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  1. Your links for the “dissenting” camp lead to the non-dissenting camp.

    Comment by jae — 20 Mar 2006 @ 6:58 PM

  2. Thank you for the update on potential influences of climate disruption on tropical cyclones.

    I agree mostly with Roger Pielke, Jr. (on this one issue…); in general I suspect that for the US, the ‘rush to tropical coastlines’ has, and is likely to continue having a much bigger impact than the AGW-induced intensity rise. However, the US is not the world, and for parts of the world where moving away from the coast is not an option (e.g. Bangladesh), this is a very serious danger.

    Also – even the US, should the ‘rush to tropical coastlines’ continue, it will, I fear, combine synergisticly with any AGW-induced increased in intensity.

    Comment by llewelly — 20 Mar 2006 @ 7:07 PM

  3. Good post.

    In Chicago 2 weeks ago, the Association of American Geographers met, and the Climate Specialty Group hosted several hurricane sessions, including this talk from Davis, Knappenberger and Michaels:

    Trends in Hurricane Intensity and Linkages to North Atlantic Sea-Surface Temperatures

    abstract:

    Several papers have suggested rising sea surface temperatures (SSTs) in the North Atlantic hurricane formation region are linked to recent increases in hurricane activity, and that the trend of rising SSTs during the past 3 to 4 decades bears a strong resemblance to that projected to occur from increasing greenhouse gas concentrations. However, none of these studies have directly linked the changes in SSTs to changes in hurricane intensity. Rather, they rely on trends in basin-wide averaged monthly or seasonal SSTs that are not necessarily representative of the local marine environment experienced by tropical cyclones. We demonstrate a direct connection between SST and hurricane strength. We match the 6-hourly positions from each named tropical system in the North Atlantic with the observed weekly averaged SST from the 1º latitude x 1º longitude grid cell that contained the storm’s center, during the hurricane seasons of 1982 through 2004. We identify the maximum SST encountered by each system prior to the time that the storm reached its maximum intensity. When we examine the relationship between SST and intensity, we find that although SSTs contribute significantly to tropical cyclone activity, their influence varies markedly over time. Further, we find a step-like, rather than a continuous, influence of SST on cyclone strength, suggesting that there exists a SST threshold which must be crossed before tropical cyclones develop into major hurricanes. These findings highlight the complex nature of hurricane development and counter arguments of a simple cause-and-effect relationship between rising SSTs and stronger Atlantic hurricanes.

    To get to the citation and to link to other papers in the session:
    http://tinyurl.com/j26y8

    I cannot remember where they have sent their paper, but it did not create as many murmurs as probably all of us were expecting. I think they identified 28.x C as a critical threshhold for SST, below which cat 3 was unlikely, but above which the distribution of cat 3-4-5 become random rather than linear as SSTs increase (at least it was unpredictable beyond the critical threshold). Something like that. Also note they use 1982-2004 data, rather than the earlier set.

    [Response: Interesting… I wonder if K&M wrote the last sentence ;-) – William]

    Comment by Kenneth Blumenfeld — 20 Mar 2006 @ 7:45 PM

  4. What does one make of the USGS press release:
    “Century of Data Shows Intensification of Water Cycle but No Increase in Storms or Floods”
    http://www.usgs.gov/newsroom/article.asp?ID=1475
    Released: 3/15/2006 12:13:21 PM”
    […]
    A review of the findings from more than 100 peer-reviewed studies shows that although many aspects of the global water cycle have intensified, including precipitation and evaporation, this trend has not consistently resulted in an increase in the frequency or intensity of tropical storms or floods over the past century. The USGS findings, which have implications on the effect of global climate change, are published today in the Journal of Hydrology.

    “A key question in the global climate debate is if the climate warms in the future, will the water cycle intensify and what will be the nature of that intensification,” said USGS scientist Thomas Huntington, who authored the study. “This is important because intensification of the water cycle could change water availability and increase the frequency of tropical storms, floods, and droughts, and increased water vapor in the atmosphere could amplify climate warming.”

    For the report, Huntington reviewed data presented in more than 100 scientific studies. Although data are not complete, and sometimes contradictory, the weight of evidence from past studies shows on a global scale that precipitation, runoff, atmospheric water vapor, soil moisture, evapotranspiration, growing season length, and wintertime mountain glacier mass are all increasing. The key point with the glaciers is that there is more snowfall resulting in more wintertime mass accumulation – another indication of intensification.

    “This intensification has been proposed and would logically seem to result in more flooding and more intense tropical storm seasons. But over the observational period, those effects are just not borne out by the data in a consistent way,” said Huntington.

    Huntington notes that the long term and global scale of this study could accommodate significant variability, for example, the last two Atlantic hurricane seasons.

    “We are talking about two possible overall responses to global climate warming: first an intensification of the water cycle being manifested by more moisture in the air, more precipitation, more runoff, more evapotranspiration, which we do see in this study; and second, the potential effects of the intensification that would include more flooding and more tropical storms which we don’t see in this study,” said Huntington.

    The press release was to inform us that the paper was being published in the Journal of Hydrology….

    Journal of Hydrology, Volume 319, Issues 1-4 , 15 March 2006, Pages 83-95
    doi:10.1016/j.jhydrol.2005.07.003 opyright © 2005 Elsevier Ltd All rights reserved.

    Evidence for intensification of the global water cycle: Review and synthesis
    Thomas G. Huntington,
    US Geological Survey, 196 Whitten Rd, Augusta, ME 04330, USA

    Received 9 February 2004; revised 24 June 2005; accepted 7 July 2005. Available online 22 August 2005.

    Abstract
    “One of the more important questions in hydrology is: if the climate warms in the future, will there be an intensification of the water cycle and, if so, the nature of that intensification? There is considerable interest in this question because an intensification of the water cycle may lead to changes in water-resource availability, an increase in the frequency and intensity of tropical storms, floods, and droughts, and an amplification of warming through the water vapor feedback. Empirical evidence for ongoing intensification of the water cycle would provide additional support for the theoretical framework that links intensification with warming. This paper briefly reviews the current state of science regarding historical trends in hydrologic variables, including precipitation, runoff, tropospheric water vapor, soil moisture, glacier mass balance, evaporation, evapotranspiration, and growing season length. Data are often incomplete in spatial and temporal domains and regional analyses are variable and sometimes contradictory; however, the weight of evidence indicates an ongoing intensification of the water cycle. In contrast to these trends, the empirical evidence to date does not
    consistently support an increase in the frequency or intensity of tropical storms and floods.”

    The USGS press release comes after studies by Emanuel, Webster and Curry as if in an attempt at rebuttal, considering the timing and language of the notification.

    But the study was received by the Journal of Hydrology
    9 February 2004.

    [dubious comment deleted – moderator]

    [Response: Since this is a literature review only up to the end of 2003, it can’t be a rebuttal of the most recent work. – gavin]

    Comment by Tim Jones — 20 Mar 2006 @ 8:57 PM

  5. Re Tim:
    ‘over the past century’?
    I was under the impression that only for the Atlantic was there reliable tropical cyclone data prior to about 1943. Even studies confined to the Atlantic often ignore all data prior 1950, on the grounds that it is unreliable. Was their study specific to the Atlantic?

    Comment by llewelly — 20 Mar 2006 @ 9:09 PM

  6. Jae, those links given above are — as described — links to articles that include a quote from someone in the “dissenting camp” — read down in the article and you’ll find the quotes.

    Comment by Hank Roberts — 20 Mar 2006 @ 9:13 PM

  7. I’ve been living out in the Atlantic Ocean for the last 30 years, looking at these storms up close and personal. You’ll just have to take me on my word that ‘the ducks are in a row’. For someone like me who’s on the water all summer long, correlating hurricane intensity with rising sea surface temperatures is just about as easy as someone living on the snowline in the upper midwest for the last 30 years correlating the latitude of the winter snowline with global warming.

    It’s a no brainer.

    Comment by Thomas Lee Elifritz — 20 Mar 2006 @ 10:18 PM

  8. From the abstract:
    > ” … the observed weekly averaged SST from the 1º latitude x 1º longitude grid cell that
    > contained the storm’s center, during the hurricane seasons of 1982 through 2004….

    I wish they’d included — if such detail exists — some info on tracking the sea surface temperature _after_ a storm passed as well as the ‘before’ temperature. I recall mention that Katrina was unusual because while crossing the Gulf “Ring Current” the deeper water pulled up by the hurricane was almost as warm as the sea surface, so the deeper water fed almost as much heat energy into the storm as the surface. It could slow down, it could even have backtracked, without running out of warm water energy.

    Comment by Hank Roberts — 20 Mar 2006 @ 10:19 PM

  9. Re #3: Now those are some interesting authors, although I’m not sure who Davis is. M&K’s current article at TCS seems to be the expected attack on Hoyos et al. One point I would make is that the relationship between large hurricanes and SSTs as such will always be a little fuzzy since the presence of warm water at depth seems to pay a large role in storm intensification (as with Katrina when it crossed the Loop Current). This is because hurricanes churn up deeper water, so if that water is warm enough and the hurricane is moving slowly it can result in some rather abrupt strengthening. Since everyone still seems to be talking SSTs, I assume there must be a lack of data about temperature at depth.

    Comment by Steve Bloom — 20 Mar 2006 @ 10:37 PM

  10. Gavin wrote:

    [Response: Since this is a literature review only up to the end of 2003, it can’t be a rebuttal of the most recent work. – gavin]

    Certainly not.

    My point is that the USGS press release headline as well as the
    text did not indicate the literature review was only through 2003.

    “Century of Data Shows Intensification of Water Cycle but
    No Increase in Storms or Floods
    Released: 3/15/2006 12:13:21 PM”

    (excerpt)
    A review of the findings from more than 100 peer-reviewed studies shows that although many aspects of the global water cycle have intensified, including precipitation and evaporation, this trend has not consistently resulted in an increase in the frequency or intensity of tropical storms or floods over the past century. The USGS findings, which have implications on the effect of global climate change, are published today in the Journal of Hydrology.
    […]

    It was only after a lengthy search through the web that I found
    the page indicating the dates
    for submission to the Journal of Hydrology.

    I was misled, assuming that the USGS was revealing a preponderance
    of research to override the findings of Emanuel, Webster and Curry.

    Laymen readers did not know that the research was dated
    by more than two years. I would go so far, in light of the efforts
    of the current administration, the EPA, and of late even NASA
    to “manage” findings by climate scientists that someone intended
    for the press release from the USGS Newsroom to keep the public
    in the dark regarding this point as they proclaimed:
    “Century of Data Shows Intensification of Water Cycle but
    No Increase in Storms or Floods”

    [Response: Another problem with a “meta analysis” of this sort is that if you throw a lot of high quality work (like Emanuel’s paper or the Webster group papers) into the pot with a lot of junk, you’re bound to get an ambiguous view about what is going on. –raypierre]

    Comment by Tim Jones — 20 Mar 2006 @ 10:49 PM

  11. Some time ago, I pointed out that increased settlement on the Gulf coast and increased sea surface temperatures are independent of one another. Roger Pielke is asking the wrong question. It is not whether most of the increase in hurricane damage is from increased settlement. That is totally irrelevant unless you are planning to depopulate the area (putting on a tin foil hat and looking at the management of Katrina hmmm…) Whether there is an increase in hurricanes and/or their intensity is another issue.

    IF you believe that the increase in damage is from societal causes, then how much would it cost to clear the coast of houses? Could this be done at all? If it cannot be done, what mitigations are possible. How would the cost of decreasing anthropic global warming compare with the cost of moving people and industry from the Gulf coast of the US? Are there other things that could be done?

    Comment by Eli Rabett — 20 Mar 2006 @ 10:58 PM

  12. Re 11, Eli:

    If the public & policymakers get the impression that reducing GHG
    emissions will reduce US hurricane damage, but, after GHG emissions
    are dramatically reduced, US hurricane damage either remains stable or
    continues to rise, there will be a loss of trust among policymakers
    and members of the public.

    If current settlement trends continue, and a dramatic increase in
    hurricane preparedness does not occur, the fact that settlement trends
    are the dominant factor will mean that hurricane damages will most
    likely continue to increase even if GHG emissions are reduced to
    zero.

    The increase in hurricane damage due to increase in settlement
    does matter, because it means that the allowing people and
    policymakers to think GHGs are the only factor, would be a serious
    mistake. Reduction of GHGs needs to be advocated, but it should not be
    advocated on the basis that a reduction in US hurricane damages will
    necessarily follow.

    Reducing GHG emissions will have many benefits, but when it comes to
    hurricanes, such action can only hope to slow or halt the rise in
    intensity. This will not (by itself) reduce US hurricane damages; it
    will only prevent US hurricane damages from rising as fast as they
    would have if GHG emissions went on ‘as usual’.

    (Aside: ‘depopulation’ is hardly the only way to cope with settlement
    trends; for a society as wealthy as we are, preparedness – much, much
    more extensive preparedness – is another way.)

    (Second aside: As far as I know, only for the US have settlement
    trends been shown to be the dominant factor in tropical cyclone
    damages. This implies that AGW-induced increases in intensity play a
    larger role in a global context.)

    [Response:It’s perhaps ironical that the hutticane activityaffects the petroleum activity in the Gulf, which is associated with increased levels of CO2. These damages come on top of the coastal settlements. But, this is not our focus here, as we take a scientific view of tropical cyclones. The important question is: is the tropical cyclone pattern changing? Are the TCs becoming more frequent or intense? Rather than looking at insurance coasts, one could look at the rainfall associated with the storms, in addition to usual direct measurements. Since the storms are fuelled by the gas-to-liquid conversion of water, the associated rainfall amounts ought to provide a clue of the ‘fuel consumed by the hurricanes’. -rasmus]

    Comment by llewelly — 21 Mar 2006 @ 12:35 AM

  13. 8,9:

    I was at the talk, and I believe the question was raised about depth of warmth/heat content…and Davis acknowledged that it would be good information to have but it was not available for their study.

    BTW, Davis is one of the World Climate Report editors/contributors…In fact he must have written their recent bit on Ken Kunkel’s extreme weather presentation, because he was the only one from WCR there.

    Even more interesting, if the moderators allow this diversion, Davis very recently co-authored a paper with Real Climate’s very own Dr. Michael Mann (via their advisee, who was 1st author), and that paper won the AAG Climate Specialty Group’s paper of the year award. For those of you following the McIntyre-Mann, “x degrees of separation” game over at inkstain, I think this is a very interesting way of arriving at 4.

    Okay, diversion over. Sorry.

    Comment by Kenneth Blumenfeld — 21 Mar 2006 @ 2:35 AM

  14. llewelly, “snark on” I take it you are referring to the current high level of trust and mutual respect between those in the US engaged in climate science and those in the US who are making policy /snark

    However to return to serious, I think you are offering a false choice. The first question we must confront is whether increasing GHG concentrations are intensifying huricanes. The answer appear to be increasingly yes, and on the science policy side the debate is becoming increasingly strident. See for example Jerry Mahlman’s comment http://tinyurl.com/p89o2 for an extreme example of one side and almost any of Bill Gray’s comments on the other. The difference between what is occurring now and what has happened on climate issues in the past is that those on the consensus side have finally realized that it is necessary to push back against the denialists and their funders.

    The second question is what effect will that have on storm damage. It is there that one sees again the tension between AND and OR. The Pielkes and Lomborgs of the world would offer a choice of either one or the other, pick one. It looks increasingly likely that to do so would produce at best a leveling off of hurricane damage into the future. This is not to mention that Gray is probably right that there will be an increase in storm intensity and number over the next 15 or so years as part of a natural cycle, so the problem is really natural cycles AND GHG diriven sea surface warming AND settlement and investment on the Gulf and Atlantic coasts in the US. It is also worth restating that in coatal areas where there has not been such a massive change in settlement patterns, the anthropic and natural effects dominate. We clearly have to take actions on many levels, but you can ruminate on the morality of the following postion: Assuming that hurricane damage in the US is driven by settlement of the Gulf Coast, the US might make a policy choice to emphasize adaptation (the cost of resettlement would be astronomical (> 10^Kyoto). To do so without taking action on GHG emissions would leave the rest of the world (or at least those parts subject to tropical cyclones) with an increasing problem.

    Allow me to invert your question. What if we take actions on the coastal settlement side and things continue to get worse because of natural and anthropic sea surface warming? The real problem IMHO, is that politics operates by simplification to a single point while in the real world there are many factors that operate simultaneously. They can be addressed singly or in combination. The latter is more effective as it allows trade offs between actions. As far as the science part of it goes it is increasingly clear that GHG increases are increasing storm intensity. Nailing that down is the important thing that climate science must do at this point, so that we can move on to the policy issue of what to do about it (or not)

    Comment by Eli Rabett — 21 Mar 2006 @ 10:26 AM

  15. Re 13:

    Bob Davis also won the AAG Climate Specialty Group Paper of the Year award in 2004 for his paper “Decadal changes in summer mortality in U.S. cities,” International Journal of Biometeorology 47:166-175. On this instance his co-authors were Pat Michaels, Wendy Novicoff, and myself.

    Either Davis has an “in” with the Climate Specialty group, or he actually produces some decent stuff :^)

    -Chip

    Comment by Chip Knappenberger — 21 Mar 2006 @ 10:59 AM

  16. Gavin- A nice summary, thanks.

    11, 12, and 14: For some simple math on where policy makers have levers to address future hurricane impacts, please se this post:

    http://sciencepolicy.colorado.edu/prometheus/archives/disasters/000746forbidden_fruit_jus.html

    2, the world is seeing a rush to the coasts, and an increase in the wealth in exposed locations at rates in some places that far exceed that seen in the US. The human vulnerability is obviously much greater in developing countries

    Comment by Roger Pielke, Jr. — 21 Mar 2006 @ 11:32 AM

  17. Gavin-

    One further comment. You write, “This is odd, not because it’s not true (and is the principle reason why the attribution of more intense hurricanes to GW is not yet set in stone), but because Landsea has previously been much more of a champion of favoring observations over modelling.”

    I think this misses Landsea’s point, though I have seen others make the same critique of Landsea’s views, sometimes a bit too glibly.

    It is one thing to argue about models versus data in cases where the basic theory is commonly understood. We saw this occur in the satellite versus surface temperature trend debate in which at various times different sides of this debates aligned with models or data. Modelers generally support their models, empiricists the data, and in general Landsea seems to follow this tribal association as might be expected.

    However, it is something altogether different in a situation where the basic theoretical underpinning of the models is under question, as you suggest in this case, “possibly the theory needs work”.

    Landsea is not selectively picking models over data in this case, but saying very much the same thing that you seem to be saying — he is saying the recent studies in hurricane intensity trends, if they stand up, call into question the theoretical basis on which recent model studies are based (e.g., Knutson and Tuleya). He is not saying, as you seem to imply, that we should believe the models in this case, but that the data, if true (and clearly he thinks there are remaining problems with the data), go against the fundamental theoretical understandings on which data is interpreted and models are based. This is a case of data versus theory, not data versus model.

    Comment by Roger Pielke, Jr. — 21 Mar 2006 @ 12:08 PM

  18. Re Eli, 14:

    llewelly, “snark on” I take it you are referring to the current high
    level of trust and mutual respect between those in the US engaged in
    climate science and those in the US who are making policy /snark

    I agree that the unwarranted suspicion many US politicians have
    towards climate scientists is a serious problem – perhaps the most
    serious those of us in the US face. However, I believe a mistaken
    impression will surely worsen the situation.

    However to return to serious, I think you are offering a false
    choice.

