s have been undertaken.

    If the likely scenario is that climate change will (at least partly) cause greater numbers of TCs, TSs, and TDs to occur, it is essential that we try to reduce climate change as much as we can so the impacts of these TCs, etc. are minimised. If we do not, then more people will die, more property will be damaged, and greater destabilisation will occur. Governments which do not take these actions will be regarded as negligent to their duties (i.e. to protect their people).

  252. Pat Neuman:

    Ending comments in 250 remind me of a simplification, assumed by many meteorologists, politicians, and the general public, which has been very damaging in the prolonging of a do nothing attitude toward dealing with fossil fuel emissions driven rapid global warming.

    They assume a person knowledgeable in meteorology is knowledgeable about climate change. Climate deals with the atmosphere, but also hydrology, geology, biology, oceans, and the study of Earth’s past. That’s much more than knowledge in modeling and prediction of day-to-day weather. Also, many in the U.S. that are part of the AMS or AASC are meteorologists and/or experts in weather records, not climatologist in the climate change sense. Unfortunately, the media, the policy makers and the general public fail to understand that, and unknowingly accept their skeptical views about global warming as equal to those professional much more qualified in the disciplines needed to understand past climate change, and global warming.

  253. PJK:

    Seems to me that there are two basic facts:

    It is 100% certain that the GW has an impact on each and every single hurricane. No two storms are the same, Even slight changes in the actual weather situation produce a different storm.

    It is also 100% certain that the exact impacts can not be “proven” in the sense that the general public expects, i.e. in this discussion. As you note, it is the same argumentation as in the general climate disussion, all over again.

    My limited contacts with the hurricane research community have made me believe that a hurricane comes in two quite distinct parts:

    Its strength and destructive power depends on its thermodynamic history. The discussion concerning tracks of individual storms crossing specific warm currents in the Gulf is very interesting in this respect. This could be a means of investigating this aspect in a reliable way.

    The path of a storm is driven by the general meteorological process around it. Thermodynamic fields within a radius of a thousand miles steer directly the course it takes. The storm has no internal and independent will in this respect, it is rather like a ball in an old pinball game.

    There was also a response on my previous input concerning the Africa contribution of storm generation. Greening of Africa is indeed predicted by some climate models. This will impact the amount of dust over the Atlantic. This in turn will, then, have an impact on the storms’ early stages of development. Weather modification to suppress hail from thunderstorms is based on the observation that some storms do not have enough condensation nuclei – adding more nuclei changes the convection process as many more and much smaller hailstones are formed at a lower altitude.

    I also attended a conference some 15 years ago where a NHC staff scientist told each and everybody: “bolt them walls to them concrete foundations of your new house, or face disaster when the storm strikes”, with numerous air photos and on-site damage reports to support his admonishment. He also showed detailed results from flooding models on various parts of the Gulf coast. Maybe they did not say specifically that the “levees will be overflown”, though, but a potential flooding disaster in New Orleans was certainly mentioned.

  254. Gerald Machnee:

    RE #250 & #252 – The question remains: What is Dr. Nye knowledgeable in?
    I asked how long has he been forecasting hurricances. In addition what is his training in climatology? What is being assumed about him?
    The problem is not being skeptical about global warming causing hurricanes, but how much to attribute to it. Nobody has been able to come up with a definite percentage since the question of how severe a hurricane becomes is a very complex process.

  255. wayne davidson:


    Fully agree, but basic matter of fact world weather reporting can be dissiminated once in a while by meteorologists. Its the larger picture that most people don’t see which is the problem, if the public is not informed regularly about the larger world, they won’t request the experts you mentionned. We rather see met guys focused on their little corners of the world, but I am certain that most of them know about important world records, which should be passed along to the public in general as often as they come.

    I keep looking at that BBC sea temperature graph lacking meaning traction and comparing it with the PDI graph above and find them incompatible, as if both were displays are from different regions of the world.

  256. Pat Neuman:

    Re 199, on PDI: … “So it’s the wind speed *cubed*, integrated over the surface area covered by the hurricane” … “over the entire area covered by the storm.”

    I would like to see data on surface area covered for the lifetime of tropical storms and hurricanes.

