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Hurricanes and Global Warming – Is There a Connection?

Filed under: — group @ 2 September 2005 - (Français) (Español)

by Stefan Rahmstorf, Michael Mann, Rasmus Benestad, Gavin Schmidt, and William Connolley

On Monday August 29, Hurricane Katrina ravaged New Orleans, Louisiana and Missisippi, leaving a trail of destruction in her wake. It will be some time until the full toll of this hurricane can be assessed, but the devastating human and environmental impacts are already obvious.

Katrina was the most feared of all meteorological events, a major hurricane making landfall in a highly-populated low-lying region. In the wake of this devastation, many have questioned whether global warming may have contributed to this disaster. Could New Orleans be the first major U.S. city ravaged by human-caused climate change?

The correct answer–the one we have indeed provided in previous posts (Storms & Global Warming II, Some recent updates and Storms and Climate Change) –is that there is no way to prove that Katrina either was, or was not, affected by global warming. For a single event, regardless of how extreme, such attribution is fundamentally impossible. We only have one Earth, and it will follow only one of an infinite number of possible weather sequences. It is impossible to know whether or not this event would have taken place if we had not increased the concentration of greenhouse gases in the atmosphere as much as we have. Weather events will always result from a combination of deterministic factors (including greenhouse gas forcing or slow natural climate cycles) and stochastic factors (pure chance).

Due to this semi-random nature of weather, 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.

Yet this is not the right way to frame the question. As we have also pointed out in previous posts, we can indeed draw some important conclusions about the links between hurricane activity and global warming in a statistical sense. The situation is analogous to rolling loaded dice: one could, if one was so inclined, construct a set of dice where sixes occur twice as often as normal. But if you were to roll a six using these dice, you could not blame it specifically on the fact that the dice had been loaded. Half of the sixes would have occurred anyway, even with normal dice. Loading the dice simply doubled the odds. In the same manner, while we cannot draw firm conclusions about one single hurricane, we can draw some conclusions about hurricanes more generally. In particular, the available scientific evidence indicates that it is likely that global warming will make – and possibly already is making – those hurricanes that form more destructive than they otherwise would have been.

The key connection is that between sea surface temperatures (we abbreviate this as SST) and the power of hurricanes. Without going into technical details about the dynamics and thermodynamics involved in tropical storms and hurricanes (an excellent discussion of this can be found here), the basic connection between the two is actually fairly simple: warm water, and the instability in the lower atmosphere that is created by it, is the energy source of hurricanes. This is why they only arise in the tropics and during the season when SSTs are highest (June to November in the tropical North Atlantic).

SST is not the only influence on hurricane formation. Strong shear in atmospheric winds (that is, changes in wind strength and direction with height in the atmosphere above the surface), for example, inhibits development of the highly organized structure that is required for a hurricane to form. In the case of Atlantic hurricanes, the El Nino/Southern Oscillation tends to influence the vertical wind shear, and thus, in turn, the number of hurricanes that tend to form in a given year. Many other features of the process of hurricane development and strengthening, however, are closely linked to SST.

Hurricane forecast models (the same ones that were used to predict Katrina’s path) indicate a tendency for more intense (but not overall more frequent) hurricanes when they are run for climate change scenarios (Fig. 1).

Figure 1. Model Simulation of Trend in Hurricanes (from Knutson et al, 2004)

In the particular simulation shown above, the frequency of the strongest (category 5) hurricanes roughly triples in the anthropogenic climate change scenario relative to the control. This suggests that hurricanes may indeed become more destructive (1) as tropical SSTs warm due to anthropogenic impacts.

But what about the past? What do the observations of the last century actually show? Some past studies (e.g. Goldenberg et al, 2001) assert that there is no evidence of any long-term increase in statistical measures of tropical Atlantic hurricane activity, despite the ongoing global warming. These studies, however, have focused on the frequency of all tropical storms and hurricanes (lumping the weak ones in with the strong ones) rather than a measure of changes in the intensity of the storms. As we have discussed elsewhere on this site, statistical measures that focus on trends in the strongest category storms, maximum hurricane winds, and changes in minimum central pressures, suggest a systematic increase in the intensities of those storms that form. This finding is consistent with the model simulations.

A recent study in Nature by Emanuel (2005) examined, for the first time, a statistical measure of the power dissipation associated with past hurricane activity (i.e., the “Power Dissipation Index” or “PDI”–Fig. 2). Emanuel found a close correlation between increases in this measure of hurricane activity (which is likely a better measure of the destructive potential of the storms than previously used measures) and rising tropical North Atlantic SST, consistent with basic theoretical expectations. As tropical SSTs have increased in past decades, so has the intrinsic destructive potential of hurricanes.

Figure 2. Measure of total power dissipated annually by tropical cyclones in the North Atlantic (the power dissipation index “PDI”) compared to September tropical North Atlantic SST (from Emanuel, 2005)

The key question then becomes this: Why has SST increased in the tropics? Is this increase due to global warming (which is almost certainly in large part due to human impacts on climate)? Or is this increase part of a natural cycle?

It has been asserted (for example, by the NOAA National Hurricane Center) that the recent upturn in hurricane activity is due to a natural cycle, e.g. the so-called Atlantic Multidecadal Oscillation (“AMO”). The new results by Emanuel (Fig. 2) argue against this hypothesis being the sole explanation: the recent increase in SST (at least for September as shown in the Figure) is well outside the range of any past oscillations. Emanuel therefore concludes in his paper that “the large upswing in the last decade is unprecedented, and probably reflects the effect of global warming.” However, 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. Previous analysis of the AMO and natural oscillation modes in the Atlantic (Delworth and Mann, 2000; Kerr, 2000) suggest that the amplitude of natural SST variations averaged over the tropics is about 0.1-0.2 ºC, so a swing from the coldest to warmest phase could explain up to ~0.4 ºC warming.