    Unfortunately, I’m not sure what choice you think I offered. The
    statement about policy which I had intended to offer was: ‘Reduction
    of GHGs needs to be advocated, but it should not be advocated on the
    basis that a reduction in US hurricane damages will necessarily
    follow.’ If you got the impression that I was offering some kind of
    choice between resettlement and reduction of GHG emissions (as I think
    Roger appears to offer), I apologize for being unclear. While I agree
    with Roger Pielke, Jr. that settlement trends are the primary cause of
    increases in US hurricane damages, I do not agree that
    resettlement should be pursued ‘instead of’ reduction of GHG
    emissions. However much resettlement might reduce US hurricane
    damages, it will have little effect on many of the other dangers of
    AGW. (Such as changes in precipitation, and changes in growing season
    length.) Resettlement of US residents will also have no effect on
    tropical cyclone damages in the rest of the world. I believe that if
    resettlement is feasible, it can only play a partial role in a
    solution to US hurricane damages. I suspect we agree on these last few
    points.

    As for the rest of your post, I don’t yet have much to say, except to
    thank you for pointing me at your blog.

    Comment by llewelly — 21 Mar 2006 @ 1:16 PM

  19. We cannot forget another simple factor…the relationship between global warming (GW) and increasing hurricane damage due to incresasing storm surge.

    GW raises sea levels, mostly by thermal expansion. The higher the sea levels, the more damage most land-falling hurricanes will do with storm surge alone (unless it is in an ocean area where sea levels are not rising as much as others).

    Statistically, it is storm surge that does the most hurricane damage. This makes most land-falling hurricanes more damaging than 100 years ago, all other things being equal, no matter what is happening to maximum hurricane intensity.

    Secondly, land-falling hurricanes will most likely continue to do increasingly more damage in the next fifty years at least, all other things being equal, whether they are getting stronger or not due to greater GW-induced storm surge.

    As an aside, I am experiencing something that I never expected to see in my lifetime. Because of the special nature of my job and my wife’s businesses, I have in the last year personally met in Boulder Colorado, eight separate people (most with families), seven of them solidly middle class, who have left New Orleans, Florida and Texas, many voluntarily, some due to forced evacuation they say, due to hurricane experiences they have had.

    Comment by Richard Ordway — 21 Mar 2006 @ 2:00 PM

  20. 18, you have mis-stated my views. I do not offer GHG reduction and reducing vulnerability as “either/or,” but as an “and” —

    “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).”

    http://sciencepolicy.colorado.edu/admin/publication_files/resource-1766-2005.36.pdf

    [Response: This statement does seem to offer an AND, but I think maybe it is a different sort of AND than many people have in mind. My reading of this statement is that you are saying that the likelihood that global warming is increasing the destructive potential of hurricanes (and is likely to do so increasingly in the future) is irrelevant to the policy debate about hurricane damage. I read this as saying there’s plenty to be alarmed at when thinking about AGW, but hurricanes aren’t one of them. I don’t find that a tenable position (if that’s indeed what you’re saying) because the fact that the increase is detectable at all opens the possibility that hurricane strength will increase much more than models currently predict. In your BAMS article, you seem to draw comfort from the rather modest increase yielded by 3D mesoscale models, but are discounting the possibility that Emanuel’s observational analysis really is suggesting an intensification mechanism that isn’t yet understood. When you combine the possibility (if not probability) of severely intensified hurricanes in 2050 with the unlikelihood that coastal settlement patterns will change much, you do indeed get something related to AGW that needs to be factored into the mix. Nobody ever said that hurricanes are the main reason we should do something about AGW, but people are absolutely right to take hurricane effects as an example of the changes being wrought on the climate, and to be alarmed as a result. –raypierre]

    Comment by Roger Pielke Jr. — 21 Mar 2006 @ 2:01 PM

  21. Re Roger, 20:
    I appologize for mis-stating your views. Thank you for your clarification.

    Comment by llewelly — 21 Mar 2006 @ 2:17 PM

  22. Regarding posts 4 and 10 from Tim Jones regarding:
    Huntington, T. G. 2006, Evidence for intensification of the global water cycle: review and synthesis, Journal of Hydrology, 319:83-95.

    The chronology is important.

    Considering that my this paper that was formally published on March 13 2005 was submitted in February 2004 and was accepted in final form in July 2005, and considering that I am not clairvoyant, I don’t think I should be faulted for not having included the many papers published on this topic in 2005 and 2006. The lengthy delay in getting papers published at the Journal of Hydrology is simply out of my control and I do not think it is incumbent on the USGS to add a disclaimer on every press release that additional papers have been published since the acceptance of the paper that either support or are contrary to its findings.

    Note that it is simply incorrect to state that the compilation of papers extends only through 2003, if you look at the report you will see that there are 18 papers cited from 2004 and 5 papers cited from early 2005 (including Trenberth et al. that was cited as in Press at the time).

    If I were to submit this review today I would make certain changes to accommodate newly published research.

    In the paper I state that there is no evidence that storm frequency, intensity, or duration increased in the 20th century. However, since that paper was submitted in early 2004 and was “In Press”, more than a year ago, recent papers by Emanuel et al., 2005, Nature 436:686-688; Webster et al. 2005 Science 309:1844-1846, and Hoyos et al. 2006 (Released in March 2006 ScienceExpress) have emerged reporting trends of increases in storm intensity.

    With the benefit of these new reports, I wish I could have cited those recent papers for observations of trends, AND, by the way, I probably should have also cited (Landsea et al 1999; Climatic Change 42:89-129; Goldenberg et al., Science, 2001; 293:474-479, and Chan and Liu 2004 J. of Climate 17:4590-4602) for reporting lack of trends. And, now I would cite Pielke et al. 2005 BAMS Nov. 2005 pages 1571-1575 as a review of the issue that places these recent papers in context. In light of these recent papers I would change the language to state “the evidence does not consistently support an increase in the frequency or intensity of major storms”.

    To my mind the more important result of this review paper was in the synthesis of information from many discipines that point towards an ongoing intensification of the hydrologic cycle — not that I did not find evidence for more frequent or intense storms. I believe that hydrologic responses to cimate change other than “extreme events” have not received the attention that they should have either in the IPCC or other assessments, in part because of the attention directed towards “extreme events”. It is ironic, therefore, that the feedback that I have received on the J. Hydrol paper has been almost exclusively with the findings on “extreme events”.

    While on the topic of updating the paper with recent findings (for those interested in anything other than extreme events) I would add the following notes.

    If I were to publish this paper today I would also cite Milly et al. 2005 as a very recent global modelling study that supports the argument that the global water cycle has intensified.

    I would also include Schwartz et al. (2006) for further evidence of lengthening of the growing season and greater ET. I would also cite Phillipona et al. 2005 for further evidence of water vapor feedback. I would also cite Soden et al. (2005) for evidence of increasing water vapor in the upper troposphere, I would also cite Held and Soden (provided it is accepted for publication) (now submitted to the Journal of Climate) for findings consistent with increasing tropospheric water vapor. I would cite Kundzewicz et al. (2005) for lack of evidence for an increase in flooding. I would also cite Johannessen et al. (2005) for increase in winter precipitation over Greenland. I would also cite Zwally et al (2005) for evidence from the Greenland Ice Sheet and the East Antarctic Ice Sheet mass balances that are consistent with increasing winter precipitation and warmer temperatures.

    References Cited:

    Held, I.M., and B.J. Soden. Submitted. Robust responses of the hydrological cycle to global warming. Submitted to J. Clim. 2005

    Johannessen, O.M., K. Khvorostovsky, M.W. Miles, and L.P. Bobylev. 2005. Recent Ice-Sheet Growth in the Interior of Greenland. Science 310:1013 – 1016.

    Kundzewicz, Z.W., D. Graczyk, T. Maurer, I. Piskwar, M. Radziejewski, C. Svensson, and M. Szwed. 2005. Trend detection in river flow series: 1. Annual maximum flow. Hydrol. Sci. J. 50:797-810.

    Milly, P.C.D., K.A. Dunne, and A.V. Vecchia. 2005. Global pattern of trends in streamflow and water availability in a changing climate. Nature 438:347-.

    Philipona, R., B. Dürr, A. Ohmura, and C. Ruckstuhl. 2005. Anthropogenic greenhouse forcing and strong water vapor feedback increase temperature in Europe. Geophys. Res. Lett. 32:L19809, doi:10.1029/2005GL023624.

    Schwartz, M.d., R. Ahas, and A. Ahas. 2006. Onset of spring starting earlier across the Northern Hemisphere. Global Change Biol. 12:343-351.

    Soden, B.J., D.L. Jackson, V. Ramaswamy, M.D. Schwarzkopf, and X. Huang. 2005. The radiative signature of upper tropospheric moistening. Science 310:841 – 844.

    Trenberth, K.E., J. Fasullo, and L. Smith. 2005. Trends and variability in column-integrated atmospheric water vapor. Climate Dynamics 24:741-758.

    Zwally, H.J., M.B. Giovinetto, J. Li, H.G. Cornejo, M.A. Beckley, A.C. Brenner, J.L. Saba, and D. Yi. 2005. Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise: 1992-2002. Journal of Glaciology 51:509-527.

    [Response: Thanks for the comments. I share your frustration at what does and does not get picked up on, but I think you will find that the media (in general) are quite predictable. It is sometimes then possible to ‘head them off at the pass’ (so to speak) by crafting press releases with that in mind. -gavin]

    Comment by Tom Huntington — 21 Mar 2006 @ 3:35 PM

  23. Thank you, Tom Huntington!

    I would greatly prefer that RealClimate stick (mainly) to climate and avoid comment on policy matters, etc. Thank you all.

    Comment by David B. Benson — 21 Mar 2006 @ 3:50 PM

  24. If there is some way of quantifying the difference in damages between Cat 4 and Cat 5 events this could help make the financial case for GHG abatement. The long tapering off period doesn’t help though. A Queensland farmer said his crop was designed to resist strong winds but Cyclone Larry was too powerful. Governments seem to be wondering if they have to budget for emergency aid on a more regular basis. People are starting to join the dots.

    Comment by Johnno — 21 Mar 2006 @ 6:00 PM

  25. Thanks for the first hand insights into your paper. I am puzzled by the paradox that you observe an “ongoing intensification of the hydrologic cycle, but not an increase in storm frequency and intensity”. I cannot envision physically that the hydrologic cycle can intensify and there not be an increase in storm frequency and intensity of floods and droughts. The glacier mass balance record in alpine regions does indicate a steepening of the gradient. That is a greater difference from the terminus to the head of the glacier. However, there is not a consistent rise in alpine glacier winter balance to offset the increase in summer melting. Hence the increasingly negative glacier mass balance record that you are familar with.

    Comment by Mauri Pelto — 21 Mar 2006 @ 8:43 PM

  26. The hydrologic cycle can change because of changes in plant cover — it’s a common observation that after a forest fire or logging, streams and springs will flow higher and longer for a period of years. I recall hearing somewhere that removing invasive Eucalyptus species is having the same effect in areas of drought in Africa.

    I’d suspect that a change in soil microbiology might also change the way the soil holds onto water — and we know we’re getting changes due to increased deposition of nitrogen, for example, from the air. E.g.:
    http://bangor.ceh.ac.uk/terrestrial-umbrella/people.htm

    (Nitrogen is a big problem in native plant areas because it’s one of the limiting nutrients, and when it’s supplied whether by fertilizer or grazing animals or rainfall, that tips the balance toward European and Asian annual grasses that are very shallow-rooted — they steal every drop of rain that falls, and then burn by midsummer when the N. American native perennials are just setting seed; after a few years the deep-rooted perennials are gone; after a few more years so is the topsoil).

    That’s just an amateur’s recollection, but I am sure that the climatologists can get a lot of info from the soils scientists about various known ways that streamflow can be changing that are not directly outputs of changes in storm frequency or intensity. And of course the rates of change may be changing.

    Comment by Hank Roberts — 21 Mar 2006 @ 8:58 PM

  27. Re 25, Mauri Pelto:
    Storm frequency and intensity are noisy signals. Intensity is also difficult to measure. To get a rough idea of how noisy it can be, see http://www.aoml.noaa.gov/hrd/tcfaq/E11.html , which has an 1851 to 2004 record of tropical storm activity in the atlantic. (Note: the pre-1950 years in that list are of limited reliability.)

    Comment by llewelly — 21 Mar 2006 @ 9:32 PM

  28. Re #3

    I believe they sent the paper into GRL. It’s an interesting bit of work, but in many respects it is just as limited as the Kerry Emmanuel paper they criticized, just in the opposite direction. Emmanuel looked at basin averaged SSTs (err on large scale) and Davis et al looked at single gridpoint SSTs (err on small scale). Since hurricanes are probably pulling energy from the SSTs over a scale larger than Davis and smaller than Emmanuel, there is probably some information lost/obscured in both cases.

    Comment by Ben — 21 Mar 2006 @ 9:51 PM

  29. Ray- (response to 20)

    OK, I’ll bite. The handwaving is fine and good, but we can do better. Give me a quantitative estimate of the effects that GHG reductions can have on future hurricane impacts. Here is my framework for exactly this calculation:

    http://sciencepolicy.colorado.edu/prometheus/archives/disasters/000746forbidden_fruit_jus.html

    Give me a scientific basis for understanding what role you think GHG reduction policies should play in hurricane disaster mitigation. I get lots of criticism of my work, but the critics never offer any alternative analyses, so here is your chance ;-)

    Thanks.

    [Response: Your paper sets up a false dichotomy regarding controlling hurricane damage by vulnerability control vs controlling hurricane damage by GHG reductions. It presupposes that one is faced with a decision between controlling GHG just for the sake of hurricanes, and forgetting about GHG’s and spending money on bribing people to live further from the shoreline. (In your 2000 paper, you seem to make this point more broadly; you state explicitly that you think that climate impacts are best addressed through adaptation rather than prevention. I’m not saying that’s a defensible position based on your analysis, but that is indeed what you state, begging the question of why you go on to imply that it’s worthwhile to control GHG anyway). In reality, the decision is not at all like your false dichotomy. GHG’s have many impacts, increased hurricane damages being one among many. So, your comparison of the climate-related component of increased hurricane damages to the vulnerability component is irrelevant, since nobody is talking about controlling GHG’s for the sole purpose of reducing hurricane damages. Seen in this light, the public attention to the Emanuel and Webster papers is not at all misplaced. It’s part of the whole spectrum of GHG effects that need to go into the assessment of the nature of the threat. To be sure, hurricane damage has high “availability” as a threat, since people can picture it more easily than extinction of some invisible mycorhyzae, but that doesn’t make it irrelevant — it just means that some other threats are under-appreciated. For that matter, it wouldn’t take much tweaking of your “high end” climate damage numbers to make the costs look more alarming: what if the damage function turns out to be quadratic rather than linear? What if Emanuel’s observations turn out to mean that the effect of SST on hurricane intensity is larger than the theoretical prediction? What if we recognize that under business as usual CO2 won’t stop at a doubling, but go on eventually to a quadrupling or worse? None of this says that one should neglect spending on reducing vulnerability, but the clear message I take away from your writing is that people should just calm down and forget all about the effect of AGW on hurricanes. Why wouldn’t people care about such a massive sign of human impact on nature? By the way, in your arithmetic example at the above link the damages are all monetized. Could you clarify how loss of life is figured into these numbers? You make a 10% increase in hurricane damage look small compared to the increase in monetary damage due to economic factors, but comparing a 10% increase in lives lost (as an example) with a 100% increase in costs of McMansions on the shoreline floating away on the flood is not necessarily appropriate. –raypierre]

    Comment by Roger Pielke Jr. — 21 Mar 2006 @ 10:15 PM

  30. Re 28, Ben:
    In addition to the concerns you list, intense hurricanes normally cause some upwelling of deeper waters, and if they are slow-moving, thus somewhat dependent on the temperature of deeper waters.

    Comment by llewelly — 21 Mar 2006 @ 10:22 PM

  31. Re 22. “Evidence for intensification of the global water cycle: review and synthesis, Journal of Hydrology,” …

    The title at the USGS site is: “Century of Data Shows Intensification of Water Cycle but No Increase in Storms or Floods”
    http://www.usgs.gov/newsroom/article.asp?ID=1475

    Who made the decision to change the title to include “but No Increase in Storms or Floods”?

    My career (1976-2005) was hydrologic modeling and flood prediction for the Midwest and Great Plains. I was with NWS Kansas City River Forecast Center from 1976-1979, then and moved to Minnesota to help start up NWS North Central River Forecast Center. The summer “Great Flood of 1993″ in the Mississippi River basin went on for three months. Other very large floods in the Midwest were in 1997 and 2001. Runoff into Devils Lake in North Dakota has been excessive since 1995.

    I understand that the Midwest is not the world, but from what I’ve seen happening in the Midwest and many other places throughout the world it seems to me to be counter to your conclusion of No Increase in Floods. Unfortunately, I have not read more than the press release about your work. I should add too that I was not allowed at work to study or talk about trends in frequency and magnitude of floods or trends in temperatures and precipitation, due to the “highly political and controversial subject of global warming”. I encountered “great difficulties” from Jan of 2000 until July of 2005 as a result of my concerns with climate change effects on hydrologic modeling and flood prediction. I removed as a federal employee in July of 2005 for objecting to not be able to study or talk about climate and hydrologic change while at the office.

    Did you encounter obstacles or “firm suggestions” in coming up with and doing your study and report? If so, could you share them with us?

    Comment by pat neuman — 21 Mar 2006 @ 11:26 PM

  32. A post I submitted at the URL referenced in #29:

    “You said:

    ‘But lets be slightly more realistic, how about Kyoto? Assuming that the effects of GHG reductions on hurricane intensity are instantaneous and exactly proportional to emissions concentrations (also dubious assumptions, but lets go with them) under full and successful implementation of Kyoto, including the participation of the US, the reduction in projected damages would be about $0.03.’

    Three cents on the dollar doesn’t sound like a lot. However, multiply this by a billion in the case of such a hurricane (i.e. the hurricane causes a billion dollars in damage) and you get 30 million dollars.

    Take an average number of storms (6) in a given year, with, say an average of 50 million dollars in damage. There’s 300 million dollars in damage, which could bave been roughly 10 million dollars cheaper from which to rebuild.

    Try increasing the savings from hurricane damage in the future with every ppm of CO2 that is reduced on a yearly basis. Billions of dollars will be saved! Now that sounds like a lot, eh?”

    [Response: And also factor in that reduction in hurricane damage is not the only, or even the major, benefit of GHG control, and perhaps also the fact that it’s not entirely clear that a smart implementation of Kyoto would actually “cost” anything, given ancillary benefits of energy efficiency and health benefits from reduced or cleaner coal burning. –raypierre]

    Comment by Stephen Berg — 22 Mar 2006 @ 1:17 AM

  33. Scientists debate whether natural causes or AGW is responsible for increasing hurricane intensity.

    Some people advocate reversing the trend toward increasing coastal development while others urge that protective measures should be taken.

    Policymakers say that they need more evidence before they take action.

    Meanwhile, Nature may provide the answers.

    Comment by Henry Molvar — 22 Mar 2006 @ 2:14 AM

  34. Re: #33, “Policymakers say that they need more evidence before they take action.

    Meanwhile, Nature may provide the answers.”

    Richard Clarke’s testimony at the 9-11 Commission hearings had one stunning but accurate statement. It goes something like this:

    “It takes bodybags before something is done about a certain problem.”

    I just hope it won’t end up in the millions before significant action is taken to combat this urgent problem.