  257. Dan Allan:

    Re #227

    I hope Realclimate takes the opportunity to respond directly to William Gray’s implication that this year’s activity does not represent an anomaly. He is obviously someone who is widely respected, and his assertion that this is part of a normal oscillation is a little hard to fathom. We have had the strongest July storm on record this year, the second strongest August storm on record, and the third strongest September storm. All in the same year. We will also likely have the largest number of named storms ever. This is after last year, which was again one of the busiest hurricane seasons ever. So someone please tell me what past year is similar to this one?

    There seems to be a rather monumental lack of scientific curiosity among those who do not find this a little interesting.

    Nor is “natural oscillation” anything approaching a scientific explanation. What is this oscillation? What causes it? Somebody please explain.

    Finally, to Michael’s J.s’ point regarding Bush’s statement that “nobody could have anticipated the levees to break”.

    Errr…sorry. Forget the Washington Post editorial. Worry about the levees breaking and whether they would hold was the subject of Weather Channel documentary over the summer, an extended series of articles in the New Orleans media drawing on many scientific findings, extensive discussion on CNN in the days leading to landfall, coverage also on every other major news network in the days leading to landfall. In fact, just about the entire country, except apparently the president and one dreadfully mistaken researcher at LSU, worried a great deal that the levees would break. And the president’s comment that nobody could have anticipated it is truly one of the most shocking I have ever heard uttered by a public official in this country.

    [Response: See our response to comment #263. -mike]

  258. betina wolfowicz:

    does anybody know why is a hurricane called “nature’s safety valve?”

  259. Steve Bloom:

    Re #257 (Dan Allan): The article (in paragraph four) was pretty specific in rejecting Gray’s position, albeit without naming him: “…it is wrong to blame any one event such as Katrina specifically on global warming – and of course it is just as indefensible to blame Katrina on a long-term natural cycle in the climate.”

  260. wayne davidson:


    One example of a natural oscillation is a grandfarthers clock pendulum. In this case the pendulum slowly swings once a year , consider the South Atlantic all time temperature average as the vertical, pendulum at rest, with yearly temperatures , swinging to the left (colder), or to the right ( warmer) , last year the pendulum was 0.4 degrees to the right, it seems to be slowly swinging upwards to the right this year. (Hope this helps)….

  261. wayne davidson:

    #184 “would the Northern Pacific ocean warm more?”

    Sorry I missed that , The Atlantic and Arctic Ocean have a lot more in common than with the Pacific,
    you must look at the map and see that they would be considered as one ocean if not named otherwise, while Behring strait severely restricts the Pacific from mixing with the Arctic Ocean. Given this South Atlantic Oscillation fixation by cycle theorists, Is it a wonder why the Pacific region is equally warmer then?

    I second the motion made by #256â¦.

    Iâve joined the BBC graph with the PDI above, and see some semblance getting really confused by the 80âs until 2004. This is likely the graph inspiring the famous 10 to 20 year forecast of increased hurricane activity. Likely of the South Atlantic, perhaps with data from the same geographical area as with the PDI. (A lot of may beâs thanks to the BBC).

    The biggest question that comes to mind, aside from those already mentioned, is why the PDI shoots up almost exponentially way above all previous PDIâs with warmer sea surfaces?

    Yearly Average temperatures of combined Hurricane paths may not offer such confusion, and may reveal a different graph more comparable to the PDI.

  262. Gerald Machnee:

    Re #257 – The North Atlantic Oscillation is explained in the following site as well as others:

    {So someone please tell me what past year is similar to this one?}
    On the following site there is a lot of data on hurricanes over the last hundred years or more. One of the things you will find is that there were a lot of hurricanes(including some very severe ones) in the early 1940’s and also early in the century.
    Re named storms – Hurricanes have only been named since about 1950, so that statement can be confusing.
    Another confusing statistic is numbers of hurricanes or storms. Some count only those making landfall in the USA, some count storms(which may not be of hurricane strength), and others count all storms and hurricanes in the Atlantic whether or not they made landfall.
    Soms scientists have only analyzed the last 30 or 40 years so that analysis will show an increase. If you did a study for the period 1940 to 1975 you would likely show a significant decrease in Hurricanes.
    The NOAA site covers over a hundred years.
    On the following site you will find some Q & A on numbers:
    The year 1933 was the most active.
    The years 1886 and 1887 were very active.