What about the alternative hypothesis: the contribution of anthropogenic greenhouse gases to tropical SST warming? How strong do we expect this to be? One way to estimate this is to use climate models. Driven by anthropogenic forcings, these show a warming of tropical SST in the Atlantic of about 0.2 – 0.5 ºC. Globally, SST has increased by ~0.6 ºC in the past hundred years. This mostly reflects the response to global radiative forcings, which are dominated by anthropogenic forcing over the 20th Century. Regional modes of variability, such as the AMO, largely cancel out and make a very small contribution in the global mean SST changes.

Thus, we can conclude that both a natural cycle (the AMO) and anthropogenic forcing could have made roughly equally large contributions to the warming of the tropical Atlantic over the past decades, with an exact attribution impossible so far. The observed warming is likely the result of a combined effect: data strongly suggest that the AMO has been in a warming phase for the past two or three decades, and we also know that at the same time anthropogenic global warming is ongoing.

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.

References:

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.


317 Responses to “Hurricanes and Global Warming – Is There a Connection?”

  1. 201
    Steve Bloom says:

    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.

  2. 202
    Chris Reed says:

    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.

  3. 203

    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.

  4. 204
    Michael Jankowski says:

    Re#203,
    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.

  5. 205
    Lynn Vincentnathan says:

    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?

  6. 206
    Lynn Vincentnathan says:

    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.

  7. 207
    ba says:

    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.
    http://www.bbc.co.uk/science/horizon/2002/freakwave.shtml
    http://www.smh.com.au/articles/2004/07/25/1090693835341.html

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

  8. 208
    Dan Allan says:

    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.

    Thanks.

  9. 209
    Steve Bloom says:

    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.

  10. 210

    #204

    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.

  11. 211
    Lynn Vincentnathan says:

    #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.

  12. 212
    Michael Jankowski says:

    ***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?

  13. 213
    Hank Roberts says:

    Here’s that ‘Loop Current’ charted

    http://oceancurrents.rsmas.miami.edu/caribbean/loop-current.html

  14. 214
    Pat Neuman says:

    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:
    http://groups.yahoo.com/group/ClimateArchive/message/1853

  15. 215
    GJ says:

    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.

  16. 216

    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.

    #212

    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.

  17. 217
    Steve Bloom says:

    Folks may be interested in a small debate I’m having with RP Sr. over at http://climatesci.atmos.colostate.edu/?p=53 . 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?

  18. 218

    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,

    http://www.sciencemag.org/cgi/content/full/307/5716/1769

    and

    http://www.sciencemag.org/cgi/content/full/307/5716/1766

    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.

  19. 219
    Pat Neuman says:

    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.

  20. 220
    Joseph O'Sullivan says:

    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
    http://www.progressiveregulation.org/articles/CPR_Special_Levee_Report.pdf

    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.

  21. 221
    Stephen Berg says:

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

    http://edition.cnn.com/2005/WEATHER/09/23/climate.scientist.reut/index.html

  22. 222
    Michael Jankowski says:

    Speaking of meteorologists opening their mouths http://www.prisonplanet.com/articles/september2005/080905russianinventors.htm

    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.” http://www.nola.com/hurricane/index.ssf?/washingaway/thebigone_1.html . 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 http://www.freerepublic.com/focus/f-news/1479991/posts , which does contain the scientific opinion from an LSU researcher that the floodgates would have been of great benefit.

  23. 223

    # 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.

  24. 224
    Joseph O'Sullivan says:

    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!

  25. 225
    PJK says:

    #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 Accuweather.com 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 …

  26. 226

    #225

    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.

  27. 227
    Mark Trexler says:

    A major piece on climate change and hurricanes appeared at cnn.com 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.”

  28. 228
    Steve Bloom says:

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

  29. 229
    Stephen Berg says:

    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.

  30. 230
    Michael Jankowski says:

    “#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 http://www.washingtonpost.com/wp-dyn/content/article/2005/09/13/AR2005091302196.html, 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 http://www.nola.com/washingaway/risk_1.html and here http://www.commondreams.org/headlines05/0916-10.htm . 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.

  31. 231
    Gerald Machnee says:

    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.

  32. 232

    #227,

    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):

    http://edition.cnn.com/2005/TECH/science/09/01/katrina.warming.ap/

  33. 233
    Bob Holloway says:

    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.

  34. 234
    PHEaston says:

    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.

    http://news.bbc.co.uk/1/hi/sci/tech/4276242.stm

  35. 235
    Pat Neuman says:

    “the chance is 1 in a 1000″

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

    Excerpts:

    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

    http://zfacts.com/p/49.html

  36. 236
    Stephen Berg says:

    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.

  37. 237
    Ed Erpelding says:

    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.

  38. 238
    ba says:

    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.

  39. 239
    PHEaston says:

    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.

  40. 240
    TCO says:

    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?

  41. 241

    #234,

    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.

  42. 242
    Gerald Machnee says:

    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.

  43. 243
    Steve Hollingsworth says:

    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?

  44. 244

    #242,

    “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.

    also

    “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?

  45. 245
    Gerald Machnee says:

    RE# 242-244: If you read the history of Andrew at: http://www.nhc.noaa.gov/1992andrew.html 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.

  46. 246

    # 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…..

  47. 247
    B Johnston says:

    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.

  48. 248

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

  49. 249
    Gerald Machnee says:

    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?

  50. 250

    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.


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