    Comment by Stephen Berg — 22 Mar 2006 @ 2:53 AM

  35. Gavin’s post is a good one, especially ending on the note of there being problems with theory. As far as that goes, I find it interesting to note that in the wake of TC Larry, Australia’s CSIRO is apparently projecting stronger storms but also *fewer* of them in the future.

    http://www.theage.com.au/news/national/mother-nature-to-pack-a-meaner-punch-in-future/2006/03/21/1142703358070.html

    Furthermore, this is consistent with a recent modeling study out of Japan, except that the Japanese study projects an anomalous frequency *increase* in the Atlantic even though frequencies elsewhere go down:

    http://kyousei.aesto.or.jp/~k041open/ipcc_ar4/kouchi/final_Nov15-oouchi_etal2005_JMSJ.pdf

    I have written up a blog post about this question of whether GW could cause stronger storms but less of them, except for in the Atlantic, but I’m no scientist. I’m just going on what I hear. Would be great if the minds at Real Climate could weigh in on the matter.

    http://scienceblogs.com/intersection/2006/03/stronger_storms_less_frequentl.php

    Comment by Chris Mooney — 22 Mar 2006 @ 3:32 AM

  36. From a strictly non-policy oriented point of view, using hurricanes to ID a global warming trend is a bit like using dinosaur fossils to determine the Cretaceous-Triassic geological boundary. Hurricanes are big, relatively rare, but of great interest to the general public – like dinosaurs. There are certainly better indicators of global warming trends – ice sheet volume, sea ice extent and sea surface temperatures all come to mind – but hurricanes get people’s attention.

    From a media point of view, the most irritating mis-statement I’ve seen is “Scientists state that no single event can be determined to be due to global warming.” This was at the end of a news article, and gives a misleading impression. A rather different way to say this would be “No single event can be seen as definitive proof of global warming – rather, a trend or pattern must be identified by analyzing a large number of individual events.” The fact that hurricane events are relatively rare leads to a limitation in the amount of data available – fewer events, and that’s why the ‘skeptics’ have to rely on statistical rather then mechanical arguments (notice also that the media seems to avoid any mention of the fact that hurricanes operate as ‘heat engines’).

    Another statement that seems unsupported is “the natural cycle of hurricane activity is increasing”. It would be okay if it was just “hurricane activity is increasing”. This ‘natural cycle’ is based on what data?
    1999 time series analysis paper is one citation, but this kind of time series analysis seems highly questionable, at least. Correlation with sunspot activity? They also say that “Time series analysis offers a rigorous approach for extracting underlying cycles in a set of observations” – interpretation: it’s a bit better then eyeballing a chart – but look: fancy math! Furthermore, this paper deals with hurricane frequencies – which are supposedly? unrelated to SSTs. In any case, the idea that there is a ‘natural cycle’ of hurricane activity that is increasing due to ‘global oscillations’ seems unsupported.

    Finally, the physics of a hurricane system is complicated, but takes place within the larger atmosphere-ocean system. What I’d like to know is specifically why hurricane intensity and frequency wouldn’t both be expected to increase, given that the SSTs play a primary role in hurricanes? Taking a look back at the Katrina ‘event’, if the hurricane hadn’t encountered a tounge of warm water in the Gulf (perhaps a separate ‘event’) it wouldn’t have amplified as it did. The depth of this warm layer was also critical – not just an SST effect. In the progression of tropical disturbance > tropical storm > hurricane the available energy is limiting the growth of the system; unless the vertical structure of the hurricane engine is blown apart by winds, the thing will grow when it hits a warm deep water zone.

    The media has done a very poor job of reporting on this issue. The reports are dominated by the phrase ‘experts say’ and little actual explanation is attempted. Painfully obvious is how it all seems.

    Comment by Ike Solem — 22 Mar 2006 @ 3:59 AM

  37. >Cretaceous-Triassic geological boundary.

    What have you done to the Jurassic!?

    [Response: Indeed. I am assuming that the reference is really to the Cretaceous-Teritary (KT) boundary – the K comes from the German spelling – gavin]

    Comment by C. W. Magee — 22 Mar 2006 @ 5:51 AM

  38. Chris, #35 — note the Japanese model you quote says increasing storms in the _North_ Atlantic. That would seem consistent with the heat transport and warmer sea surface temperatures — are they saying the Atlantic hurricanes will last longer as they go farther north in a warmer environment, so ‘more storm in the North Atlantic’ is explained?

    Comment by Hank Roberts — 22 Mar 2006 @ 7:20 AM

  39. Re SBerg (34). You need a convincing case to justify actions that will cost billions – that will potentially be diverted from causes for which there is zero doubt. The war in Iraq is an example of a decision based more on policy than evidence, which resulted in many bodybags on all sides. Many of us who were skeptical of the evidence for WMD at the time (and ridiculed for it) have since been proven correct. (Off-topic? I’m not the first to make a comparison to war/terror).

    A decision to act on AGW theory/evidence (take your pick) is not without risk, as many seem to assume.

    Comment by PHEaston — 22 Mar 2006 @ 8:04 AM

  40. The evidence of coastal property prices is mixed here in the U.S.

    This is still the norm:
    Real Estate report

    “A waterfront property is worth from 8 percent more (on the Gulf) to 45 percent more (around the Great Lakes) than a comparable inland site. ”

    But I read of real estate being abaondoned along the gulf coast in regions. I start to see a few examples of California beach property being abandoned.

    One more severe storm season and prices should start to drop dramatically.

    Comment by Matt — 22 Mar 2006 @ 8:52 AM

  41. Hank, # 38–

    Yes, North Atlantic. Normally just saying “Atlantic” would be enough, but of course, there are also predictions that global warming will bring hurricanes to the South Atlantic:
    http://scienceblogs.com/intersection/2006/03/introducing_tropical_cyclone_l.php

    So thanks for catching me on that.

    Perusing the Japan study I cited, the answer to your question is this:

    “A comparison between the future and present-day experiments reveals that the occurrence number in the future experiment is generally reduced, showing approximately 30% total global reduction, as stated before. The reduction trend remains evident across the Northern Hemisphere, Southern Hemisphere, North Indian Ocean, western North Pacific, South Indian Ocean, and South Pacific, at the 99% level of statistical significance (based on the twosided Student’s t-test). On the other hand, a tendency of increase in the future experiment is found in the North Atlantic Ocean, where the occurrence number increases by about 30%. Though the reason for this contrast in the tendency is not presently clear, a clue may be obtained by investigating the change in the sea surface temperature (SST) between the two experiments….We can see that a positive region of SST spreads over the southeastern part of the North Atlantic Ocean. The region approximately corresponds to the area of generation for most of the hurricanes that approach and threaten the eastern coast of the United States. Of the several signatures of such warm tongues over the globe, the one over the North Atlantic is conspicuous in size, and, more importantly, coincides with the tropical cyclone source. In addition, the accompanied difference in the rainfall amount, which is shown in the lower panel of Fig. 3, exhibits a trend of increase, indicative of activated convection. This should help “seed” the tropical cyclone generations. These features can be responsible for the increased frequency of tropical cyclones over the North Atlantic Ocean.”

    Again, the study is here:
    http://kyousei.aesto.or.jp/~k041open/ipcc_ar4/kouchi/final_Nov15-oouchi_etal2005_JMSJ.pdf

    Comment by Chris Mooney — 22 Mar 2006 @ 9:26 AM

  42. Re 3:

    Our paper has been submitted to GRL and is still in the review process.

    Our basic conclusions are that:

    1) Encountering a SST of about 28.25C is necessary for an Atlantic tropical cyclone in order to become a Cat 3, 4, or 5 storm.

    2) however, encountering SSTs greater than 28.25C doesn’t lead to stronger storms (i.e. there is no significant relationship between SST and intensity at SSTs above 28.25)

    So, rising SSTs will lead to a greater number of major hurricanes (up until SSTs rise enough that all storms encounter 28.25), but not stronger major hurricanes.

    This result is similar to that which is reported in Webster et al. (2005), where they find: “This increase in category 4 and 5 hurricanes has not been accompanied by an increase in the actual intensity of the most intense hurricanes. The maximum instensity has remained remarkably static over the past 35 years.”

    Further, we found the SST increases alone since 1982 (the start of the high resolution SST data) cannot explain all of the increase in the number of major hurricanes. Thus we conclude that other factors have also contributed to the observed frequency increase–a result that is supported by the results of Hoyos et al. (2006), at least for the North Atlantic.

    I am hopeful that our paper will be accepted at GRL and then look forward to a discussion of it on this group.

    I have some further thoughts on the implications of Hoyos et al. that I hope to share with you all–and to hear your thoughts on them.

    -Chip

    Comment by Chip Knappenberger — 22 Mar 2006 @ 11:20 AM

  43. >41 – Ah. Chris, I was actually thinking (probably NOT in line with proper use of the words) ‘North’ vs. the near-equatorial Atlantic. I expect you’ve got the naming of the Atlantic correct. I’ll wait on the experts to clarify the mechanism(s) if they have them to suggest.

    Comment by Hank Roberts — 22 Mar 2006 @ 11:46 AM

  44. Oops, yes, thank you, the KT boundary is the Cretaceous-Tertiary boundary not the Triassic. I was trying to refer to the large extinction event that occurred some 65 million years ago; if you wanted to date the event using the sedimentary record it would be better to look at a widespread, well-preserved fossil type – a marine snail or something – rather then dinosaurs. The extinction of the dinosaurs (and a host of other species) is now generally blamed on meteor strike-induced climate change.

    Dinosaurs link up to the current situation in other ways; some deceased swamp dinosaur carbon is probably going up a coal-fired power plant smokestack right this very moment. Yes, coal – the highest carbon output per energy unit of all the fossil fuels, and the source of 86% of electricity-related CO2 emissions in the US. Readers might want to look here for the EIA 2003 report: 2003 CO2 emissions

    Comment by Ike Solem — 22 Mar 2006 @ 2:09 PM

  45. Ike, I thought the majority of the world’s minable coal reserves were laid down during the Carboniferous? Probably some coal was laid down during the Cretaceous, but given the Cretaceous had much lower carbon levels than the Carboniferous, I suspect much less. (Here I’m assuming more CO2 in the atmosphere means more carbon in the biosphere – is that reasonable?)

    Comment by llewelly — 22 Mar 2006 @ 3:11 PM

  46. Re #42: Er, Chip, didn’t you guys already draw your conclusions regarding Hoyos et al? From the conclusion of the recent WCR/TCS article:

    “SSTs have been increasing since 1970, as have major hurricanes, but the connection is not nearly as simple as some authors are suggesting. And careful scrutiny of ALL of the available data shows the connection to global warming is less than tenuous.”

    To all appearances, this statement even contradicts your own recent paper. What’s up with that?

    Comment by Steve Bloom — 22 Mar 2006 @ 3:22 PM

  47. As early as 1992 my Earth Day display on GW had a big hurricane on it, with mention of GW contributing to hurricane intensity AND frequency. I’m not gloating that I was right — I wish I had been proved wrong.

    RE FREQUENCY. Some people have suggested that if SST (& GW) is increasing hurricane intensity, it seems logical it would also be increasing hurricane frequency (all other things being equal – which I suppose they may not be), since the storms are moving up in category: 1 to 2, 2 to 3, etc., then some “tropical storms” would also be moving up to Cat. 1, thereby increasing hurricane frequency.

    I thought of some way in which you could get more intensity, without increased frequency: Perhaps hurricanes & tropical storms are clubbing together into more intense storms (what would have been 2 hurricanes given lower SST, become 1 more intense hurricane, given the higher SST).

    OTOH, it might just be that there aren’t enough numbers to reach .05 significance on frequency, not that we can say for certain (at .05 sig) that frequency is NOT increasing. In other words, frequency might be increasing, but our statistical operations are what’s failing to tell us that (due to low sample number, not lack of association).

    Comment by Lynn Vincentnathan — 22 Mar 2006 @ 3:48 PM

  48. WRT 42. Based on a relatively recent EOS article setting forth the idea that it is not only SST but also the depth profile of the warming that effects hurricane strengthening in the Gulf, would it not be possible that additions Carribean heat content could warm the sea lower down, increasing intensity.

    [Response:I think that both high SST and that high temperatures need to extend some distance downward are requisites for hurricanes. The SST can be viewed as important for the instant processes, whereas the upper surface layer heat capacity determines what will be the subsequent SSTs. Hurricanes stirr up the sea (mixing or Ekman pumping), and if there is a thin warm surface layer, colder water underneath will be brought up, and hence give rise to lower surface temperatures (SST). There is also rain associated with hurricanes, falling over the local area, but I have not seen much discussion on how the rain water may affect SST/surface layer heat content – it’s probably not very important. The vertical temperature profile may also play a role, as warmer water is lighter, and thus the stability of the water column depends on how fast the temperature drops with depth – more stable water column is less prone to mixing. For the Ekman pumping (one good example of the Ekman pumping is the so-called ‘cold tongue’ near in the eastern part of the Pacific near the Equator), the stability is not so important, but rather the depth of the upper warm surface layer. Addition of heat content could result in higher temperatures deeper down, but this depends on the process. Warming from above, such as solar heating, depends on the penetration of the radiation. The lighter warm water tends to stay near the surface and sensible heat conduction plays little role (as opposed to advection, which is heat transport due to fluid motion). Over time, however, the heat may diffuse downward. Often the depth of the warm upper surface layers is influenced by ocean dynamics, meaning long and slow waves which are seen as slow undulation of the interface between the upper and deeper layers. These (Rossby) waves are also related to currents, because they set up pressure differences (geostrophic motion). It is believed that such waves play a key role in initiating and terminating El Nino events. I suppose it’s fair to say that the issue regarding SST and heat content is fairly complicated. -rasmus]

    Comment by Eli Rabett — 22 Mar 2006 @ 3:54 PM

  49. Does all of this really matter? AGW is happening and mitigation activities are needed regardless of what is going on with hurricanes. Shades of the hockey stick!

    Every intuition tells me that GW should affect hurricanes. However, my intuition is not science. I am concerned with the possibility that some of the very excellent scientists on this site may have foregone their science and succumbed to a similar intuition.

    I would assume that NOAA is at least mainstream, if not authoritative. A four month old article in their magazine states, “… the tropical multi-decadal signal is causing the increased Atlantic hurricane activity since 1965, and is not related to global warming”. Then come tongue in cheek papers by a couple of researchers who state that GW may affect intensity if not quantity. But another researcher reports in this thread (#42) that his work may refute that. All of this is early work and certainly should not throw over all of the work performed that lead to the NOAA conclusion.

    Yet here I read that that scientists such as Landsea and Gray, who belong to the NOAA viewpoint, are “dissenters”. Is dissenter the same as skeptic or denier? Are you not turning things on their head? Who is the “mainstream” voicing “accepted” science and who is the dissenter?

    I would appreciate having this clarified. I would not like to see the capable scientists on this site making themselves vulnerable to the same characterization currently reserved for AGW skeptics. The risk to reputations among those in the non-scientific aspect of AGW is not worth it, particularly on a topic that does not matter. Is it intuition or solid science that is speaking?

    [Response: There is a lot of debate on this issue, and definitive statements one way or the other are (at present) unsupportable. The NOAA ‘official’ claim of no GW influence was in many people’s opinion too definitive a conclusion and, in fact, NOAA has since modified its public stance to acknowledge the debate even within the agency. This is actually a good example of genuine disagreements on valid issues (for the most part) which contrasts markedly with the manufactured ‘controversies’ that keep coming up from the various contrarians. In this issue there is no real ‘mainstream’ – unless you consider ‘undecided’ a position – though some individuals have made clear their preferences for the interpretation. – gavin]

    Comment by Paul Dougherty — 22 Mar 2006 @ 3:56 PM

  50. Re #46:

    Steve: I think the results from Hoyos et al. fit nicely with our GRL results–SSTs are only part of the equation (at least in the North Atlantic–and neither paper makes it clear that anthropogenic effects are the primary cause of the warming of Atlantic SSTs during the past few decades.

    Re: #48: We didn’t incorporate any ocean data other than SST in our analysis, so I can’t really comment on the effects of a warming at depth. I am not familar with the EOS article, so I’ll have to look into it. Thanks for bringing to my attention.

    -Chip

    Comment by Chip Knappenberger — 22 Mar 2006 @ 5:34 PM

  51. Re #48 comment: Rasmus, farther up in the comments someone had the idea of measuring SSTs in the wake of cyclones as well as in their path. From your more detailed description of the dynamics, that sounds as if it might be somewhat helpful (although still not quite a replacement for a depth profile of heat content). Is anyone looking at such an approach?

    Comment by Steve Bloom — 22 Mar 2006 @ 7:05 PM

  52. Measuring SSTs in the wake is mentioned “farther up” at #8, #9 and #13

    Comment by Hank Roberts — 22 Mar 2006 @ 7:36 PM

  53. In response to Pat Neuman and Tom Huntington:

    As Tom probably knows, climatologists studying extreme rainfall use techniques that make it almost impossible to tease out meaningful temporal trends in extreme precipitation (and resulting local/regional flooding). Extreme rainfall, on an event-level is driven by the prevailing meteorological conditions…deep moisture, weak upper level winds etc. One could argue pretty effectively that a 100-year type storm requires a very special set of rarely-occurring conditions, and that even in the face of strong AGW, the change in probablility of one of these storms at any point is going to be so small that it will be almost immeasurable…How would you know, for example, that the probablility of such a storm has increased from .01 annually to .02 anually (a huge increase)? You can’t yet, since these probabilities are estimated from observed data, rather than changes in important meteorological factors, like precipitable water.

    Furthermore, analyses of extreme rainfall have been constrained by two important factors: the spatial dimension–that is, not enough gauges to measure the true rainfall maxima for most events–and also selection criteria–how many events are analyzed.

    In any case, I would argue that the methods used for extreme rainfall frequency analyses cannot actually answer the questions about temporal changes in local storm frequency, intensity, spatial coverage and seasonality. So it does not surprise me that the literature has not yet uncovered any significant changes…that is not really what folks have been looking for.

    Comment by Kenneth Blumenfeld — 22 Mar 2006 @ 7:56 PM

  54. Something I’d be grateful to see clarified is the impact on sea-temperatures at depth of the recently reported 30% decline in the Gulf Stream’s warming northward flow.

    Can anyone say whether a corresponding lack of cooling flow southward yet show identifiable effects on ‘STADs’, and if so, where ?

    regards,

    Lewis

    Comment by Lewis Cleverdon — 22 Mar 2006 @ 8:28 PM

  55. Re: 51

    Steve,

    What do you want to know about the pre- and post-storm SSTs? I have the weekly average SSTs in 1×1 lat/lon grids for weeks prior to the storm arrival, the week that the storm was there, and the week after it departed (for every 6-hr storm position from 1982-2005). In our paper, we use the SSTs in the week prior to the arrival of the storm in order to avoid the storm mixing problems. There is a clear difference between pre- and post-storm SSTs. Do you want to know the average difference by year, by storm, by region? I’d be glad to tally those things–given that I can find the time, and someone thought this would be a useful exercise.

    -Chip

    Comment by Chip Knappenberger — 22 Mar 2006 @ 9:23 PM

  56. re 53

    I think this is a good summary of the Great Flood of 1993 (not statistical). “The Great Flood of 1993 on the Upper Mississippi River â?? 10 Years Later”, 4 pages.
    http://il.water.usgs.gov/hot/Great_Flood_of_1993.pdf

    Statistics and historical flood data can be found through this link.
    http://waterdata.usgs.gov/mo/nwis/current/?type=flow#Ice_affected

    Comment by pat neuman — 22 Mar 2006 @ 9:54 PM

  57. re 50. … EOS article, so I’ll have to look into it … -Chip

    I think this is the EOS article (as mentioned in 50.)

    > Satellite Altimetry and the Intensification of Hurricane Katrina
    >
    > Eos, Vol. 86, No. 40,
    > News 4 October 2005
    > PAGE 366


    > Instead, Katrina intensified most rapidly
    > when she was over areas of anomalously high
    > dynamic topography, as measured by altim-
    > eters (Figure 2b). Katrina intensified first over
    > a warm-core eddy east of Florida as she grew
    > from a tropical depression to a Category 1
    > hurricane.Then, over the Loop Current and a
    > warm-core ring in the Gulf of Mexico, she inten-
    > sified from Category 1 to Category 5.
    >
    > These dynamic topography highs are a proxy
    > for the vertically integrated heat content within
    > the water column.The depth of the warm water
    > pool, and not merely the temperature at the
    > surface, provides the reservoir of energy to
    > intensify a storm [Shay et al.,2000].