  263. Dan Allan:

    re #260,

    I didn’t mean to suggest that there are not natural oscillations, in climate and of course in many other fields. But I keep hearing very vague statements about “a natural cycle” of hurricane frequency. Yet (a) nobody seems to agree on the exact period of this “cycle”, and (b) nobody seems to be presenting a theory that explains this particular cycle. This makes me very suspicious that the signal for a natural multi-decadal cycle of hurricanes is very strong at all. Finally, I can’t help wondering if we are inferring a “cycle” from a 1 or 1.5 periods. There is obviously a very big difference between “natural variability” and “a natural cycle”. Variability is obvious and quite dramatic in this case. Whether it is cyclical – where is the evidence?

    [Response: There is actually some solid science behind the oft-made claim that there is indeed a multidecadal cycle in Atlantic climate. This includes evidence from instrumental measurements, paleoclimate proxy data, and control simulations of coupled ocean-atmosphere models–see our glossary item on the “Atlantic Multidecadal Oscillation” (AMO). Unfortunately here, as in many cases, the actual science has been overstated, misinterpreted, or selectively used in the public discourse. As we discussed in the current article, the amplitude of this internal oscillation is modest and cannot alone explain the warming trend established, for example, by Emanuel. Moreoever, there is no convincing evidence that long-term changes in Hurricane intensity can be attributed to this cycle. It is therefore as (if not more) irresponsible to tie the unusual number of intense hurricanes this present season to a “natural cycle” as it is to tie it to global warming. Unfortunately, this has not stopped some public commentators. -mike]

  264. BdG:

    An argument is being made that the global warming based prediction that storms would increase in frequency is false because the National Hurricane Center’s records show a reduction in storms.

    I checked the National Hurricane Center’s web site (, in particular, and found that there has indeed been a decrease… in the number of Atlantic cyclones THAT HAVE ACTUALLY ACHIEVED LANDFALL.

    That key phrase is omitted from the popular argument. The upshot is that while there have been fewer storms that have struck the US, nothing can be concluded regarding any changes (relative to the time period pre-1960 when there were no weather satellites) in total numbers or even ferocity. Maybe there were fewer storms, maybe there were more. Maybe they were weaker, maybe they were nastier. Frankly, nobody knows.

  265. Michael Jankowski:


    I simply think his comment was poorly worded and/or taken out-of-context, and I don’t quite see why it was included in the report in question other than for badgering.

    The vast majority of reports/predictions I have seen suggested the levees would not fail, even under a Category 5 with a similar path to Katrina. I think this is in-line with what he said, or what he intended by what he said. Maybe “nobody” was a poor choice of words, but I don’t think it was meant to be taken literally or should have been taken literally. Along those same lines, I can say that “everyone” knows that a structural failure can occur in any object at any time, especially a levee in a rain/flood/hurricane event.

    I hear rumblings of local and state officials neglecting levee project funding, improper and unaccounted spending by the Louisiana Office of Homeland Security and Emergency Preparedness (along with federal indictments), etc.

    There’s a lot of finger-pointing and blame to go around, but not a lot of serious talk about solutions.

  266. Gerald Machnee:

    Re # 263 – the hurricanes do not follow a “natural” cycle. However the temperatures in the Atlantic where the hurricanes form have a cycle which is about 30-50 years in length. When the temperatures are warmer there are more hurricanes and likely more stronger ones. The temperatures and hurricanes were up in the 1940’s then down in the 1970’s. At this time the temperatures are higher and we are seeing more activity. This has been predicted to continue for several more years. Re # 264 – while more hurricanes were predicted for this year, it is really difficult to predict how many will make landfall. The sites I noted in #262 give numbers of hurricanes in various years. Thr following site has year by year totals:
    The BBC site gave average Atlantic temperatures.

  267. Dan Allan:

    re #266 – Thanks.

    This is the closest I have heard to something specific. But it still raises some questions:

    (1) how many of these 30-50 year periods have we observed and measured, that we can be confident in this cycle? And (2) do this year’s SSTs appear to be within range of a high SST period, or are they anomalously high, even for a warm period?