    The above text was copied from a post (Oct 4, 2005) at:
    http://groups.yahoo.com/group/ClimateArchive/message/2291

    Comment by pat neuman — 22 Mar 2006 @ 11:11 PM

  58. Excerpts:
    Judith Currea: … “frightening prospect” …
    Jim Acosta: … “government hurricane forecasters have heard these dire warmings before and they’re not impressed” …
    Max Mayfield: … “natural variability ALONE is what this can be attributed to” …
    CBS Video, aired March 20: CBS Evening News with Bob Schieffer
    Superstorms And Global Warming, Jim Acosta (CBS) at:
    http://www.cbsnews.com/sections/i_video/main500251.shtml?id=1424013n

    Also, FYI:
    MR. MAX MAYFIELD, DIRECTOR. TROPICAL PREDICTION CENTER/NATIONAL HURRICANE CENTER. NATIONAL WEATHER SERVICE. NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION …
    Sep 20, 2005
    http://www.legislative.noaa.gov/Testimony/mayfieldfinal092005.pdf

    Comment by pat neuman — 22 Mar 2006 @ 11:52 PM

  59. There are several posts about hurricanes and their effect on SSTs. I found this paper on hurricane Edouard useful for understanding the basics, although a bit old (1997). I searched google scholar with ‘SST hurricane wake’ and got a number of similar studies.

    Vaguely related, this page has computer-modeling results that forecast SSTs, and potential ocean temperatures down to 3000m deep. Currents, salinities, and other modeled ocean properties are also available. I gather that there are relatively few direct measurements of ocean temperature profiles, but there are reasonably successful efforts extrapolating ocean temperature depth profiles using computer models. Of course this is all intended for use in real-time forecasting, not long-term trend analysis, or climate change studies, but I believe the underlying model is more flexible, although I don’t know. (I *do* know that plenty of other models intended primarily for short-term forecasting have been successfully used in climate change studies; see for exampleTom Knutson’s papers ). hycom.org has more information about the model.

    Comment by llewelly — 23 Mar 2006 @ 12:03 AM

  60. Pat Neuman in #57 has the correct cite for the EOS article I was remembering. Thanks

    Comment by Eli Rabett — 23 Mar 2006 @ 1:28 AM

  61. #58 Pat thanks for the link to the testimony. Dr. Mayfield is unequivocal in his emphasis that it is not global warming that is causing the higher activity. This strikes me as an unusually emphatic response if solely from a scientific viewpoint. The debate that is ongoing reminds me of the debates around global warming when I first attended a science conference on it in 1981, the details all fuzzy due to the complicated world, but the underlying physics clear as can be. The higher sst-hurricane relationship is the same providing an undeniable clear physical mechanism for enhancing hurricane development, but associated with many other variables that make is difficult to pin down the exact impacts that have and will occur from higher sst. This makes NHC stand on the sole cause being natural variability out of place.

    Comment by Mauri Pelto — 23 Mar 2006 @ 9:24 AM

  62. re 58. Correct spelling is: Judith A. Curry, on CBS Evening News with Bob Schieffer, Superstorms And Global Warming audio video at:
    http://www.cbsnews.com/sections/i_video/main500251.shtml?id=1424013n

    Dr. Judith Curry gave excellent discussion aired on CBS March 20. the reporters on CBS Evening News with Bob Schieffer

    Reporters on the CBS Evening News with Bob Schieffer made an attempt tto ridicule what Dr. Curry had to say by using out dated material, saying that: “NOAA states on its website that increased hurricane activity is not related to global warming”. Dr. Curry followed by saying. “That is misleading”.

    re 61. In reply to comment by Mauri that “This makes NHC stand on the sole cause being natural variability out of place.”, it should be understood that NHC is under the NWS umbrella, and NWS is under the NOAA headquarters umbrella. NWS postion has been that global warming is too political and controversial to comment on, but off the record metorologists with NWS have been telling the public that there is no global warming or global warming problem. That was explained to me a couple years ago by senior meteorologists at NWS Forecast Offices in Minneapolis, Detroit and Chicago.

    Also see post #10463 at yahoogroup called globalwarming, below.
    Feb 25, 2006 9:19 pm
    Subject: Fwd: Re: [Global Warming] Re:PS: Blowing the whistle on climate change: articles
    http://groups.yahoo.com/group/globalwarming/message/10463

    Comment by pat neuman — 23 Mar 2006 @ 10:12 AM

  63. Re: 58, 61, others

    [unnecessarily provocative intro deleted – moderator]

    Have a look at what Max actually said in Congressional testimony:

    “The increased activity [in the Atlantic] since 1995 is due to natural fluctuations/cycles of hurricane activity, driven by the Atlantic Ocean itself along with the atmosphere above it and not enhanced substantially by global warming.” Mayfield did not express a view on global trends. (Webster et al. had just come out the week before.)

    Why might he think this?

    Well, this was the consensus at the time. For example, MIT’s Kerry Emanuel said as much on his WWW site last fall. Since then, this view has certainly not been rejected as untenable, see for instance the agreed-upon Atlantic PDI dataset of Emanuel/Landsea — figure 1 on p. E12 in Landsea’s comment on Emanuel (2005) here:

    http://sciencepolicy.colorado.edu/admin/publication_files/resource-1890-2005.48.pdf

    As Gavin suggests (response to 49) there are legitimate differences of opinions here, and Max’s views are certainly within the boundaries of valid scientific debate.

    It is unfortunate to see RealClimate add to the intensity of this issue by putting people into “camps” using words like “dissenters” to characterize them. For example, Trenberth and Emanuel favor radically different theoretical explanations for the role of global warming in hurricane behavior, but they are lumped together in a single “camp” because they are on one side of the global warming “yes/no” debate. Why isn’t, for instance, Trenberth called the “dissenter” and Emanuel/Landsea put into the same camp, based on their views on theory? The particular framing of scientific discourse into mainstream/dissenters based on the litmus test of global warming yes/no is grounded completely in politics not science, as there are many other scientific taxonomies one might choose.

    The reality is that when Mayfield testified his views faithfully represented the mainstream scientific community. Consider what Emanuel said at the time of his own work, and how he characterized the views of his colleagues, which would include Mayfield:

    “Working with both data and models, I see a large global warming signal in hurricanes. But it remains for me to persuade you and other of my colleagues of this, and it is entirely reasonable for you all to be skeptical…it is, after all, very new. It is not surprising, therefore, that what I have come to believe is at odds with any reasonable consensus.”

    http://sciencepolicy.colorado.edu/prometheus/archives/environment/000554correction_of_errors.html

    If people want to see Max’s views on the science they should have a look at what he has published in the peer-reviewed literature and stop trying to parse individual statements they might come across. Here is a recent paper:

    Pielke, Jr., R. A., C. Landsea, M. Mayfield, J. Laver and R. Pasch, 2005. Hurricanes and global warming, Bulletin of the American Meteorological Society, 86:1571-1575.
    http://sciencepolicy.colorado.edu/admin/publication_files/resource-1766-2005.36.pdf

    NOAA certainly erred when it released that one press release with some unfortunate language about a “NOAA position” – there was no such position. But NOAA as an agency is chock full of outstanding scientists with a diversity of views, and Max is one of them. Under his leadership the NHC last year probably contributed to the saving of thousands of lives. Now people are routinely mischaracterizing his scientific views for what are certainly non-scientific reasons. RC can be a valuable site for scientific discourse, but when it allows unanswered in its comments mischaracterizations and untruths about individual scientists, it takes away from the value of the site. Thanks.

    [Response: Roger, thanks for your clarifications. One interesting point that could be made concerns what the ‘consensus’ was a few years back. I don’t think it was ever that “there is no influence of GW on hurricanes” – that would have been a positive statement of some strength. Instead, the consensus was more like “there is no evidence for the effect of GW on hurricanes” – subtly different, but at the time, much more scientifically defensible (because you never know what the next study will show). The problem with the original “NOAA position”, and with the responses at the end of season press conference was that they specifically used the first statement which I found rather odd and too definitive to be a ‘consensus’. Almost all ‘consensus’ statements go out of their way to ensure that they encompass the possibility that reasonable-yet-unproved hypotheses might at some point be shown to be correct. – gavin]

    Comment by Roger Pielke, Jr. — 23 Mar 2006 @ 10:31 AM

  64. Reply to Kenneth Blumenfeld No. 53

    Actually, as Kenneth Blumenfeld probably knows, people have been looking very hard for trends in extreme rainfall. For example, see the publication by Groisman et al. (2004, J. Hydrometeorolgy 5:64-85) that summarizes some of his group’s work in this area; also consult the IPCC TAR. I think that you will find that, indeed there are published papers reporting trends towards increasing precipitation in the highest precipitation quantiles at least for the continental US. However, others have shown repeatedly (as I cited in J. Hydrol 2006 319:83-95) that increasing precipitation in the highest quantiles does not necessarily translate into increased flooding. As you correctly point out, to defensibly argue for an observed increase in the frequency of intensity of flood events, that by definition are very rare events, requires long-term records – perhaps longer than we currently have.

    That said, that certainly has not stopped people for looking for trends in frequency and intensity of flooding. The studies that I know of generally have not found any evidence for increases in flooding (again see J. Hydrol 2006 319:83-95; and Kundzewicz, Z.W., D. Graczyk, T. Maurer, I. Piskwar, M. Radziejewski, C. Svensson, and M. Szwed. 2005. Trend detection in river flow series: 1. Annual maximum flow. Hydrol. Sci. J. 50:797-810).

    Comment by Tom Huntington — 23 Mar 2006 @ 11:32 AM

  65. re. 63, 31

    Tom Huntington,

    Have you reviewed the NCDC documents (titles below) as part of your work and conclusions in your paper “Century of Data Shows Intensification of Water Cycle but No Increase in Storms or Floods”?
    Are you intending to reply to other questions I asked, in 31?

    Observed Variability & Trends in Extreme Climate Events (PDF)
    Changes in the Probability of Heavy Precipitation (PDF)
    Heavy Precipitation & High Streamflow in the Contiguous U.S. (PDF)
    Precipitation Trends Over The Russian Permafrost-free Zone (PDF)
    Climatic Extremes & Weather Events (Web System)
    Worldwide Weather & Climate Events (Numerous Special Reports)
    The Global Climate of 1997 (Special Report)
    Climate Monitoring Reports & Products (Special Reports, 1998-present)
    U.S. Billion Dollar Weather Disasters (Special Report)
    Climate Variations Bulletin (Monthly Reports, 1994 to Present)
    Climatic Extremes & Weather Events (Web System)
    NNDC Climate Data Online (Interactive Long-Term Climatic Data)
    Storm Events Database (Severe Weather Reports, 1995 to Present)
    Historical Global Extremes
    http://www.ncdc.noaa.gov/oa/climate/climateextremes.html

    Comment by pat neuman — 23 Mar 2006 @ 1:51 PM

  66. Tom,

    Right. Everything you said.

    My definition of “extreme” is more “extreme” than most. I am really talking about the low-frequency, large return-period events (50-year, 100 year), for which it is very difficult to establish trends because of their inherent rarity. Here space (IMHO) is more important than time, and long data series won’t tell you as much as a bunch of tightly-packed 30-year stations. Hershfield (1961) warned of this in the precipitation frequency atlas (US Weather Bureau Technical Paper 40)…yet the focus is generally on getting longer records rather than using space as a surrogate for time.

    I am eager to read your paper and get some of the more recent citations also (my reading on this stopped in late 2003). I appreciate that a comprehensive, up-to-date review is finally out there. Thanks for doing it.

    Comment by Kenneth Blumenfeld — 23 Mar 2006 @ 1:56 PM

  67. Lynn Shay has been working on Oceanic Heat Content for hurricanes at the University of Miami. Here’s the website link: http://iwave.rsmas.miami.edu/heat/

    It is interesting to go back and look at the ocean data last year. The loop current/eddy is very pronounced prior to Katrina, especially when looking at the depth of the 26°C isotherm.

    Comment by Nicholas — 23 Mar 2006 @ 2:09 PM

  68. Re “no evidence”
    I wish (pigs could fly and also that) whenever an agency comments on trends, said agency (or some commenter) would include something informative like:

    “Using statisticics, to say, at the 5% confidence level, that a trend is observed (either increasing or decreasing) requires collecting ____ observations in a year, or ____ observations in ten years, or ____ observations in a century. To find only an up _or_ down trend (but not looking for both)p requires half as many observations, or the number of observations made over half the time period.”
    [Check me on the one and two tailed test requirements, I’m barely an amateur here….)

    There are web pages that allow field workers to find the grim news — how many samples or transects they must obtain, over how long a period, to have any hope of detecting a trend.

    Almost no environmental restoration projects are done with proper baselines. I suspect that’s because — given a good baseline and followup — it’s possible to say for sure that nobody will know what worked for 50 years or so. If you don’t do the baseline you can just do handwaving “isn’t this pretty” to show off the project, ignoring the “and what was it like before you started” issues.

    Comment by Hank Roberts — 23 Mar 2006 @ 2:32 PM

  69. Gavin (repsonse to 63)-

    I pretty much agree, though one slight clarification to your comment about whether the prior consensus was “no global warming” or “no evidence of global warming”. My understandng as an outsider to this literature is that it would be more accurate to say that the immediate prior consensus that the effects of global warming would be real but undetectable. I don’t think anyone has said “no effect” although I recognize that “no detectable effect” might sound that way. Kerry Emanuel is as good as any a spokeperson for the consensus view of the field at that time, and he wrote in 2004 (!!!):

    “Can one detect an actual increase in global tropical cyclone intensity? “Since 1950″ one would expect to have observed an average increase in intensity of around 0.5 m/s or 1 knot. Because tropical cyclone maximum wind speeds are only reported at 5-knot intervals and are not believed to be accurate to better than 5 to 10 knots, and given the large interannual variability of tropical cyclone activity, such an increase would not be detectable. Thus any increase in hurricane intensity that may have already occurred as a result of global warming is inconsequential compared to natural variability.”

    This is a pretty strong, unambiguous statement, and illiustrates how quickly things have changed in this community over the past year. It also helps to put the comments of some scientists who receive lots of unwarranted criticism these days into better context. A consensus does not turn on a dime. The pro- and anti- global warming cheer squads might like it to, but that is just not how science works.

    The reality is that there are today different expectations about what future hurricane/climate research will reveal, and those of us not conducting primary research in this area will have to follow along as those who do hurricane/climate science do their jobs.

    I know of many papers currently in the publication queue that will add diversity to our understandings, and unfortunately no single consensus. I hope that RC will cover the diversity of perspectives on this issue with the same effort as has been focused focused on the Webster group. It is valuable in this instance, and will be in those as well.

    Reference:

    Emanuel, K., 2004. in Hurricanes and Typhoons: Past, Present and Future, R. J. Murname and K.-B. Liu, Eds., (Columbia University Press, New York), pp. 395-407.

    Comment by Roger Pielke Jr. — 23 Mar 2006 @ 3:09 PM

  70. I realize that water vapor has been discussed at length (April 6, 2005), and I understood the argument that water vapor within lower altitudes had a minimal impact on GW. That being said, I was wondering if someone could point me to an article (or discussion) that examined water vapor within the mesosphere that has been contaminated by other greenhouse gases, and any impact this would have on overall global warming or increased hurricane severity.
    I know my naivete is showing, but I am very interested in learning!

    Comment by alisa brooks — 23 Mar 2006 @ 3:32 PM

  71. Re #69: It should be added that KE held to that view right up until he saw the striking results from his study, and that this is when he dropped out as a co-author on your BAMS paper. The consensus may not turn on a dime, but KE’s views sure did.

    One point I want to emphasize is that Max Mayfield/NHC’s understandable focus on the North Atlantic tends to make them want to discount global trends. Add to this the obvious fact that, in the aftermath of Katrina, Adm. Lautenberger and the rest of the Bush administration would really, really, really prefer that U.S. government hurricane forecasters deny any possible current North Atlantic GW enhancement of hurricane intensity (just imagine those headlines), and I think it’s clear that we’ll have to wait until the next administration for a change of tune. The forthcoming season may change all of this, though. While it’s true that another record or near-record season that includes a major strike on the U.S. coast won’t mean much scientifically, the political implications are a different matter. [unnecessary personalisatiom deleted – moderator]

    Comment by Steve Bloom — 23 Mar 2006 @ 4:07 PM

  72. Re #55: Chip, the altimetry data sounds (to my amateur ears) like it’s exactly what is needed, although if the data is available I have to imagine someone is already working on it. OTOH, thinking about it a little more, the altimetry data might be less than perfect for these purposes if it incorporates warm water at depths that might put it out of reach of a cyclone. But maybe some combination of altimetry data with fore and aft SSTs? The task begins to sound large.

    Comment by Steve Bloom — 23 Mar 2006 @ 4:20 PM

  73. Alisa: The mesosphere has very little effect on climate, mostly
    because it is optically thin. ‘Optically thin’ means that it has very
    little effect on light (including infrared light) passing through
    it. It is optically thin primarily because it has a very low
    density. Due to this low density, a light wave passing through the
    mesosphere will interact with very few molecules. Water in the
    mesosphere has very little ability to reflect infrared light back down
    to Earth, because it is so sparse. The greenhouse effect occurs when
    outgoing infrared radiation is reflected back to Earth. Without that
    reflection, the infrared radiation simply escapes, and the Earth is
    not warmed. Mesospheric gasses are also unlikely to have much cooling
    effect on Earth for similar reasons.

    Note: I don’t have the climate expertise many others here do. Corrections appreciated!

    Comment by llewelly — 23 Mar 2006 @ 4:24 PM

  74. RE 68:

    Almost no environmental restoration projects are done with proper baselines. I suspect that’s because — given a good baseline and followup — it’s possible to say for sure that nobody will know what worked for 50 years or so.

    Hank, I enjoy your comments and I think you’re a real plus on this comment board.

    And I have an old GF who did env. restoration for a living, and for years I listened to her concerns (and did some fieldwork in her plots and did grunt labor when needed). Where do I start to explain your statement? The utter and complete lack of money for a typical project (except some Fed projects)? The likely no data on a particular site (pick a site, any site)? The change in focus to population ecology and less atomistic study since the 60s? Reg. changes?

    Best,

    D

    Comment by Dano — 23 Mar 2006 @ 5:07 PM

  75. Re: No. 65.

    I don’t know that I can answer all the questions that you pose. I am sure that I have not reviewed every document on you list. Please read the paper in question and see what I base the conclusion about no increase in floods on. Unlike in the case of the recent papers on hurricane strength, I don’t know of recent papers that report increases in flooding.

    The final wording of news releases are beyond my control. In this instance I argued for a simpler statement that was closer to the title of the paper. Frankly, I was concerned that what I thought was the more influential, other 95% of the paper, would be diluted with the other half of the news release title. I may have been overruled so that the agency could not be accused of choosing which results of the study to emphasize and which not to. Ultimately, I agreed to the wording that was used.

    I have not encountered any censorship in reporting on my research findings if that is what you are getting at.

    Comment by Tom Huntington — 23 Mar 2006 @ 6:10 PM

  76. Thanks llewelly. I really appreciate the information!

    Comment by alisa brooks — 23 Mar 2006 @ 7:31 PM

  77. re 75.

    Tom Huntington,

    I will read your paper on my next trip to the public library. The NCDC website which I made reference to in comment 65 includes a link (below) to the 2001 testimony by Thomas Karl, Director of NOAAâ??s National Climatic Data Center (NCDC).

    Karl’s testimony didn’t mention increased floods, but included these statements:
    “It is likely that the frequency of heavy and extreme precipitation events has increased as global temperatures have risen. This is particularly evident in areas where precipitation has increased, primarily in the mid and high latitudes of the Northern Hemisphere.” http://www.senate.gov/~gov_affairs/071801_karl.htm

    Before 2001 Karl and other scientists at NCDC did research and made public radio interviews on climate change and work related to heavy precipitation, as you can see by the reports referenced in 65, at link:
    http://www.ncdc.noaa.gov/oa/climate/climateextremes.html

    However, in 2001 the research on climate change and the public interviews by NCDC staff stopped, for the most part. I conclude that NOAA headquarters stopped NCDC from doing climate change research, shortly after the change in presidential administrations. Based on what you said in 75, I wish more of us could have been with USGS during the last five years. I think it’s pretty obvious what I am getting at here.

    I’m including a few links (below) on floods in the Red River basin (northern US and southern Manitoba), and North Dakota’s previously closed drainage system called Devils Lake.

    Since 1995, Devils Lake has grown to nearly the size of a Great Lakes.

    Before 1979, floods in the Red River of the North basin were determined mainly by snowmelt runoff in spring. However, the big floods in 1979, 1989, 1997 and 2001 at Fargo, Grand Forks and northward were due to nearly equal portions of snowmelt runoff and rainfall, probably an increasing share being rainfall runoff vs snowmelt runoff, and the snowmelt runoff coming 3-4 weeks earlier (see yellow plot labeled Fargo Red at:
    http://pg.photos.yahoo.com/ph/patneuman2000/my_photos

    Flooding and Climate Change in Southern Manitoba
    http://www.iisd.org/taskforce/pdf/manitoba_geo_survey.pdf

    Devils Lake near Devils Lake, North Dakota:

    Lake Elevation for the Period of Record
    http://nd.water.usgs.gov/devilslake/dvlakepor.html

    Satellite image, data sources
    http://nd.water.usgs.gov/devilslake/index.html

    http://nwis.waterdata.usgs.gov/nwis/nwisman/?site_no=05056500

    http://www.crh.noaa.gov/ahps2/hydrograph.php?wfo=fgf&gage=dcbn8&view=1,1,1,1,1,1

    Comment by pat neuman — 23 Mar 2006 @ 9:05 PM

  78. Off topic (but I don’t remember there being a RC topic on flooding).

    DEVILS LAKE OUTLET: Outlet remains issue in Canada
    GrandForksHerald.com

    Posted on Thu, Mar. 23, 2006
    DEVILS LAKE OUTLET: Outlet remains issue in Canada

    Manitoba premier discusses concerns with prime minister
    Associated Press

    ND State officials still plan to start up the Devils Lake outlet in a little more than a month, but Manitoba officials are still pushing for a more sophisticated water filter.
    http://www.grandforks.com/mld/grandforks/news/14164334.htm

    BTW, Lake Ontario is similar to Lake Erie in length and breadth (193 miles by 53 miles). http://www.great-lakes.net/lakes/ontario.html
    At 1459.0 ft above mean sea level, Devils Lake/Stump Lake spills into the Sheyenne River through Tolna Coulee, at a lake surface area of about 450 sq mi. So, Devils Lake is about 3 percent of the area of Lake Ontario.

    Comment by pat neuman — 23 Mar 2006 @ 11:48 PM

  79. Is what we’re talking about more “frequency of hurricanes (& floods) has not been proven, partly because of meager stats and/or a lot of noise,” rather than a flat definite statement, “there has been no increase in frequency of hurricanes (& floods).”

    This makes a big difference, because I’d like to see the proof at the .05 or less level of significance that there is NO INCREASE IN FREQUENCY OF HURRICANE (OR FLOODS). IE, can it definitely be proven beyond a shadow of a doubt that hurricanes and floods have not become more frequent? (I know science doesn’t work that way, so I don’t expect an answer here, but many lay people don’t know that science is erring on the side of not risking statements about associations…)

    The problem is the media run with, “GW is NOT increasing hurricane frequency or flood frequency,” when is should more accurately state, “scientists have not yet established with high certainty that hurricane and flood frequency is increasing, but climate scientists in general do predict such increases due to GW.”

    I would also add, “Many lay people pretty much guess these are increasing in frequency already.”

    Comment by Lynn Vincentnathan — 24 Mar 2006 @ 2:43 PM

  80. WMO sees link between global warming and hurricanes
    http://tinyurl.com/s7bk2
    Fri Mar 24, 2006 4:58 PM GMT

    GENEVA (Reuters) – There is growing evidence of a link between
    global warming and natural disasters such as droughts and flooding,
    the head of the World Meteorological Organization (WMO) said
    on Friday.

    But Michel Jarraud, secretary general of the United Nations weather
    agency, said more research was needed into the links between global
    warming and extreme conditions like hurricanes.

    Jarraud told a news briefing: “We know for certain that there is an
    intensification of the hydrological cycle, which translates into
    greater risk in some areas of a rain deficit and accentuated problems
    of drought linked to climate change.”

    “In other regions there is a higher risk of flooding and in others a
    risk of greater frequency of heat waves,” he said.

    The WMO said last week that greenhouse gases including carbon
    dioxide — blamed for global warming and climate change — had
    reached their highest levels in the atmosphere.

    Scientists warn that greenhouse gas emissions must be slowed and
    reduced if the earth is to avoid climatic havoc with devastating heat
    waves, droughts, floods and rising sea-levels sinking low-lying
    island states and hitting seaboard cities.

    Carbon dioxide, which the WMO says accounts for 90 percent of
    warming over the past decade, is largely generated by human activity
    involving the burning of fossil fuels.

    “We must accentuate research efforts to better understand the links
    between climate change and a certain number of extreme phenomena,”
    Jarraud said.

    He noted 2005 was a record year for hurricanes in the Atlantic Ocean,
    including Hurricane Katrina which devastated New Orleans.

    “There is not yet a consensus in the scientific community on the link
    between hurricanes and global warming, but there are leads. I am
    fairly confident that in two or three years we will have more
    credible answers,” Jarraud said.

    Research into the link between climate change and El Nino could take
    five years, he added.

    El Nino, caused by interaction between abnormally warm or cool seas
    and the atmosphere, typically triggers drought in eastern Australia
    and Southeast Asia, and floods in western parts of North and South
    America.

    Posted…

    Comment by Tim Jones — 24 Mar 2006 @ 4:55 PM

  81. Being a Pacific guy and not all that familiar with the Atlantic, is there something in the Western Atlantic analogous to the warm pool in the Western Pacific (during the La Nina phase of the ENSO) and to the El Nino “surge” that breaks out when the warm pool has become too massive? Like the Pacific I’d imagine that any warm pool’s build up is driven by the trades and by the wanderings of the ITCZ. One other thing I’d wonder is, of the high intensity hurricanes, which would be thought to be Cape Verde storms? Also, what is predicted to happen with Sahara dust over the time frame in question? And finally, I must wonder about what overall behavior will be expected in the Sargasso Sea over the next 10, 100 and 1000 years, based on the model used for this study, and other models.

    Comment by Steve Sadlov — 24 Mar 2006 @ 5:07 PM

  82. Steve, I recall this recent article; found with Google, along with many more that appear related:

    Atlantic-Pacific Ocean Asymmetry and Past Global Climates II …
    This is thought to account for lower salinity in the North Pacific relative to the North Atlantic, which in turn drives northward flow through the Bering …
    http://www.agu.org/meetings/fm05/fm05-sessions/fm05_PP34B.html

    Comment by Hank Roberts — 24 Mar 2006 @ 5:24 PM

  83. With global warming increasing the sea area over which hurricanes may form and the length of the season in which sea temperatures are high enough for hurricanes, I would expect hurricanes to form further north and south in the Atlantic and over a longer season.

    Given the difficulty in measuring hurricane strength might it not be easier to detect a global warming signal in hurricane dates and tracks? If it is has any such signal been found? Do climate models make predictions about dates and tracks that may be tested?

    Comment by Mike Atkinson — 24 Mar 2006 @ 6:30 PM

  84. re 79, 77

    Flooding and Climate Change in Southern Manitoba

    “Gage records for the Red River in Manitoba have been kept for a little more than 100 years. During that time, the valley has experienced 4 large floods (greater than 3000 m3/s): 1950, 1979, 1998 and 1997. The Red River valley has also experienced considerable climatic variability during the 20th century, including long term temperature increases of roughly 1.5 C. However the influence of these climatic changes on the flood risk in the Red River valley is unclear. Large floods occur very rarely and, given that only four significant floods have occurred in the Red River over the last century, it is difficult to determine if the recent increase in flood frequency represents a real response to regional climatic change or if it simply reflects random year to year fluctuations”….
    http://www.iisd.org/taskforce/pdf/manitoba_geo_survey.pdf

    I wonder if the authors noticed that the 4 large floods all occurred in the second half of the century? Maybe they just figured that fact wasn’t significant enough to mention.

    Comment by pat neuman — 24 Mar 2006 @ 6:53 PM

  85. Re #84 — pat neuman, under some simplifying assumptions, the probability of 4 floods all occuring in the second half of the century is nearly the same as the probability of tossing a fair coin 4 times and getting heads each time, 1/16 = 6.25%. I don’t think this is all that improbable myself, just “unlucky”. Notice that the report states “it is difficult to determine…”

    I opine that it is only by using all the records, wherever obtained, that one might be able to say something about extreme events.

    Comment by David B. Benson — 24 Mar 2006 @ 7:58 PM

  86. … “On April 18, 1997, flow on the Red River at Grand Forks, ND, was 136,900 cfs, and the stage was 52.21 ft, which is more than 2 ft higher than the record set in 1897. The recurrence interval for this peak flow was between 200 and 500 years.” …

    … “The 1826 flood is believed to be the greatest flood in the Red River valley in the last 200 years. The 1826 flood probably was the greatest on many streams in the RRB. From the accounts of the 1826 flood, several conclusions can be can be reached: (1) the fall of 1825 was extremely wet and most of the lakes and wetlands were overflowing, (2) a major snowstorm occurred in late fall, (3) a cold, snowy winter permitted an exceptionally deep snow pack to develop over much of the RRB, and (4) the coldest estimated March-April mean temperature at Winnipeg since 1815, was in 1826.” …

    Excerpt from the Red River Basin Boards Hydrology Team Inventory Report-December 2000, Flood History of the Red River Basin
    http://www.rrbdin.org/about/historical-flooding.jsp

    Also, correction (re 84): 4 large floods on the Red River in southern Manitoba during the last 100 years are 1950, 1979, 1996 and 1997.

    Comment by pat neuman — 24 Mar 2006 @ 8:08 PM

  87. I have one question, as a lay-person who’s just plain interested in listening to the discussions on RC…

    Has anyone along this thread mentioned the Thermo-Haline cycle in the Atlantic Ocean? I only ask because I’m curious what the science community (eg: y’all) have to say about it’s effects on hurricane intensity. It would seem to me that water that is slowing down in movement has a greater chance of holding solar energy at a much higher level. This, coupled with GW (no, not George W. Bush, but please, someone else MUST be thinking that every time they see that acronym), would increase the surface temp of the ocean at a faster rate, right?

    Maybe I’m way off with my questions, and I do not know nearly enough about the science of climatology to fully understand some of the discussion, but I’m a curious bystander, who is happy that discussions such as these on RC are taking place. As an educator in the public schools (albeit, an English teacher), it’s important for me to impress such information upon the students I interact with on a daily basis. Thanks for all of your collective hard work.

    -Thom Palmer
    Dover, NH

    [Response: We discuss this a little here: http://www.realclimate.org/index.php?p=225 -gavin]

    Comment by Thomas Palmer — 24 Mar 2006 @ 8:22 PM

  88. David, I posted 86 then read your 85. I wouldn’t disagree with you on the coin flip example except that I’ve reviewed monthly temperatures in ND and MN since 1880, and temperatures from 1820-2006 at Minneapolis (1903 to 2006 dewpoints). I’ve also done research on the Devils Lake basin. The 1826 very large flood in the Red River basin occurred during a May snowmelt runoff. Floods on the Red River were heavily influence by rainfall. The hydrologic cycle in the Red River basin has undoubtedly changed, regardless of what kind of statistics one chooses to go with on flood frequency and magnitude. Same with Devils Lake. How high will Devils Lake get before it levels off or falls (on a decade basis)?

    Comment by pat neuman — 24 Mar 2006 @ 8:25 PM

  89. Steve:
    NHC definition of Cape-Verde type hurricanes. Note while it is ‘normal’ for an Atlantic hurricane season’s strongest storms to be Cape-Verde type, there are some notable exceptions, such as the 2005 season. Of 2005’s 4 cat 5 hurricanes, only one, Emily was a Cape-Verde hurricane. Katrina, Rita, and Wilma were not.

    With an average of only 2 per year, and a high variance – some years have none, some have as many as 5 – it would much, much harder to detect a climate disruption signal in Cape-Verde hurricanes, than it would be to detect a climate disruption signal in all tropical storms.

    Comment by llewelly — 24 Mar 2006 @ 10:07 PM

  90. To clarify my comment in 88.

    David,

    The hydrologic cycle in the Red River basin has changed because of regional climate change (temperature and humidity increasing), especially winter-early spring. The 1800s-1978 floods were driven by late April and May snowmelt runoff. Beginning in 1979, the hydrologic cycle changed in that snowmelt occurred 2-4 weeks earlier and flood episodes became dominated more by rainfall runoff than snowmelt runoff.

    Same kind of changes are taking place in the Devils Lake basin except for the fact that the body of water has grown. A larger body of water warms and cools more slowly than a smaller body of water, which changes seasonal evaporation rates. Transpiration rates are increasing with the basins due to the longer growing seasons. The changing hydrologic cycle elements (rates of snowmelt and evapotranspiration, volume of rainfall, intensity of rainfall?) that are part of a changing climate and hydrologic cycle within the basin have been ignored by NWS hydrologists in their modeling, public probabilistic products and flood predictions. From Jan 2000-July 2005 I tried to change that, but failed.

    Comment by pat neuman — 24 Mar 2006 @ 11:07 PM

  91. Pat,

    If you want to track down the coop observer sites in the basin (DL or RR), plus any other dense networks that may be out there( for example, the soil-water conservation districts often have gauges; the Future Farmers of America used to have a pretty extensive network too), I’d be happy to take a look at the data with you to see if indeed there have been significant changes in precipitation extremes. Anything on the MN side is available from the Minnesota State Climatology office. I think you have my email so we could take this off-list.

    Comment by Kenneth Blumenfeld — 25 Mar 2006 @ 2:40 AM

  92. To conclude that anthropogenic warming substantially enhances the strength of hurricanes involves three logical steps:

    (1) Warmer SST significantly enhances the strength of hurricanes.
    (2) Anthropogenic warming significantly raises SST in the relevant regions.
    (3) Anthropogenic warming has no other effects (like reducing vertical gradients) which mostly or fully cancel the SST effect.

    To confidently claim that the rise in hurricane energy over the past decades is entirely due to a natural cycle (as the NHC has done), you have to be confident that at least one of the three points above is wrong.

    Hurricane forecasters like the NHC people know a lot about (1), much more than I do, and they don’t seem to question this statement (note that the statement is not that SST is the only or dominant effect – just that it is important).

    Point (3) is a possibility raised e.g. by Isaac Held in our comments section last year, and it can and needs to be discussed by serious researchers. However, at this stage there is little evidence to suggest that the SST warming effect is compensated in this way, and the data of Emanuel (2005) and Hoyos et al. (2006) speak against it. Therefore, we can’t rule out that (3) is wrong, but I don’t think that anyone could claim with any confidence that point (3) is wrong.

    That leaves us with point (2), and indeed it is the one questioned by those who claim the rise in hurricane activity is natural. They claim that the relevant increase in SST is entirely part of a natural cycle, namely an increase in thermohaline ocean circulation in the Atlantic. As an oceanographer I do not think this is a supportable scientific position; it certainly is not a position that was consensus just a couple of years ago (see comment #63), and it goes against everything we know about global warming. This position would require that the effect of greenhouse gas warming somehow magically leaves out the tropical Atlantic (no model suggests this), and that the tropical Atlantic by chance has naturally warmed just by the same amount as the rest of the global SST but for a different reason. Have a close look at the comparison of tropical Atlantic SST changes with northern hemisphere temperature changes by Kerry Emanuel here. Or look at a global map of SST trends over the past decades: you don’t see anything special going on in the tropical Atlantic – similar warming happens in the tropical Pacific and Indian oceans, and most of the rest of the world. Also, the supposed increase in thermohaline circulation is not a measured phenomenon (quite unlike the rise in greenhouse gas concentrations) so one cannot be very confident that it is even happening, let alone that it is the sole effect that explains the SST rise in the tropical Atlantic. Therefore, in my view the press conference of the NHC, where they claimed with confidence that the rise in hurricane activity is natural, will be remembered as one of the darkest hours in the history of NOAA.

    Comment by stefan — 25 Mar 2006 @ 7:21 AM

  93. re 90 91

    Surface and interflow runoff are the largest components of runoff contributing to river flooding. Baseflows and reservoir regulations affect streamflow to a smaller degree. Antecedent storm conditions influencing the amount of surface and interflow runoff include: states of soil moisture and soil temperature, vegetation and snow cover, and the intensity, amount, and type of precipitation from the storm.

    In the Upper Midwest, climate change is increasing the amount of surface and interflow runoff because heavy rainfall is occurring earlier in the spring, before the vegetation is established. Establishing vegetation depends on the amount of daylight and sun angle, which won’t change with time, and also depends on day-to-day air temperatures for a season. Rainfall from February to mid-May has been increasing before vegetation gets established, leading to larger degrees of surface and interflow runoff, more erosion and more flooding. Based on operational experiences … not allowed during my career with NOAA NWS NCRFC to do research for peer reviewed papers that were related to political and controversial subjects like regional climate change and global warming.

    Comment by pat neuman — 25 Mar 2006 @ 11:19 AM

  94. RE #85 & coin-flips. You certainly cannot disprove that the coin is loaded for heads, esp if 4 came up in a row.

    So what is better: assume GW is not happening & not causing increase havoc, & do nothing; or think that GW might be happening & wreaking havoc, and, say, turn off lights not in use, etc.

    Comment by Lynn Vincentnathan — 25 Mar 2006 @ 12:02 PM

  95. re 93. should read “Establishing vegetation depends on the amount of daylight and sun angle, which won’t change with time” from year to year”, …

    Also, for example of discussion in 93, may see:

    “The Spring Flood Outlook products are seasonal products issued in February and March which provide forecasts of the flooding expected due to snow melt for river basins within the North Central River Forecast Center area of responsibility.”
    http://www.crh.noaa.gov/ncrfc/?n=ncrfc_spring_outlook_20060309

    and

    “North Central River Forecast Center Long Range Probabilistic Outlook Summary Valid February 23, 2006 – May 24, 2006
    http://www.crh.noaa.gov/ncrfc/content/seasonal/outlooks/2006/rls0223/outlook_summary/esptable.php

    and,

    Featured Products from NOAA/ National Weather Service
    National Centers for Environmental Prediction
    Hydrometeorological Prediction Center
    http://www.hpc.ncep.noaa.gov/

    Comment by pat neuman — 25 Mar 2006 @ 12:49 PM

  96. Re #49 and “Does all of this really matter? AGW is happening and mitigation activities are needed regardless of what is going on with hurricanes. Shades of the hockey stick!

    Every intuition tells me that GW should affect hurricanes. However, my intuition is not science. I am concerned with the possibility that some of the very excellent scientists on this site may have foregone their science and succumbed to a similar intuition.”

    BPL replies:

    I took the satellite temperature anomalies (differences from mean world temperature over the period) from December, 1978 to August, 2005. My source was NASA’s Global Hydrology and Climate Center (on the web at http://www.ghcc.msfc.nasa.gov/ghcc_home.html).

    This gave me 321 data points. I divided them into two groups of as nearly equal size as I could get, December 1978 to March 1992 (N = 160) and April 1992 to August 2005 (N = 161). I calculated descriptive statistics for each group:

    number: mean: std. dev:
    160 -0.0230 0.106
    161 0.167 0.216

    The equality of two standard deviations can be tested for with a Fisher’s F test:

    F = s1^2 / s2^2

    where s1 is the larger standard deviation and s2 the smaller. The respective sample standard deviations each have N – 1 degrees of freedom. In this case, I found F(160,159) = 1.67. For the sample sizes involved, this result is significant at the 99.9% level. It is overwhelmingly likely that the later period is more variable than the early period.