    [Response: See our response to comment #263. -mike]

  268. Gerald Machnee:

    Re #267 – re your first question – an interesting article appeared in the St. petersberg times in September:

    Re (1) – Fishermen had tracked the temperatures. Then scientists checked tree rings and found that the cycle went back hundreds or a thousand or more years.
    Re (2) – According to the hurricane forecasters, we are somewhere in the middle of the (warm) cycle. Of course there could be variations in the number of events, e.g. we know that winter will be colder, but the daily temperatures could vary by 20 degrees and we do not know exactly how many storms will develop to very severe ones.

  269. Siobhan Sullivan:

    one problems with blaming increased hurricane activity on global warming is that weather patterns tend to last up to twenty years before they change. There appears to be little doubt that warmer waters fuel hurricanes to catagory 5 status, if teperatures in general
    continue to increase then the intensity of storms will increase.

  270. Dan Allan:

    Mike and Gerald –
    Thanks for the responses to 263. Makes sense. I probably should have read the article more carefully before shooting off.

    Nonetheless, one point still stands – there is a great deal of overstated attribution of this season’s hurricanes to multi-decadal cycles.

    I heard one expert on TV (I think it was Max Mayfield) actually say that “this was just a return to normal.” DIfficult to see how what is likely to be the busiest / most severe season ever (if one uses a simple metric such as multiplying each named storm times maximum category, and then summing) could be seen as “normal”. Maybe it is truly attributable to mult-decadal cycle, or 99% attributable, but the lack of scientific curiosity is a little strange.

  271. wayne davidson:


    Nonsense going unchallenged is a very bad thing.

    Lets accept, very temporarily, that there was a weak but identifiable average temperature oscillation of the Sourth Atlantic, today it is no longer the same.. Why? If a grandfather clock pendulum cable is shortened or lengthened, the frequency of the said grandfathers clock changes . A physical change has occured, no longer the same effect can happen. And so goes the South Atlantic temperature oscillation. The air above, especially CO2 forcing is not the same, there is no such thing as returning to “normal” , we don’t live on a planet having identical closed system parameters through time, everything changes especially now a days, and once upon cycles, real or not, get transforned. I think it is simply wishful thinking to assume that every thing can return to normal when the very shape of the Earth’s coastal shores and atmosphere has changed. The concept of regular meso-cycles can apply for a distant planet devoid of inhabitants, like Mars or Venus. Perhaps they can be found there.

  272. Gerald Machnee:

    Re #270 – I think what Max Mayfield meant is that the numbers are “normal” or “average” for a high SST cycle. Most of the last 10 years have had a high number of storms, but 2 of the years were low. There was also about 10 years with no landfalls. So having a couple of landfalls this year is not out of the ordinary. A normal or average is the sum of events over a number of years divided by the number of years. So you can expect some to be higher and others to be lower. So a bit above the average is close to normal. They have said that we are in a higher occurrence cycle.
    Similarly normal temperatures are obtained by adding up the (highs, lows) and dividing by thr number of years. Some countries use 30 years for doing averages. We do not see a “normal” temperature very often. This is what makes the study so interesting and exciting.

  273. Ike Solem:

    I don’t understand why the larger issue of net equator-to-pole heat transfer, of which hurricanes can be seen as just one component, is not being brought up here. Rather then asking if global warming is responsible for hurricane frequencty/intensity increases, isn’t the more important (and more accessable) question, is global warming responsible for increased sea surface temperatures, including (importantly for hurricanes) depth profiles? I’d like to know what the predictions for equator to pole heat transfer changes are in global warming models…

    [Response: SSTs are indeed studied, Barnett et al. “Penetration of Human-Induced Warming into the World’s Oceans” (Science, Vol 309, Issue 5732, 284-287, 8 July 2005), say that the observed warming of the oceans cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two anthropogenically forced climate models. We conclude that it is of human origin, a conclusion robust to observational sampling and model differences. Note, BTW, that std theory would suggest a *diminished* pole-to-eq temperature gradient under GW, since the poles warm faster (at equilibrium) and the North Pole warms faster in transient runs too – William]

  274. Dan Allan:

    Re 272:

    Gerald, even if I accept your interpretation of Mayfield’s language, that he was referring to the last several years of activity rather than just this year, I would still have to quibble with what he said. A “return to normal” clearly implies that the low-hurricane years that preceded the last several were “abnormal”. But using your same method of averaging over several years, wouldn’t you find that these years were “normal” as well? By implying that this period is normal, and the previous quiet period is not, he is effectively preparing us for a future of high hurricane incidence, while avoiding any possible attribution to AGW.