    As the atmosphere heats up, it carries more energy, so we can expect weather to be more variable.

    Comment by Barton Paul Levenson — 25 Mar 2006 @ 5:50 PM

  97. re 91.

    Kenneth,

    To look at changes in precipitation intensity, we’d want hourly time steps from radar/gage mosaic-ed HRAP cells (idea used to justify money for NWS AHPS).

    Comment by pat neuman — 25 Mar 2006 @ 6:25 PM

  98. Re #95: Lynn, my point was only that attempting to make predictions based on only 4 extreme events doesn’t give one much confidence. My apologies for not being sufficiently clear about that. BPL’s #96 involves enough data to be meaningful. Even better, see all the commentary regarding Tom’s paper in J. Hydrology.

    Comment by David B. Benson — 25 Mar 2006 @ 6:33 PM

  99. re 96. 98.

    BPL,

    As the atmosphere heats up and becomes more humid, variability in average temperatures is less (not more), based on climate station data since 1880 in the US and shown by time series plots at:
    http://pg.photos.yahoo.com/ph/patneuman2000/my_photos

    Comment by pat neuman — 25 Mar 2006 @ 6:50 PM

  100. Stefan, about point 2:
    As far as I have read, in recent years it seems that the THC has slowed down, which may lead to an increased area of higher SST’s in the (sub)tropical North Atlantic (due to less poleward heat movement), which may increase hurricane frequency and intensity (for the latter, if there is an increase in temperature in the deeper oceans), but the temperature gradient between tropical and extra-tropical SST also may play a role too (which may be a part of point 3).
    If the slowdown of the THC is a result of increased GHGs or part of a natural cycle is a matter of debate, but more important is that there is another natural component that has a huge impact: the change in (low) cloud cover in the (sub)tropics in the past decade(s).

    According to Wielicki ea. and the accompanying Chen ea. paper, there is an increase of ~2 W/m2 in direct insolation over the whole (sub)tropics in the period 1985-2000. This is confined to the tropics (30N-30S), while the influence of GHG’s is more evenly distributed over the whole earth’s surface. The increase in ocean heat content is specifically high in the NH subtropics, see Fig. 2 in Levitus ea., and coincides with the decrease in cloud cover (and the increase in insolation), which points more to cloud/insolation influences.
    Thus even if the NOAA points to the wrong cause, natural influences can’t be ruled out and may be more important than increased GHGs.

    It may be interesting to look in more detail at the (deep) ocean temperature trends and the cloud cover trends in the main area of tropical cyclone development in the North Atlantic…

    [Response: One of the nice things of our RC website is that the layperson can lecture the expert who’s been working for his entire career on THC. But let me return the favour: your idea that the North Atlantic tropics warm up if the THC slows down is a common misconception, see the graphs in this post. The idea of a number of hurricane researchers, namely that the tropics warm up when the THC speeds up, is physically correct, except that this cannot explain much (let alone all) of the observed warming of the Atlantic tropics of the past decades. For many papers on THC and its effects on climate, see the publications list on my home page. -stefan]

    Comment by Ferdinand Engelbeen — 26 Mar 2006 @ 9:39 AM

  101. Re #100 (comment)

    Thanks Stefan for your comment. Although I have spent halve of my professional life as process engineer, amongst (many) other things involved with heat flow (be it for chemical processes), I learn everyday a bit more…

    As far as I have read in several of the messages and publications, the THC is the most important item in heat flow from the Atlantic equator to the North Atlantic.
    In a simple heat exchanger, if the heat flow is reduced for any reason (like scaling) the side of the heat source will become hotter (even to rupture in extreme cases) while the heat inflow remains constant, and the other side gets colder. Of course, the oceans are not such simple constructions. But a continuous positive heat inflow at the equator with a reduced heat flow to the poles must lead to an increased heat content (and temperature) of the equatorial oceans, if the laws of thermodynamics still hold. This may be dissipated to the SH (as the graphs you pointed to indicate), but there is little southward surface flow in the Atlantic and I suppose that at least some of the heat should remain in the tropics (as one need a driver for general increased southward flows)…

    Of course, there are other means to dissipate heat to space and other parts of the earth. Like storms and cyclones, changes in cloud cover and air currents. But the latter seems to reduce in a hotter environment too (see Fedorof ea.).

    But, that was not the most important point in my comment. The increase in heat content / temperature of the North Atlantic subtropics may be the result of recent changes in cloud cover, which is – according to Chen and Wielicki – probably all natural. And interesting enough to start a more detailed investigation.

    Btw, the Nature article about the possible solar origin of the 1470 yr climate cycle during ice ages, triggered by shorter cycles, is very interesting.

    [Response: If you’re an engineer it is very easy to understand: the northward branch of the THC flows from South Africa through the Atlantic right up to the Nordic Seas, and it flows through the region we’re talking about (i.e., the hurricane region, ranging roughly from 10N to 30N). It enters this region from the south (coming across the equator) at a warmer temperature than it leaves this region with the Gulf Stream at, say, 30 N. Therefore, the THC acts to heat this region – more so when the THC is stronger, and less when it is weaker. Hope this is clear? You were just looking at one end, and forgot to take into account the connected inflow at the southern end. -stefan]

    Comment by Ferdinand Engelbeen — 26 Mar 2006 @ 8:20 PM

  102. Re #92: Thanks, Stefan, for that very neat summary. As I’m sure you know, it has long been rumored that that we will be seeing a paper by the NHC’s Bell and Chelliah outlining their case for natural cycle causation. It sounds as if you haven’t seen it or that you’re obligated to stay quiet about its contents as a condition of having seen it pre-pub. Bell will be giving a talk on this subject at a conference in NYC that Chris Mooney will be attending next week, so I imagine we’ll be seeing something on his blog shortly after that.

    What do you think of the Japanese study Chris quotes in #41?

    [Response: Bell and Chelliah (2006) is now available here: http://ams.allenpress.com/amsonline/?request=get-abstract&doi=10.1175%2FJCLI3659.1 – gavin]

    Comment by Steve Bloom — 26 Mar 2006 @ 8:56 PM

  103. > tropics warm up if the THC speeds up
    Perhaps — just guessing — there’s a minimum amount of time any given parcel of water has to reside in the tropics, to pick up all possible heat? If so, a slower THC lets the water hang around to pick up more heat, while a faster THC moves each parcel of water on through while it hasn’t picked up all it could, leaving more behind

    That’s of course ignoring much else. Just saying it can’t be that simple a thermodynamic heat exchanger — much else going on. How much mixing happens while a parcel of water is there, does the THC water always move on the surface or can it slip past below the warm surface, etc.

    Isn’t the AURA satellite study due to be providing some info soon on the whole question of what’s happening with convection in the tropics (from flights in January and February of this year by NASA)?

    Comment by Hank Roberts — 26 Mar 2006 @ 10:28 PM

  104. Re #s 100 and 101: Ferdinand, in #100 you use the phrase “natural influences can’t be ruled out,” which is fair enough, but then like Dr. Strangelove’s arm out pops “probably all natural” in #101. It seems that you are compelled to presume natural causes in everything. Just out of curiosity, why? But anyway, here are the relevant quotes from the relevant papers:

    Wielicki et al: “Whether the changes seen in the radiative balance in the last two decades are the result of natural variability or are a response to global change remains to be determined.”

    Chen et al: “The possibility that lapse rates were decreasing instead before 1980 (23) suggests that the observed intensification of the Hadley-Walker cell may be due to natural variability on decadal or longer time scales rather than to a forced climate change; however, the length of the satellite data record is too short to distinguish between these two driving mechanisms.”

    That seems clear enough.

    Also, with regard to your comment that this would be a fruitful area for more research, note that those two papers are about four years old. Haven’t those authors or anyone else done further work by now? If not, given the timing of the AR4, wouldn’t it be fair to say that this line of research has been abandoned? But please do check and let us know if you find anything that’s more up to date.

    Comment by Steve Bloom — 26 Mar 2006 @ 11:27 PM

  105. Re #s 100 and 101: Well, Ferdinand, it appears it might be a dead end after all, although I didn’t have time for a thorough search so don’t just take my word for that. Have a look at the comment by Trenberth in the same issue of Science as the two papers, the response to the comment and then the remarks on page 6 of the more recent review http://www.cgd.ucar.edu/cas/trenberth.papers/CLConfPaperds.pdf . It’s not clear how much is left of the issue at this point, but perhaps not a lot other than the perennial satellite calibration problem. If you don’t have a Science sub, let me know and I’ll email you the comment and response.

    Comment by Steve Bloom — 27 Mar 2006 @ 12:13 AM

  106. Re #104 and #105,

    Steve, the issue of instrument accuracy and decay is indeed one of the most important problems as good as on earth (an engineers joke: one instrument in a line is always exact, until you fit a second in the same line…) as even more problematic on satellites. This has given much discussion and reason for corrections in the past (and probably in the near future), until new generations of multi-material/physical different and self correcting instruments are in use. Thus I can understand (and hope with) Trenberth that a lot of money will be spend on better methods to measure and understand what really happens with our climate.

    But despite the (relative small) problems with the radiation budget satellite instruments, even recent (Science May 2005) publications with corrected data show an increase of 0.16 W/m2/yr of global insolation in the period 1983-2001. In the full article, the trend in the tropics is described and even more pronounced: 0.18 W/m2/yr, or over 3 W/m2 for the full period (but in fact increasing only after 1990) of measurement. In the tropics, the difference is mainly (if not completely) from changes in cloud cover.

    This brings us to natural or not. The change in CO2 levels 1983-2001 is app. 30 ppmv. This results in a radiation change of app. 0.3 W/m2 over the full period. This is one order of magnitude less than what is observed. This all points to natural variability.

    Chen and Wielicki use stronger statements in “A Delicate Balance” pages of NASA:

    “We are likely seeing a decadal fluctuation here. Right now we are looking at what might lead to such a fluctuation,” says Chen. He believes that this is a natural climate anomaly much like El Nino, La Nina, or the North Atlantic Oscillation. It is a natural part of the rhythms of the Earth’s climate system. But unlike these other anomalies, the Hadley-Walker cell fluctuates over the course of decades instead of years. Chen feels that this phenomenon has no direct relation to global warming or any other hypothesis related to climate change, including the Iris Hypothesis.

    and

    Wielicki agrees with Chen’s assessment. He adds, “What we are seeing is that the climate system has multiple ways it can arrange itself and still accomplish a heat balance. In this case as the clouds change, the Earth absorbs more heat at the surface while it radiates more heat from the atmosphere.” Wielicki explains that even from the start, this phenomenon appeared to be a climate fluctuation unrelated to global warming or greenhouse gases.

    And have a look at the last pages, which compare the results of climate models and observations. I don’t know if AR4 models are better in equatorial (and Arctic) cloud cover/radiation balance calculations, but if not, then they still are not very good in projecting any future climate…

    Comment by Ferdinand Engelbeen — 27 Mar 2006 @ 6:53 PM

  107. Re #101 (comment)

    Thanks Stefan for your comment. I was wondering where the inflow was for the THC, which – in the rough schematics – comes all the way from near Antarctica. Still there are some problems with the overall picture: If one looks at the different Atlantic currents of interest at the Miami University graphs (the Carribean current, the loop current, the Gulf stream and the subtropical countercurrent) for seasonal temperatures, then it happens that the highest temperatures in the summer months, leading to tropical storms are in the 10N-20N band (including the Gulf of Mexico), thus an increase of inflow from the South (due to increased outflow via the Gulf Stream) should have a cooling effect… But an increase in the other seasons can create already warmer waters for the next hurricane season…

    All together quite complicated and rather counterintuitive…

    Comment by Ferdinand Engelbeen — 27 Mar 2006 @ 8:12 PM

  108. I have followed the THC discussion with some interest as the speeding up of such has been used as a shrill argument to explain the increase in intensity of hurricanes in the North Atlantic. Alas, it is a pity that the explanation fails even in the NATL (Bryden et al.). Even if it were successful (i.e., sans Bryden’s research) it would have difficultly explaining like increases that occur over the globe. So without the THC argument, there is a need to find a “global mechanism” to explain the universal change in hurricane characteristics. And Chelliah and Bell (2004, 2006) appear to have such an explanation with the finding of a 100-year cycle called the Tropical Mulitdecadal Mode which, more or less, has a common sign over the tropics.
    Alas, there are problems. C&B use the NCEP/NCAR reanalysis constructed for the period 1950-2000 or so to define a 100-year cycle. The problem is how do C&B differentiate between a 50-year trend and a 100 year oscillation using a 50-year data set? Statistics are tricky things and EOF or Principal Component packages are very adept at producing oscillations longer than the data set if the data set is not detrended.
    Why bother with papers that may have such very basic statistical flaws? Well, these are the papers quoted by NOAA administration in their statement that global warming has nothing to do with the changes in hurricane characteristics during the last decade.
    Please expect vigorous comments (peer-reviewed) on the latest Chelliah-Bell paper.
    PW

    [Response: For that matter, with a 50 year record, how do you distinguish one “mode” which affects SST more or less globally from the global warming trend, which does rather similar things? It sounds a little like the fancy statistics of Bell and Chelliah have just succeeded in renaming the AGW signal the “Tropical Multidecadal Mode.” –raypierre ]

    [Response: Good point. If the tropics had warmed more (or with a differnt time evolution) than the global mean, I’d be looking for a special tropical phenomenon to explain it. But they haven’t. So if you want to explain tropical warming by a special tropical mechanism, you’d also need to explain (a) why this mechanism works exactly in step with global warming, and (b) why anthropogenic global warming has spared the tropics, so that there is room for another explanation. See my comment #92. -stefan]

    Comment by Peter Webster — 27 Mar 2006 @ 9:49 PM

  109. Re #106: Ferdinand, thanks for citing to a more recent paper, but please note that it doesn’t lend support to your contention that “this all points to natural variability.” The NASA page you quote is just a re-hash of the 2002 papers and is equally out of date. Also, you should have a look at the three related papers and articles in that same May 2005 issue of Science.

    Finally, I’m a little mystified as to the implications of your calculation of CO2 forcing. See http://www.realclimate.org/index.php?p=220 .

    Comment by Steve Bloom — 28 Mar 2006 @ 5:34 AM

  110. Re #109:

    Steve, the comment of Chen and Wielicki doesn’t need an update, as their original calculation came with a 2 W/m2 increase of insolation in 1.5 decades, while the newer work calculates this as over 3 W/m2 in a similar period.
    The calculation of CO2 forcing for different concentrations can be done at the Archers site. You need to fill in the amount of CO2 for 1983 (~340 ppmv) and 2001 (~370 ppmv), both without changing the rest, except for tropical atmosphere, measurement at 0 km and looking upward. The difference between the two results is what gives you the extra amount of heat coming back to the surface, due to the increase of CO2.

    Of course, this is without water feedback (but that seems to be negative in the period of interest: -upper- tropical humidity reduces with higher Hadley/Walker cell speed) or other feedbacks, but these are probably of lesser importance than CO2 and water (except for clouds). The other important greenhouse gas, methane, has (in the Modtran program) no measurable addition to the result.

    Thus the calculated increase in forcing by CO2 is ~0.3 W/m2, while the observed increase by solar forcing (mainly from cloud cover changes) is ~3 W/m2 in the same period of time. Only if there was a direct short-term strong (tenfold!) influence of CO2 changes on insolation via cloud cover, then this could be mainly/all anthropogenic. But the period 1983-1990 shows a decrease in insolation, with increasing CO2 levels. Thus the change in insolation (and consequently most of the recent warming in the tropical oceans – and beyond?) is largely of natural origin.

    The other related papers in part reinforce the foregoing reasoning.
    The first paper by Charlson ea. points to differences in results between methods to detect changes in radiation budget, calculated as equivalent changes in albedo.
    But several methods detect large changes in radiation budget (in both directions) within 1-2 decades, at the same order of magnitude as the change in GHGs since the start of the industrial revolution…
    The Wielicki e.a. paper is not relevant here, it only discusses the satellite vs. earthshine differences, where satellite measurements are more consistent with observations.
    The paper of Wild ea. confirms that the change in insolation is much too large (decline 6-9 W/m2 1950-1990, increase ~5 W/m2 1992-2001) and variable in sign to be of anthropogenic origin. Neither GHGs or aerosols can explain these near worldwide changes (even in the low aerosol SH). Water vapor/cloud changes seems to be better candidates…

    [Response: Ferdinand, if you’re trying to understand the greenhouse effect by looking at the effect of CO2 on the downward IR into the surface, you are misguided. See my post on “A Busy Week for Water Vapor”. As for the rest, I’ve tried by I really don’t see what point you’re trying to make. You are just quoting a lot of random observations without any real understanding of what they mean. –raypierre]

    Comment by Ferdinand Engelbeen — 28 Mar 2006 @ 7:19 PM

  111. Re #110 (comment)

    Raypierre, as usual (bad habit of mine) I was going too fast…
    The discussion was triggered by the comment of Stefan in #92. There he concludes that the increase in SST (and thus tropical cyclones) in the relevant area can not be explained by natural causes. The influence of GHGs may be true (in part) over the long term (1945-2005), but there is a large natural fluctuation, of the same order as the total GHG forcing since the start of the industrial revolution, with a frequency of 2-4 decades (or longer) over the same area. That the change in direct insolation in the tropics (coupled to cloud cover changes) is natural was challenged by Steve Bloom, but it is hardly possible to blame that on GHGs, if the sign of the insolation changes follows its own rhythm, unrelated in area and time frame to aerosols and GHGs.
    Of course, the change in CO2 induced forcing is only a part of the greenhouse effect story, but some of the feedback effects in this specific case, especially water vapor, seems not to follow the normal rules (less upper tropospheric humidity, hence less cloud cover in the down welling branches and overall tropics). But that may be different at lower levels (due to higher SSTs). Anyway, CO2 changes in the past 1-2 decades can’t explain the large change in heat content/SST in the tropics for the most recent period, while one order of magnitude larger changes in forcing by clouds/insolation can do that job.

    Therefore it may be of interest to look at the specific area of interest (and southward to the inflow areas) for areal changes in cloud cover and insolation…

    Comment by Ferdinand Engelbeen — 29 Mar 2006 @ 6:28 AM

  112. In reference to #73: I really do appreciate your answering me without blasting me, but I’m going to stick my neck out one more time on the same issue. Please don’t hit me too badly for being dense.

    I understand that the mesosphere CURRENTLY has very little effect on GW. But reading the following articles keeps me coming back to the question: If GHG is contributing to a colder, denser mesosphere (by way of ice formation triggered by some sort of pollutant), wouldn’t this eventually have a significant effect in overall GW.

    http://geo.arc.nasa.gov/sgp/aero/aerocloud3.html

    http://www.gsfc.nasa.gov/gsfc/earth/atmos/ozone.htm

    http://aim.hamptonu.edu/

    I promise I’ll not bring this up again if I’m reading the wrong papers, have totally missed the mark on what the papers are trying to convey, or am totally off base.

    Thanks!

    [Response: It’s absolutely clear that gaseous radiative effects in the mesosphere have essentially no effect on the Earth’s radiation budget. With clouds, it’s not completely obvious from a back of the envelope calculation, since a quite tiny mass of cloud particles can have quite a large effect, particularly if the particles are very small. Titan’s haze clouds, which have the dominant effect on that body’s radiation budget, are all in the very outer reaches of the atmosphere, which has a tiny share of the atmospheric mass. Shaidlov’s preprint (discussed in the “Meteors, Nuclear Weapons, etc.” posting, is still nonsense,because (among many other things) he argues in terms of the gaseous effect of mesospheric water vapor, not a presumed cloud effect. I have never heard that mesospheric clouds have any significant effect on the radiation budget of Earth. Indeed, they are much optically thinner than polar stratospheric clouds, and the latter already do hardly anything. Without knowing more about the mesosphere, though, I couldn’t easily rule out that mesospheric clouds could never do much. Are there any mesosphere experts out there that could chime in on this matter? –raypierre]

    Comment by alisa brooks — 29 Mar 2006 @ 12:06 PM

  113. Alisa, what led you to asking about the mesospheric clouds, if I may ask? Sometimes it helps to know where you found the info that inspires the question. I asked something similar recently — I was confusing polar stratospheric and noctilucent clouds); something I’d read five years ago didn’t distinguish between them.