  275. J. Sperry:

    Re #270

    I heard one expert on TV (I think it was Max Mayfield) actually say that “this was just a return to normal.” DIfficult to see how what is likely to be the busiest / most severe season ever (if one uses a simple metric such as multiplying each named storm times maximum category, and then summing) could be seen as “normal”. Maybe it is truly attributable to mult-decadal cycle, or 99% attributable, but the lack of scientific curiosity is a little strange.

    I did this analysis, since I’ve heard of this kind of index (though Iâ??m not sure how much climatologists use it) and already had most of the data available. Including all Atlantic hurricanes (I donâ??t like to limit data to only hurricanes making landfall, as some do), 2005 is currently close to or less than at least 10 years in the last century. Using this index, the average is around 11-14, and the following years are over an index of 24:
    2004, 1999, 1995,
    1969, 1961, 1955, 1950,
    1933, 1926, 1916 (these include storms recorded before naming began)

    Aside from the (intentional) grouping of years above, I canâ??t help but notice the back-to-back years for 2004-05. However, we still have a ways to go to reach the 1950 level (e.g., two Cat. 3 and a Cat. 1 would do it). There is also an Accumulated Cyclone Energy (ACE) index, which also shows a projected range for 2005 that is similar to 9 years since 1950. (Again, we have a ways to go to reach the levels of 2004, 1995, and 1950 using this index).

    Of course, these are all different from the PDI in Fig. 2 of the original article above. I wonder what RealClimateâ??s thought is on how these other indexes compare with the PDI in determining any trend in hurricane activity.

  276. Gerald Machnee:

    Re # 272, 274 – If Mayfield meant that this year is a longtime normal, then I would probably disagree or say he is misquoted. The site from NOAA with FAQ gives numbers for over a hundred years and I believe there is an “average” calculation. The study by Emmanuel is limited in that it begins in a lower number and ends in years with a high number. He used satellite data which means he could not look at data in the 1940’s or at the end of the last century.

    [Response: I would suggest that you re-read the Emmanuel article. Nowhere in the article does he even mention satellite data. His analysis was based on historical wind observations which date back to the mid 1940s. The relationship between the PDI he calculates from these data, and SSTs over the appropriate season and region of the tropical Atlantic is strong enough that one would suspect it is likely to hold further back in time–the trend in the most recent decade is unmatched in this SST history back into the mid 1930s.

    Perhaps you are thinking of a more recent study in Science by Webster et al which comes to very similar conclusions regarding trends between SSTs and Hurricane intensities, based on a shorter, but entirely independent (yes–satellite-based) dataset. -mike]

  277. Gerald Machnee:

    Re #276 – Yep – I was probably referring to Webster. Thanks.

  278. Pat Neuman:

    From ABC World News Tonight…

    POINT BARROW, Alaska, Sept. 27, 2005 â?? This season has ushered in the warmest Arctic summer in 400 years. A NASA report to be released this week finds the polar ice pack has shrunk by nearly 30 percent since 1978, and new satellite photos show the melting is speeding up. …

    In responding to the general public:

    How significant is the rapid thaw in the Arctic for hurricane development?

  279. Dan Allan:


    If you have a handy link where you got info on hurricane frequency / intensity by year, I’d be interested.



  280. Gerald Machnee:

    Re # 279 – The following site has named storms, hurricanes, strong ones – level 3,4,5 and ACE which is a calculation of energy.
    Is this what you need? It has yearly totals to 2003.

  281. Deborah:

    this is all very alarming. In 500 years from now the Earth would probably be inhabitable, it would be too hot. I think based on estimates we would be gaining 5-10 degrees per century, and when we pass the critical point, the increase in temperature will exponentiate. Does anyone know of an article that can clarify the temperature increase in the next 100-500 years?