    Llewelly’s answer to your 73 was about gases, but your question is about clouds (I think there are clouds other than water ice — but again I may be confusing stratospheric with mesospheric clouds).

    Reading your links (disclaimer –I’m an amateur here, just a reader)
    — the first is fascinating for astrobiology, if it’s discussed anywhere else please point me there.
    — The second is to Drew Shindell’s info on the 2000 ozone hole, and stratospheric clouds, the ones where the ozone chemistry is happening. The newer info from that area isn’t encouraging, it’s discussed elsewhere at RC.
    — The third link is the home page for NASA’s AIM satellite — currently being built. Once in orbit that program can start collecting data toward the very question you ask, and it appears to have been designed specifically to look at mesospheric clouds, changes in them recently, and climate effects they may have in the future.

    It’s not clear whether they are increasing, from what I read, or whether they mean the photos from the Alpha, er, the International Space Station, are showing more of them developing, or just that they can see them.

    So — if your question is “would changes in mesospheric clouds change climate” then the answer may be on the AIM satellite’s Mission page:

    “These data can be obtained only by a complement of instruments on an orbiting spacecraft because of the need for global coverage and because extinction and foreground emissions compromise optical sensing from the ground.”

    Maybe our hosts can invite someone from that project to start a topic on the satellite, though before it flies, I suspect they’re just as curious as we are! But they could talk about why they got the project going, there must be some interesting chemistry behind the proposal being funded.

    Comment by Hank Roberts — 29 Mar 2006 @ 1:06 PM

  114. Thank you Hank!

    My question was based on conversations regarding:
    Meteors, Nuclear Tests and Global Warming

    Shaidurov’s paper prompted me to find relevant information related to noctilucent clouds. From there I started looking at where they were formed (at what altitude), then how the mesosphere functions and interacts with our current climate. I then became curious to find out the effects continued pollution may have on it (if any). This all lead me to my question.

    Thanks Hank!

    Comment by alisa brooks — 29 Mar 2006 @ 2:12 PM

  115. Ferdinand, what I challenged was your citation of those dated papers in support of your assertion that the referenced change is “probably all natural” (from comment #101). I probably sounded a little exasperated because you’ve referred to the same papers in support of the same idea on at least a couple of other occasions on RC.

    The citation part is just a matter of blog etiquette — I know it’s a pain to do the research, but it’s very misleading to people reading this site to not check your own work prior to making comments of this sort. The authors are volunteers, and expecting them to step in and make corrections every single time on such things is unfair. In any case, you’re obviously very keen on the science and should want to know what the current thinking is.

    Of course the interaction between the AGW signal and natural variation is complex and not perfectly understood, especially when it come to clouds, but the science simply doesn’t support an assertion of “probably all natural.” If you can quote a paper or climate scientist saying so, great; if it’s just your opinion, please make clear that it’s you and not the paper or scientist.

    Comment by Steve Bloom — 29 Mar 2006 @ 2:56 PM

  116. Re #115

    Steve, my fault, I am reading pretty much about climate these days and pick up the interesting parts of different publications and what I write is mostly a syntheses of my view of what I have read.
    In the case of the Chen ea. and Wielicki ea. papers, the basic information (that there are huge changes in radiation budget in the tropics as result of cloud cover changes) didn’t change since 2002. The opinion of both is that this is a natural phenomenon (as expressed on the NASA web site).

    If you have a look at the heat budget of the oceans by Levitus ea., in figure 1, one can see a cooling trend in the period 1980-1990 and a warming trend 1990-2000+. This coincidenses with the periods of “global dimming”, where there is a decrease in insolation in the previous period and an increase after 1990 for most of the observations. This also coincidences with a decrease and increase of cloud cover and more/less reflection of (short wave) sunlight in the tropics (and beyond).
    And it differs from the emissions of aerosols: sulfate emissions are rather steady-state since 1975 (sorry lost the reference, thought it was on the IPCC site), but with a large regional difference: huge reductions in Europe (and N.A.), compensated by a huge increase in SE Asia. But in both cases (except India) there is an increase in insolation after 1990 (see Wild ea. Fig. 1). GHGs may contribute to the overall increase 1945-2005, but can’t be responsible for the huge cooling 1980-1990.

    Thus the recent increase in tropical heat content/temperature and Atlantic cyclone activity is largely a result of (a) natural cycle(s) (as the work of Bell and Chelliah also alludes to), and in part of GHGs forcing over the long term. But what drives what in the natural cycles is quite difficult to know…

    [Response: As noted previously, Bell and Chelliah can be discounted, since there is no way then can discriminate long term “natural” variability in the data they are using. Also, among many other things, you are making far too much of the Wielecki study. The authors themselves were very cautious about their results, both as to whether they are real and whether the changes were triggered in part by GHG. Splicing together multiple satellites into a long time series is perilous, and their caution is justified. As noted in the Trenberth article cited in Comment 105, yet another error was discovered in 2004, which needs to be taken into account. I wouldn’t be surprised if there were more to come. It took a long time to shake out all the problems with the MSU data analysis, and in some ways even that work isn’t done yet. There is no question that at least part of the tropical warming is attributable to GHG increases, at least since the 1970’s. If you are saying that some part of the warming may also be due to natural variability, that’s certainly in the cards but it doesn’t in any way follow from the arguments you are making, even if Wielecki’s data were right. Finally with regard to global dimming, you have to distinguish between changes in the surface insolation and changes in the top of atmosphere radiation budget, which are quite different things and have quite different effects on climate –raypierre]

    [Response:There are a few other points to keep in mind about the widely misinterpreted Wielecki et al study. First, there is no manifest evidence even in that paper for a large net driving of climate by the fluctuations they see (even if they are real). Look at the bottom panel of Fig. 2, which gives the net top of atmosphere tropical flux. The big event you see there is Pinatubo, but there is no long term trend in the TOA net. Now, to make life even more complicated for you, if the SST has time to come into equilibrium you wouldn’t expect to see any change in the net TOA budget even if CO2 (amplified by feedbacks) were causing a large surface warming during this time, or even if you were completely right and cloud effects were causing a warming. That’s because, once things reach equilibrium, what goes in must equal what comes out. All you can see in the TOA budget, without making use of a model in the interpretation, is the disequilbrium. This makes the data completely unsuitable for trying to draw the kinds of conclusions you are after. Now, the real significance of the paper is in Figure 3, which suggests (remaining to be confirmed) that models have some problem with the seasonal cycle of tropical clouds. This is not completely news, since we know many ways models have problems with clouds, but the observations certainly will help modellers fix things. I’m less concerned by the problems in the simulated trends in Fig. 4, since that may go away with further satellite data processing, and the simulations used were not the optimal ones for comparing with data of this type. Finally, I have taken the time to provide you with some detailed feedback on your misinterpretation of radiation budgets this time, but you’ve introduced the same faulty reasoning many times over, so please don’t expect me to comment any more on this topic. Readers will please not jump to the conclusion that I agree with Ferdinand just because I refrain from responding to future arguments of this type. –raypierre]

    Comment by Ferdinand Engelbeen — 30 Mar 2006 @ 6:59 AM

  117. On repeating corrections — a plea.

    Many discussions online bog down and die when dogged repetition overwhelms attempts at citation, explication and comprehension. At which point the thread gets taken over by disinformants advertising PR talking points. Choke.

    I’m sure that’s not your intent, but beware the outcome: plopping one idea no one supports into many threads hides your other contributions. Readers get exhausted — it’s like using the same lunchmeat in everything on your menu, eh? No matter how tasty, repetition overwhelms the taste.

    Can you pick one place and you can work it out mathematically, post your cites, let us read and discuss and watch people with some expertise check the math and perhaps find someone who has experimental results on it?

    And to Raypierre — please don’t stop correcting (maybe an index of Frequent Unsupported Hypotheses is needed, there are plenty — if the comment software here supports posting a link instead of repeating a correction — would serve everyone well.

    And to all — please, use blank lines and paragraphs? Aging eyes need some formatting.

    Blush. Sorry for the run-on metacomment.

    Comment by Hank Roberts — 30 Mar 2006 @ 12:26 PM

  118. This is with respect to comment #108 and the discussion that ensued.

    My very brief and only response here will be strictly limited to those addressed on my 2 papers (Chelliah and Bell, 2004 and Bell and Chelliah, 2006) with Gerry. Anybody can use anything to support any position. That’s not my call. I can only defend for myself and the science in my papers and what is claimed there.

    Can anyone please tell me where the words “100 year cycle” or the “100 year oscillation” is used anywhere in our papers (Chelliah and Bell, 2004; Bell and Chelliah, 2006) and where we are suggesting such cycles and their implications. Can you please read the papers thoroughly before commenting on them in the public domain, particularly if those comments are very negative and are quite critical?

    Besides addressing other issues, the BC2006 paper has everything to do with an attempt to explain the observed overall increase in N.Atlantic hurricane activity since 1995 and how it could be linked to local and tropics-wide SST (see also CB2004), ENSO and other global climate conditions. These two papers together constitute the basis of NOAA’s long lead North Atlantic Hurricane outlooks issued since 1998 and the East Pacific’s Hurricane outlooks since 2002. The main thrust of the paper is to explain how the recent increase in North Atlantic Hurricane activity is quite possibly associated with the recent increase in SST in the Atlantic basin and in that sense how it is much different than similar higher levels of Hurricane activity observed in the 1950’s and 60’s.

    These papers have nothing to do with global warming or an explanation of the possible relationship between increase in the number of major hurricanes and increased SST values quite possibly associated with global warming.

    I am looking forward to answer fully all those questions on my paper from those who have taken the time to read it completely and thoroughly, but not here. The papers have been well peer reviewed; all major concerns of the anonymous reviewers satisfactorily addressed by us, and thus heavily scrutinized by competent scientists just as any of your papers are. Let’s have some respect for the American Meteorological Society and its ‘Journal of Climate’s peer review system. Please!

    Thanks for the opportunity.

    Comment by Muthuvel Chelliah — 30 Mar 2006 @ 4:10 PM

  119. Dr. Chelliah, as a nonscientist reader here, I appreciate _very_much_ your saying that much here. It’s appropriate! One repeated big lesson for us watching the experts here is — read the primary source, verify firsthand what’s claimed about anyone’s work to the extent we can understand it, and ask help.

    I hope wherever the further discussion happens, we nonexperts can read that eventually. It’s the best possible continued education about how this all works. Will your full papers available to the general public somewhere you can point us to?

    Gavin, the link you gave in #102 (and Ferdinand also in #115) the later abstract seems to be broken.

    [Response:It works for me… -gavin]

    Comment by Hank Roberts — 30 Mar 2006 @ 4:30 PM

  120. Re #116 (comment),

    Raypierre, I am a little surprised by your response.
    The discussion was about the warming of the tropical oceans, especially the part of the North Atlantic, where the Atlantic tropical cyclones are born, not about climate in general.

    The Chen/Wielicki papers point to the fact that there is a satellite derived increase in solar radiation at the surface (~2 W/m2) in the tropics since begin 1990’s.

    This is confirmed by later work from Pinker ea., which compares satellite data (~3 W/m2 increase in the tropics after 1990) with ground data (described in the full article) and is published on 6 May 2005, probably taken into account any previous detected errors in the satellite data.

    This parallels the “global dimming” trends from ground stations of Wild ea. with only one low-latitude station in the Atlantic: Bermuda, which shows a 5 W/m2 increase in all sky conditions, but none in cloud-free conditions, which points to a change in cloud cover.

    This parallels the changes in heat content of the oceans of Levitus ea., fig. 1. While there are no specific data given for individual areas, the 10N-30N ocean band of interest (fig. 2) shows the largest increase in heat content since 1955.

    These three independent data series are quite consistent with each other, but inconsistent with aerosol data, either for area as in time frame. And are inconsistent with GHG trends in magnitude and sign for (multi)decadal time frames (how do you explain the decrease 1980-1990 of ocean heat content with increasing GHGs and steady state SO2 emissions?).

    Thus of Chen/Wielicki, only the increase in insolation at ground level (SW in fig. 2 of Wielicki) is relevant here, the TOA budget, (which points to tropical atmospheric cooling?) is relevant for climate in general, but not (directly) for tropical ocean warming.

    And the problems of models with clouds go beyond the seasonal cycles, see the work of Allan and Slingo. Although mainly about outgoing LW radiation, this is related to cloud radiation properties/cover, see Fig.1.
    Further, climate models significantly don’t capture any natural cycles between 10-100 years, see Fig. S1 in the supporting on line material of Barnett ea.

    Thus in IMHO, that the recent ocean warming (specifically in the tropical Atlantic) is mainly of natural origin still stands. But if I am wrong (based on better data), I have no problems to accept that (and will not reuse these arguments).

    Comment by Ferdinand Engelbeen — 30 Mar 2006 @ 8:33 PM

  121. Re #118: The picture begins to clarify a little. Of course researchers should be left alone to do their work, but unfortunately it appears that NOAA has intentionally mischaracterized and continues to mischaracterize the Bell and Chelliah work as supportive of the position stated by the NOAA PR flack in the newspaper article (pasted below) from last Sunday’s Providence (RI) Journal. B+C aren’t named, but I’m not aware of any other work that could be the basis for the position. As stated in the now-infamous NOAA statement on hurricanes from last fall:

    “Research by NOAA scientists Gerry Bell and Muthuvel Chelliah, currently in press with the Journal of Climate, describes the tropical multi-decadal signal and shows that it accounts for the entire inter-related set of conditions that controls hurricane activity for decades at a time. Their study also shows that the tropical multi-decadal signal is causing the observed multi-decadal fluctuations in Atlantic hurricane activity since 1950.”

    So apparently some liberties were taken by whoever approved the contents of that page (presumably Max Mayfield or someone higher up). As well, it appears that the NOAA gag order continues in place, albeit less officially than before.

    —————————————-

    NOAA hiding truth about hurricanes, scientists say

    The national agency is accused of fudging data and censoring top scientists who link hurricane intensity with global warming.

    01:00 AM EST on Sunday, March 26, 2006
    BY PETER B. LORD
    Journal Environment Writer

    Hurricanes are getting worse because of global warming.

    Kerry Emanuel, a veteran climate researcher at the Massachusetts Institute of Technology, made that assertion to a roomful of University of Rhode Island scientists a few months ago. He also charged the federal government’s top science agency with ignoring the growing research making that link.

    Instead of telling the public the truth, he said, National Oceanic & Atmospheric Administration officials are insisting that hurricanes are worse because of a natural cycle.

    Emanuel’s comments made little impact at the time. But during the last three months, his comments and those of other scientists have become like hurricanes — more frequent and more severe. Finally, they are reaching the public.

    James E. Hansen, the top climate scientist at the National Aeronautics and Space Administration, was quoted in The New York Times in January as saying he had been threatened with “dire consequences” by some NASA political appointees if he continued to call for limits on emissions of gases linked to global warming.

    Many climate scientists at the NOAA may no longer take calls from reporters, the story went on to say, unless the interview is approved by administration officials in Washington, D.C., and is conducted with a public-affairs officer present. But where scientists’ views on climate change align with those of the administration, The Times said, there are few restrictions on speaking or writing.

    In February, New Republic magazine published a story about the NOAA’s insistence both in news conferences and on its Web site that global warming has no effect on hurricanes.

    Many respected climate scientists, including some working at the NOAA, believe that is wrong, according to the article. It quoted Don Kennedy, editor in chief of Science magazine, as saying, “There are a lot of scientists there who know it is nonsense . . . but they are being discouraged from talking to the press about it.”

    Last month, retired Navy Vice Adm. Conrad C. Lautenbacher Jr., the NOAA’s administrator, issued a statement saying that the media reports about muzzling NOAA scientists are incorrect. He urged the NOAA’s scientists to speak freely and openly.

    He was almost immediately contradicted by Jerry Mahlman, a former director of one of the NOAA’s top laboratories in New Jersey, who said climate scientists at the NOAA have, “indeed, recently been systematically prevented from speaking freely to anyone outside NOAA” about “our inexorably warming planet.”

    Finally, NASA’s Jim Hansen appeared on 60 Minutes last Sunday night and repeated his story of government censorship. The story also introduced Rick Piltz, who resigned from the U.S. Climate Change Science Program last year because, he said, the White House kept softening his annual reports on climate change.

    When Emanuel raised his criticisms of the NOAA in December, the worst hurricane season in modern history had just ended, and it had broken records set by the 2004 season.

    Worsening storms are no coincidence, Emanuel said. They are feeding off ever-warming ocean waters.

    Emanuel said in passing that the NOAA, the nation’s leading science agency — home of the National Weather Service and the National Hurricane Center — was telling the wrong story.

    “NOAA talks about natural cycles, but there is no evidence this is cyclic,” Emanuel said.

    Despite growing scientific evidence that global warming is making hurricanes more frequent and more severe, Emanuel said the NOAA has adopted the stance that there is no global-warming effect on hurricanes.

    This was not the first time for such accusations. Two years ago, 60 of the country’s leading scientists had signed a statement calling for an end to the “distortion of scientific knowledge for partisan political ends” by the Bush administration.

    The scientists charged that, to support President Bush’s decision not to regulate emissions that cause climate change, the administration has “consistently misrepresented” findings by government scientists. They also found the administration had been working to undermine government science used to deal with childhood lead poisoning, endangered species, air pollution and environmental-health issues. Since then, more than 8,000 other scientists have signed on.

    Emanuel said new stories of scientific censorship emerged at a meeting with NOAA scientists last fall.

    “Scientists at NOAA have been told there is a gag order on [discussing the impact of] global warming,” Emanuel said. “A U.S. government organization should not have a gag order on science. Even in Cuba, scientists can’t talk about politics, but they can say anything they want about science.”

    SOON AFTER Emanuel’s appearance at URI to discuss his research and his new book, Divine Wind: The History of Science and Hurricanes, The Providence Journal sought to test his conclusions.

    The first call was to Isaac Held, a senior research scientist at the NOAA’s prestigious Geophysical Fluids Laboratory, in Princeton, N.J. It was there, last fall, that Emanuel said he first heard about NOAA censorship. Held said he hadn’t been affected, but he advised calling Thomas Knutson, a NOAA scientist whose research showed a link between climate change and hurricane intensity.

    “Stick to hurricanes. Talk to Tom,” Held advised.

    Knutson wouldn’t talk.

    “When we’re contacted by reporters, we have to have clearance before we can speak about issues. This is NOAA’s media policy,” Knutson said. He suggested calling Jana Goldman, in NOAA’s public-affairs office.

    Is this a new policy? he was asked.

    “Check with her,” Knutson said. “I’m not sure when the policy was implemented.”

    Calls to NOAA’s public-affairs office led to Kent Laborde, who was described as the public-affairs person who focuses on climate-change issues.

    Laborde made it clear that the NOAA has discounted the research tying global warming to worsening hurricanes.

    “What we’ve found is, if you look at a couple segments of science, observational or modeling, there is no illustrated link between climate change and hurricane intensity,” Laborde said. “We actually have periods of intensity followed by periods of lower intensity. We have evidence of periods going back to the 1930s. It follows a clear pattern.”

    Laborde was asked if he would approve an interview with Knutson.

    What is the topic? he asked.

    Emanuel’s theories linking climate change to worsening hurricanes.