  282. wayne davidson:


    Someone above said there was no link between Polar Ice melting and stronger hurricanes, absurd as it may sound for environmental experts, it may be the prevailing vu from a great many people. They are not totally at fault for thinking likewise, because I have yet to read in the public discourse or from many media outlets, that this summer was the warmest in history for the Northern Hemisphere, at least from May till August, however many people hearing this would make the connection immediately by themselves: warmest summer = stronger hurricanes. I wonder if Mr Gray mentioned this during his Senate appearance? Movie stars personal lives still overwhelm the news channels, so there is plenty of time to report something serious. This is the greatest weather lack of reporting scandal of all time, with all these outlets, hundreds if not thousands of met media specialists, somehow oblivious to this fact. I am deeply puzzled by why this is not reported.

  283. Gerald Machnee:

    Re # 282 – The answer is simple – that type of correlation is not science, but more like gossip. Have you checked all the past high hurricane seasons since 1850 to see if that is true?

  284. Richard Wesley:

    Re: 279

    Complementing the data mentioned in #280, I have links to both the raw NOAA Atlantic hurricane records and a MySQL import file of a slightly cleaned up version of that data here. The page includes descriptions of the cleaning and how to reproduce the Emanuel PDI calculation for the Atlantic from the data. As soon as I get a chance to hack trig functions into Tableau, I will update the page with Emanuel’s corrections.

    The ACE page sounds interesting and I will have a look at it. Does anyone know if it is derivable from the raw observational data? I would presume so, but I haven’t looked at the page in any detail yet.

  285. Richard Wesley:

    Re #284

    I’m an idiot. ACE is almost the same as PDI except that it is a square, not a cube. Another fun graph to make ;-)

  286. Dan Allan:

    Gerald, re #280 –

    didn’t find any data there for 2004 or 2005, but was able to show that 1994 thru 2003 was the most intense period (though not by a lot) since good data became available in 1944 (according to the site “ACE” method, which seemed reasonable. As 1994 was a very quite year and 2004 and 2005 very busy, I suspect that the ten year period 1996-2005 would be more obviously more intense than any previous 10 year period for which we have good data – maybe not dramatically more intense, but then, given the degree of GW experienced so far, I’m not sure we’d expect anything that dramatic yet. Maybe we lack enough data to draw a firm statistical conclusion or to confidently infer an the effects of GW – but the data is at least strongly suggestive to my lay-person’s eyes.

    – Dan

  287. Stephen Berg:

    Re: #283,

    The correlation between warmer summers and stronger hurricane seasons makes some scientific sense, being that warmer summers have greater energy with which to work, which increases the strength of and leads to more frequent occurrence of such storms. Also, warmer summers increase (slightly) the SSTs of any water body which is affected by the higher temperatures, providing more fuel to the equation (leading to stronger and more frequent TDs, TSs, and TCs).

    It is scientific, not gossip, this correlation. Please stop sounding like Sen. Inhofe. You are and can do better than that.

  288. Gerald Machnee:

    Re 285 –
    Try this site:

    just change the year at the end to check on 2004, etc.
    It is up to date for this year. looks nice

  289. wayne davidson:


    Gossip???? You must be joking…. South Atlantic SST’s got boosted along with Lake Ontario’s surface lake temperature along with all the Arctic ice all time melt… Playing with statistics can’t possibly surpass these events actually happening now…. It is simple, it is warmer everywhere. If someone wants to complicate this image, then the motivation must be inspired by contrarian musings as usual, confusion is so much more better than a grasp of reality.

  290. Gerald Machnee:

    Re #287 – The statement was made correlating melting ice and hurricanes for one year – THAT is not science. At the end I suggested checking from 1850 to the present for a correlation – that is a bit more scientific. You will note that 2002 was a warm year with little activity. There is more to hurricane formation than warm weather.

  291. Pat Neuman:

    Re 282

    I think the greatest reporting scandal of all time is the lack of accurate information on anthropogenic enhanced global warming and it’s primary cause is fossil fuel burning.

    For example.

    A public comment was made this morning by meteorologist Jonathan Yuhas* on the release by NSIDC and NASA on: Sea Ice Decline Intensifies.

    Mr. Yuhas commented that he doesn’t know how they’re going to melt ice in total darkness in winter. The remark had a tone of skepticism toward the report and skepticism toward global warming.