    “Chris Landsea would be better. He’s an observational scientist,” Laborde said.

    Landsea is a top meteorologist at the NOAA, often called upon for expert testimony to Congress or to speak at news conferences. He also very publicly quit an international climate-change panel last year, because one of its leaders had publicly linked global warming to hurricane severity.

    At Laborde’s request, Landsea cheerfully discounted Emanuel’s theories in an interview with The Journal.

    Landsea says he believes what we are really experiencing is a return to an active period of hurricanes, similar to what happened in the late 1940s to the 1960s.

    He argued that Knutson’s research reflects only a small link between global warming and hurricane intensity.

    As for Emanuel’s work, Landsea said, “My opinion is his study is very unconvincing.”

    Landsea insisted that, although he represents the NOAA, there is no official NOAA stance on the impact of global warming on hurricanes.

    “There are different scientists with different points of view,” He said. “Talk to people at Princeton. Tom Knutson has different opinions than I. But he’s allowed to speak.

    EMANUEL SAID he has no problem with engaging in a scientific debate. What concerns him, he said, is that the NOAA seems to be ignoring the debate, and has come down on just one side.

    At the annual convention of the American Geophysical Union last December in San Francisco, a conference that draws 11,000 scientists, Emanuel said he chided the NOAA’s restrictions during a scientific presentation — and was greeted with a standing ovation.

    “The intensity and frequency of storms are increasing,” Emanuel said. “And that is almost certainly because of global warming. There is no evidence of ‘natural cycles.’ ”

    More work needs to be done, he said. But the NOAA should at least acknowledge the theory.

    “There are lots of pieces of evidence, like in a trial,” Emanuel said. “All point in a certain direction. I think the evidence is really decisive. And most of my colleagues agree.”

    The Government Accountability Project, a nonprofit organization that supports federal whistleblowers, last week announced that it is sponsoring the watchdog organization Piltz had created after leaving his government post last summer.

    The new organization, Climate Science Watch (at http://www.climatesciencewatch.org), reports on political meddling on government climate-change research.

    Piltz said he resigned because his annual climate-change reports were repeatedly watered down by an administration staff lawyer who previously had worked as an energy-industry lobbyist. Piltz said he is well aware that NOAA policies “require political preapproval on all science contacts with the media.”

    “If this administration had a different reputation — respect for science — we wouldn’t be so upset,” he said.

    “I’m all for honest exchanges, but we’ve got science and politics co-mingled here,” Piltz said. “What happens when the world of science collides with the world of politics? I know that world.”

    The NOAA’s actions are often subtle, he said, “but they reflect a pervasive pattern of deflecting the public’s attention and manipulating the way science is presented to the public.”

    “Federal scientists should be able to communicate with the public,” Piltz said. “Especially if it is about an important issue. We are paying for this stuff.”

    Last week, Emanuel said he had noticed one change at the NOAA since he made his complaints public, but it’s a small one, and it appears only in a footnote in tiny print at the end of the page. It is, he said, “a little disingenuous.”

    NOAA Magazine, an online publication, had carried a story at the end of November that wrapped up the terrible 2005 hurricane season. Its headline; “NOAA Attributes Recent Increase in Hurricane Activity to Naturally Occurring Multi-Decadal Climate Variability.”

    Last month, in small print at the end of the 12-page report, this editor’s note had been added: “The consensus in this on-line magazine story represents the views of some NOAA hurricane researchers and forecasters, but does not necessarily represent the views of all NOAA scientists. It was not the intention of this article to discount the presence of a human-induced global warming element or to attempt to claim that such an element is not present. There is a robust, on-going discussion on hurricanes and climate change with NOAA and the scientific community.”

    The note says the headline should have read: “Agreement Among Some NOAA Hurricane Researchers and Forecasters.”

    plord@projo.com / (401) 277-8036

    Comment by Steve Bloom — 30 Mar 2006 @ 10:20 PM

  122. Gavin, is the abstract only for subscribers? Maybe my character encoding is garbling it. I’ll fiddle with it.

    Comment by Hank Roberts — 30 Mar 2006 @ 10:55 PM

  123. Re #122: Hank, I can see it too, but anyway it seems appropriate to just post the text:

    Interannual and multidecadal extremes in Atlantic hurricane activity are shown to result from a coherent and interrelated set of atmospheric and oceanic conditions associated with three leading modes of climate variability in the Tropics. All three modes are related to fluctuations in tropical convection, with two representing the leading multidecadal modes of convective rainfall variability, and one representing the leading interannual mode (ENSO).

    The tropical multidecadal modes are shown to link known fluctuations in Atlantic hurricane activity, West African monsoon rainfall, and Atlantic sea surface temperatures, to the Tropics-wide climate variability. These modes also capture an eastâ??west seesaw in anomalous convection between the West African monsoon region and the Amazon basin, which helps to account for the interhemispheric symmetry of the 200-hPa streamfunction anomalies across the Atlantic Ocean and Africa, the 200-hPa divergent wind anomalies, and both the structure and spatial scale of the low-level tropical wind anomalies, associated with multidecadal extremes in Atlantic hurricane activity.

    While there are many similarities between the 1950â??69 and 1995â??2004 periods of above-normal Atlantic hurricane activity, important differences in the tropical climate are also identified, which indicates that the above-normal activity since 1995 does not reflect an exact return to conditions seen during the 1950sâ??60s. In particular, the period 1950â??69 shows a strong link to the leading tropical multidecadal mode (TMM), whereas the 1995â??2002 period is associated with a sharp increase in amplitude of the second leading tropical multidecadal mode (TMM2). These differences include a very strong West African monsoon circulation and near-average sea surface temperatures across the central tropical Atlantic during 1950â??69, compared with a modestly enhanced West African monsoon and exceptionally warm Atlantic sea surface temperatures during 1995â??2004.

    It is shown that the ENSO teleconnections and impacts on Atlantic hurricane activity can be substantially masked or accentuated by the leading multidecadal modes. This leads to the important result that these modes provide a substantially more complete view of the climate control over Atlantic hurricane activity during individual seasons than is afforded by ENSO alone. This result applies to understanding differences in the â??apparentâ?? ENSO teleconnections not only between the above- and below-normal hurricane decades, but also between the two sets of above-normal hurricane decades.

    Comment by Steve Bloom — 30 Mar 2006 @ 11:34 PM

  124. Now this is interesting. It turns out that the disclaimer added to the bottom of the NOAA magazine article reads as follows:

    *EDITOR’S NOTE: This consensus in this on-line magazine story represents the views of some NOAA hurricane researchers and forecasters, but does not necessarily represent the views of all NOAA scientists. It was not the intention of this article to discount the presence of a human-induced global warming element or to attempt to claim that such an element is not present. There is a robust, on-going discussion on hurricanes and climate change within NOAA and the scientific community.

    ‘The headline and paragraph could have more clearly stated:

    ‘”Agreement Among Some NOAA Hurricane Researchers and Forecasters”

    ‘There is agreement among a number of NOAA hurricane researchers and forecasters that recent increases in hurricane activity are primarily the result of natural fluctuations in the tropical climate system known as the tropical multi-decadal signal.â??

    ‘Reference: Goldenberg, Stanley B., Christopher W. Landsea, Alberto M. Mestas-Nunez, William M. Gray. July 20, 2001. The Recent Increase in Atlantic Hurricane Activity: Causes and Implications. Science, Vol. 293. no. 5529, pp. 474 – 479.’

    The detail I had missed is that the reference for this statement very pointedly was not any of the Bell and Chelliah work, but rather an old (as these things go) Science paper. The abstract reads:

    “The years 1995 to 2000 experienced the highest level of North Atlantic hurricane activity in the reliable record. Compared with the generally low activity of the previous 24 years (1971 to 1994), the past 6 years have seen a doubling of overall activity for the whole basin, a 2.5-fold increase in major hurricanes (50 meters per second), and a fivefold increase in hurricanes affecting the Caribbean. The greater activity results from simultaneous increases in North Atlantic sea-surface temperatures and decreases in vertical wind shear. Because these changes exhibit a multidecadal time scale, the present high level of hurricane activity is likely to persist for an additional ~10 to 40 years. The shift in climate calls for a reevaluation of preparedness and mitigation strategies.”

    The paragraph relating to global warming reads:

    “One may ask whether the increase in activity since 1995 is due to anthropogenic global warming. The historical multidecadal-scale variability in Atlantic hurricane activity is much greater than what would be “expected” from a gradual temperature increase attributed to global warming (5). There have been various studies investigating the potential effect of long-term global warming on the number and strength of Atlantic-basin hurricanes. The results are inconclusive (48). Some studies document an increase in activity while others suggest a decrease (49). Tropical North Atlantic SST has exhibited a warming trend of ~0.3°C over the last 100 years (38); whereas Atlantic hurricane activity has not exhibited trendlike variability, but rather distinct multidecadal cycles as documented here and elsewhere (12, 13, 17). The extreme activity in 1995 has been attributed in part to the record-warm temperatures in the North Atlantic (25). The possibility exists that the unprecedented activity since 1995 is the result of a combination of the multidecadal-scale changes in Atlantic SSTs (and vertical shear) along with the additional increase in SSTs resulting from the long-term warming trend. It is, however, equally possible that the current active period (1995-2000) only appears more active than the previous active period (1926-1970) due to the better observational network now in place. During the previous active period, only 1966-1970 had continual satellite coverage (33, 50). Further study is essential to separate any actual increase from an apparent one due to more complete observations.”

    So even this referenced paper doesn’t strictly support the disclaimer’s assertion that “recent increases in hurricane activity are primarily the result of natural fluctuations.” What research does?

    Comment by Steve Bloom — 31 Mar 2006 @ 12:00 AM

  125. OK, I can see the abstract now too.

    Per Dr. Chelliah’s request in #118, as one who can’t read and understand the full papers, I’ll wait and hope more appears here after those discussions elsewhere, and thank Dr. C. again for saying that much.

    I did find Dr. C’s words in #118 helpful stating clearly both what “The main thrust of the paper is” and what “These papers have nothing to do with.” I commend those clear statements to others, while we wait. They limit the claims others could make about what’s proved by them, narrowly and precisely.

    Comment by Hank Roberts — 31 Mar 2006 @ 12:33 AM

  126. Re 108 and comments

    The problem of rather speculative oscillations reminds me on something I have mentionned before but got no reaction. I see also some trouble with the AMO, which is claimed to be responsible for the SST increase in the Atlantic and the corresponding increase in hurricanes. I’ve put now some graphs on the web for illustration:
    http://www.proclim.ch/products/misc/amopictures.html

    1. The AMO, which corresponds to the detrended North Atlantic SSTs, looks very similar to the detrended global surface temperature (DGT, see graphs). It has a very similar amplitude and a very similar period length and very similar patterns. The AMO looks very much like the regional expression of the global temperature evolution. And the very nice “pseudo oscillation” of the DGT is most probably not the result of a physical oscillation but the accidental result of the superposition of different non-regular forcings (solar, volcanoes, aerosols, GHG’s).
    It is very unlikely that the AMO determines the multidecadal variability of the global temperature so strongly, because the amplitude of the AMO, which represents only a small part of the globe, would be clearly dampened in the global signal. Since the amplitudes are similiar, it is much more likely that the AMO represents a result of the global signal.

    2. Looking at a reconstruction of the AMO back to 1600 by Gray et al. 2004 (see graphs), it is very hard to find any apparent regularity which would assist the idea of an oscillation. You can find many possible oscillation frequencies (200 years, 100 years, or less…), but none of them is really apparent. The only one which seems to emerge somewhat is at about 100 years, and not 70 as in the 20th century…

    3. The only physical explanation for an AMO presented until now is the fact, that some models produce oscillations in the order of 100 year periods due to THC variations. However, given the variability of the period lengths in relation to the limited number of periods to compare (only a few, only 2 measured), this “correlation” seems rather speculative. I haven’t seen a simulation yet which fits nearly as well as the global temperature…

    If the AMO would really only be the result of global temperature evolution (with some additional regional signals, of course), this would mean that the recent increase in Atlantic hurricane activity is strongly linked to global warming…

    To be discussed…
    Urs

    [Response: Thanks. Your points are very well taken. – gavin]

    Comment by Urs Neu — 31 Mar 2006 @ 9:35 AM

  127. Re #s 118 and 121 (first two paragraphs): Just to clarify in case anyone is still reading this, after going back and double-checking the source material it became clear that Bell has been out (primarily last fall) making statements in support of the official NOAA “all natural cycle” hurricane hypothesis while Chelliah has not. Of course co-authors are entitled to interpret their joint work in defferent ways, but it remains interesting that only those at NOAA who agree with the official agency position have spoken to the press.

    Speaking of NOAA, this coral bleaching story from two days ago features yet another NOAA representative denying the impact of GW while other scientists speak out.

    Then there’s this story about the increasing effects of acidification in the Pacific, although in this case the NOAA scientist is simply silent on the GW connection while others discuss it.

    Comment by Steve Bloom — 1 Apr 2006 @ 8:05 PM

  128. re 85.

    Another flip of the coin turns up heads on the Red River. Is this more bad luck or just another global warming fingerprint? Are more frequent and larger winter-spring rainfall driven Red River floods part of polar/upper latitude amplification of the hydrologic cycle?

    GF/EGF: Red tops its banks
    Apr. 01, 2006
    http://www.grandforks.com/mld/grandforks/14238344.htm

    Excerpts:

    The river could hit “major” flood stage 46 feet or higher by next
    week, according to the National Weather Service forecast office in
    Grand Forks. That would be the highest the river has been since the
    Flood of 1997. …

    The highest crest since 1997 was 45 feet in the spring of 2001.

    See also: Historical Peak Streamflow
    USGS 05082500 RED RIVER OF THE NORTH AT GRAND FORKS, ND
    http://nwis.waterdata.usgs.gov/mn/nwis/peak/?site_no=05082500&agency_cd=USGS

    Comment by Pat Neuman — 1 Apr 2006 @ 10:27 PM

  129. With reference to Dr. Cheliah’s response (# 109), he is quite correct. Cheliah and Bell do not in either of their papers (and I have read both in great detail) refer to a “cycle” or “an oscillation” of a 100-year period. But they do refer to a “mode” of 50 years with one minimum and one maximum. They note that the “mode” changes sign (between the minimum in the 1950s to the maximum late 1990s) at the time of the global changes in general circulation character commented on by many in the past and therefore. But how can one differentiate between the C&B mode and a trend? Why was tghe dat not detrended prior to the analysis? Why was the possibility that the “mode” may be a trend and one associated with GW not be mentioned? These are the questions I ask.

    Dr. Cheliah makes the point that the two papers were not intended to discuss global warming and hurricanes. But others in high places in NOAA have used these articles as evidence that the changes that we have seen over the last few decades and espacially in the Atlantic in the last 11 years are just natural variations of the climate system with the inference that we understand what these cycles are, how they come about and what they will do in the future. I recognize that one cannot be responsible for what use someone else makes of a paper one writes but ir would seem to me that with a little thought where one says “mode” that “mode or trend” could have projected a neutral stance for the paper.

    I am sorry that Dr. Cheliah has taken umbrage at my comments. They were not menat to be personal nor were they meant in disrespect to the American Meteorology Society’s J. Clim. review process. (God forbid, I publish there a lot too so how could I argue that the review process is nothing less than exemplary (a joke!)) I applaude C&B for publishing their work and avoiding what many in the hurricane-global warming discussion have done: criticize through commentary and not thorugh the peer-reviewed process. In fact, one could raise an eyebrow becasue that is probably what I have done here. Apologies! But because something is published does not mean it is correct. Not even the AMS is that clairvoyant. The scientific method stipulates that all work should be examined carefully and commented on critically. C&B and other scientists will build upon what is said in the two papers or modify conclusions accordingly. That is the way we move ahead. I just happen to query the suitability of the C&B statistics and what one can infer or cannot infer from the methods they have used. We will continue our examination and publish a response in due course. PW

    Comment by Peter Webster — 2 Apr 2006 @ 11:46 AM

  130. Re #126:

    Urs and Gavin,

    While there may be some similarity between global temperatures and the AMO, the effects of the AMO can be seen on longer time scales than the recent upswing in temperatures.
    – there is a 70-80 year oscillation in European-wide summer temperatures visible, based on the longest instrumental records, combined with tree rings. See Shabalova and Weber
    – the AMO not only is connected to temperature (and precipitation) variations in Europe, but also precipitation in the USA and Middle-East/Africa, thus may be seen in overall NH and global climate. See Sutton and Hodson.

    But IF the detrended AMO correlates well with the detrended global temperature change, and IF tree rings are good indicators of past climate, the AMO can be used as a proxy for pre-instrumental temperature variations, which indicate a (totally natural) variation of up to 0.6 degr.C 1570-1850 (see Betancourt ea., page 27, but the other pages are interesting too), larger than the variation in the 20th century, which still is 0.4 degr.C (page 23). That besides the influence of the increased solar strength in the first halve of the past century on the SST trend… Thus it is rather speculative to blame today’s higher Atlantic SST’s mainly on GHGs…

    Btw, I only have an empty page when opening the link to the ProClim AMO graphs.

    Comment by Ferdinand Engelbeen — 2 Apr 2006 @ 5:50 PM

  131. Re 130

    Ferdinand, since the AMO is correlated to global temperature variations, any regional climate signal which is in some way correlated to global temperature (and there is quite a number of them), will also be correlated to the AMO. Thus it is no surprise that you will find an ‘influence’ in the whole Northern Hemisphere and in global climate. A global response of the AMO in fact supports the suggestion that the AMO more or less represents the global temperature and maybe nothing else. Where is the evidence that the signals you mention are influenced by the AMO and not just by the global signal?

    And where is the evidence that the AMO is a regular signal? Just the one complete period we have in the measured data?
    If you look at the Betancourt graph (meanwhile published in Gray et al. 2004, ref. see below), you find negative peaks roughly 120,100,100, and 70 years apart, and positive peaks roughly 110, 100, 90, and 60 years apart. And there might be a 250 year cycle superposed, and there is a huge signal before 1600 out of order anyway, etc. I can’t see any regular signal at all. The 60-80 year ‘oscillation’ you only can find since 1870 where the measurements start.

    Btw, I don’t see a reason to use a tree-ring derived AMO reconstruction for the NH temperature, if we have NH temperature reconstructions which include more tree-rings and additional data. You do not gain anything, do you?

    Gray, S. T., J. L. Graumlich, J. L. Betancourt, and G. T. Pederson, 2004: A tree-ring based reconstruction of the Atlantic Multidecadal Oscillation since 1567 A.D. Geophys. Res. Lett., 31, L12205, doi:10.1029/2004GL019932

    I don’t know why you can’t see the graphs on our page, I’m sorry. It shows the AMO from Knight et al. 2005 and the reconstructed AMO from Gray et al. 2004 (similar to Betancourt). The detrended global temperature from CRU-data you easily can calculate yourself.

    Comment by Urs Neu — 3 Apr 2006 @ 6:05 AM

  132. Re #131

    Urs, sorry for the late reply, we are just in the (hopefully!) last phase of in-house renewal…

    The AMO is the result of detrended Atlantic SST’s, thus it is quite normal to use tree rings along the Atlantic coast to reconstruct the AMO before the instrumental era. Although there may be better proxies (sediments?) than tree rings (which are influenced by many other items than temperature alone), there is more variability in the AMO tree ring reconstruction than in the MBH98/99 NH reconstruction, but less than for other NH reconstructions (like the Esper all tree ring reconstruction), thus the link between AMO and NH/global temperatures in amplitude is not so sure.

    And is it not the opposite, that Atlantic Ocean heat content/SSTs are influencing the whole NH climate?

    Further, the variations in Atlantic (and general tropical) ocean heat content are much too large to be caused by aerosol/GHG combinations. Even the timing is not consistent with the increase in aerosols (1945-1975) or GHGs (mainly after 1945 until current) for ocean heat content (decreasing 1980-1990!).

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