    Mr. Yuhas has voiced his skepticism on global warming many times in the past. Should Mr. Yuhas and other weather-casters be blamed? Why are meteorologists and weather-casters so “in the dark” about global warming? Who is responsible for getting the facts on climate change to the meteorologists and weather-casters who broadcast the day to day information about weather and climate records? For many people, all they listen to from day to day are daily weather reports on TV or radio.

    * KARE11 in the Twin Cities.

  292. Gerald Machnee:

    RE 3 291 – “accurate information on anthropogenic enhanced global warming”.
    The reason it is difficult to have “accurate” information is because it is impossible to measure it with instruments. What you have is theories and statistical association.

  293. Stephen Berg:

    Re: #292,

    The accurate information is there. However, news station editors filter it out because it is seen by the elite to be subversive and will result in the pulling of advertising (and money) from the stations which include unbiased information (à la Mann, Bradley, and Hughes).

    Investigative reporters like Ross Gelbspan are often featured on these stations. However, the networks think they need to achieve balance by putting a skeptic (whose only purpose is to confuse or obfuscate the public) following a Gelbspan or one of MB&H. This is appalling, since it injects bias into their newscasts.

    No, Gerald, the information is there. It just isn’t getting out.

  294. Pat Neuman:

    Re 291, 292, 293

    I think these links show accurate information on anthropogenic enhanced global warming.


  295. Gerald Machnee:

    Re # 294 – What the links you listed show are mainly temperature trends and changes. They do not calculate the percentage change that may be due to AGW. It still remains a theory based on statistical association that has been programmed into computer models and is used to forecast a future warming. The third reference has a lot of reprint from the IPCC which will likely be challenged for their next report.
    So if the temperature at New York was 68 deg F, you cannot tell me what part is due to AGW, even though you think some of it is. That is what I meant by accurate information (Calculation)
    You cannot tell me whether the temperatures will increase or decrease next year. If AGW was that significant or measureable you would expect temperatures to increase every year or you could calculate the change.

  296. Tanja:

    Doesn’t hurricane Catarina indicate a connection between warming and hurricanes? The only one to ever hit the Southern Atlantic (Brazil).
    Apparently theoretically no hurricanes should form in this area.

  297. Gerald Machnee:

    Re # 296 – Why would Catarina indicate a connection? It is more historically than theoretically that there have been none or few recorded events. There were two tropical storms in the area. That is an area with a lack of recording sites. When Catarina occurred was cooler than usual- so would that indicate that global warming was responsible? Tropical storms do form in the southern hemisphere – when conditions are right.

  298. Dan Allan:

    Re #295 –


    A couple of things. First, it is possible to be accurate or inaccurate in the reporting of a theory. No? A perfect example is in your own email. You state: “If AGW was that significant or measureable you would expect temperatures to increase every year or you could calculate the change.” This is an example of a false statement about the theory of AGW. Within the year-to-year timescale, natural variability caused by many factors other than AGW can cause temporary decreases in temperate. This is forecast and expected by all global climate models.

  299. Stephen Berg:

    Re: #297,

    It indicates a connection, since, over the last few centuries (since people have been inhabiting the coast of Brazil in rather large numbers), no TCs had ever been recorded.

    This is likely due to SSTs being sufficiently warm for the formation of these storms when previously, the SSTs inhibited TC/TS/TD formation. This would lead most scientists to conclude that the oceanic warming needed for storm development is likely due to human-induced climate change.

    As for “a lack of recording sites,” sure there may not have been many meterological stations at that time. However, there are PEOPLE who can record these events in diaries, newspapers, journals, logbooks, etc. A met-station is not the only way to collect data, Gerald.

    Also, as for:

    “When Catarina occurred was cooler than usual- so would that indicate that global warming was responsible? Tropical storms do form in the southern hemisphere – when conditions are right.”

    Maybe atmospheric temperatures were cooler than normal. However, SSTs were likely not!

    Also, TSs “do form in the southern hemisphere – when conditions are right.” However, they are so unlikely over the area Tanja (#296) had referred to (if not theoretically impossible, at least in the past) due to the cooler-than-necessary SSTs (i.e. less than 26 C). Now that SSTs have risen in this area (at least partly a result of human-induced climate change), these storms will likely occur with greater frequency (and intensity down the road).

  300. Pat Neuman:

    Re # 294


    I think the text and links that follow address some of the elementary questions about global warming that you may still have. …
    How much has the amount of CO2 in the atmosphere changed in history?
    The figure below show results of CO2 measurements of air trapped in ice cores taken at the Law Dome site in Antarctica, along with present day measurements at the CMDL Mauna Loa Observatory in Hawaii. CO2 amounts have increased about 35% in the last 200 years.

    El Niño is a natural phenomenon that has been occurring throughout the centuries, though not always with the same regularity; it now occurs about every two to seven years. El Niño is the strong warming of the equatorial Pacific ocean. Its effects are felt worldwide, which demonstrates the interconnected nature of the Earthâ??s climate. … Scientists are concerned that the accumulation of greenhouse gases in our atmosphere may inject enough heat into the Pacific Ocean to make El Niño events more frequent and fierce.

    Declining Arctic Sea Ice:

    Earlier Midwest Spring Snowmelt Runoff

    Global Land Air Temperature ten yr mov avgs

  301. JimG:

    I am not sure if I believe the “Hurricane results in a Net Gain for the Economy” line of reasoning, since the money spent on fixing hurricane damage, could be spent instead, say, on installing solar panels, if there were no hurricane damage, and installing solar panels would help to mitigate global warming, while fixing what breaks does not mitigate global warming.

    200 billion in solar panels, and their installation, would make a big difference, and would create just as many construction jobs and manufacturing jobs, as hurricane damage re-construction. (It’s what economists call the “opportunity cost” which this “net gain for the economy” reasoning misses.)

  302. Gerald Machnee:

    Re # 298 – I was not questioning the reporting of a theory – you are making the issue complicated – I was saying that measuring the amount of GW or AGW is difficult or almost impossible with instruments — that’s it!
    Re # 300 – Again I am not saying that CO2 or other parameters are not changing or we are not measuring them. However, CO2 is small compared with water vapor in the atmosphere, so therefore the total change in greenhouse gases is not as great as the change in CO2. So if CO2 changes 35 percent, the change in greenhouse gas total is less than a percent. Anyway, my point is the same as above – hard to measure the exact amount of influence – good career opportunity!!
    RE # 299 – “It indicates a connection, since, over the last few centuries (since people have been inhabiting the coast of Brazil in rather large numbers), no TCs had ever been recorded.

    This is likely due to SSTs being sufficiently warm for the formation of these storms when previously, the SSTs inhibited TC/TS/TD formation. This would lead most scientists to conclude that the oceanic warming needed for storm development is likely due to human-induced climate change.”

    I have not looked at this area in detail which is why I opened with a question in my response. In other words – Has the SST increasd? When I noted lack of reporting sites, I was quoting from scientific reports. You indicated that people have been living there a long time – but the scientists noted a lack of reports. You have to realize that the records there may not be as good as in North America. To have a report on the coast – the storm has to make landfall. One report noted that there may have been less ship activity therre compared with the north Atlantic so less storms may have been encountered. Even if SST is high enough, you still need the right meteorological conditions to form the storm or hurricane. I believe that there is less cyclone activity in the southern hemisphere than the north.
    “Maybe atmospheric temperatures were cooler than normal. However, SSTs were likely not! ”
    This report came from scientists who noted the cooler conditions. Have you checked the SST’s? Scientists did indicate that they would have to rely more on satellite photos for observing activity.

  303. Gerald Machnee:

    Further to Catarina, the following quote is from a UCAR site:

    “Already, southern Brazil’s summer had been a strange one. “January and February 2004 were the coldest in 25 years,” notes modeler Pedro Leite da Silva Dias (University of Sao Paolo). Although Catarina was later tagged by some as a possible sign of climate change, the waters over which it formed were actually slightly cooler than average. However, “the air was much colder than normal,” says Dias. This produced the same type of intense upward heat flux that fuels hurricanes, normally seen in warmer waters.”

    Other sites indicate that one of the main reasons for a lack of hurricanes there is the wind shear is too great.
    You can find studies on this hurricane by searching “Hurricane Catarina”

  304. weblog:

    New Investigation of the Global Warming – Hurricane Connection
    For better or worse, the 2005 hurricane season generated a lot of interest in the link between global warming and hurricanes. A new study published this week in Science Express attempts to further nail down the link between warmer ocean…

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