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Gray and Muddy Thinking about Global Warming

Filed under: — group @ 26 April 2006

Anybody who has followed press reporting on global warming, and particularly on its effects on hurricanes, has surely encountered various contrarian pronouncements by William Gray, of Colorado State University. A meeting paper that Gray provided in advance of the 2006 27th Conference on Hurricanes and Tropical Meteorology (taking place this week in Monterey California, and covered here by CNN), provides an illuminating window into Gray’s thinking on the subject. Our discussion is not a point-by-point rebuttal of Gray’s claims; there is far more wrong with the paper than we have the patience to detail. Gray will have plenty of opportunities to hear more about the work’s shortcomings if it is ever subjected to the rigors of peer review. Here we will only highlight a few key points which illustrate the fundamental misconceptions on the physics of climate that underlie most of Gray’s pronouncements on climate change and its causes.

Gray’s paper begins with a quote from Senator Inhofe calling global warming a hoax perpetrated on the American people, and ends with a quote by a representive of the Society of Petroleum Geologists stating that Crichton’s State of Fear has "the absolute ring of truth." It is the gaping flaws in the scientific argument sandwiched between these two statements that are our major concern.

Claim: The Thermohaline Circulation causes Global Warming, Hurricane Cycles, etc

For years, perhaps decades, Gray has been ascribing all sorts of climate changes and hurricane cycles to fluctuations in the Thermohaline Circulation (THC), an overturning circulation in the Atlantic ocean associated with formation of deep water in the North Atlantic. None of the assertions are based on rigorous statistical associations, oceanographic observations or physically based simulations; it is all seat-of -the-pants stuff of a sort that was common in the early days of climate studies, but which is difficult to evaluate when viewed as a scientific hypothesis. The THC is undoubtedly important to climate, because it transports heat from one place to another. However it cannot do magical things. It cannot created energy out of thin air (or thick water), nor can it make energy mysteriously disappear. Thus, Gray’s statement that "The average THC circulation cools the ocean by about 3 W/m2" is a scientific absurdity. In the paper Gray makes many extravagant claims about how supposed changes in the THC accounted for various 20th century climate changes ("I judge our present global ocean circulation conditions to be similar to that of the period of the early 1940s when the globe had shown great warming since 1910, and there was concern as to whether this 1910-1940 global warming would continue. But beginning about 15 years following the onset of a strong THC circulation in 1926, in the early 1940s, the warming began to abate. A weak global cooling began from the mid-1940s to the mid-1970s.") but the reader would never guess that he in fact has no direct oceanographic evidence that the THC was doing anything of the sort. These are all subjective estimates based on Gray’s conception of the relation of Atlantic temperatures to the THC state. In fact, it is exceedingly difficult to directly monitor the THC, and reliable results have only recently been obtained. We have reported recently on the "Decrease in Atlantic Circulation". For years prior to the publication of evidence that the THC was slowing down, Gray was testifying in Congress and writing widely that hurricane increases were due to Atlantic warming arising from a speed-up of the THC (see our article for some typical quotes). Confronted with evidence that the THC was in fact behaving in the opposite way to what he had been assuming, Gray did a flip-flop and came up with a new story that yields the same conclusions. There’s no shame in a scientist changing his or her mind, or in seeking new theories in the face of new observations. However, if Gray’s old theory was really testable, where were the tests to show that it was wrong in the years he was touting it? How is one to put any confidence in the new theory? The fact is that neither of Gray’s story lines about the THC is sufficiently well formulated to allow any clear-cut test. Nonetheless, insofar as it can be understood at all, some aspects of Gray’s new story line about the THC are demonstrably wrong.

The heart of the problem with Gray’s new version of the THC story is that he labors under the misconception that the THC primarily upwells in the tropics, so that any reduction in the THC cools the North Atlantic but warms the tropics. This conception is at least 50 years out of date. The tropical upwelling is a shallow wind-driven cell that does not connect to the THC. It is almost impossible for cold deep water to upwell in the tropics, because it takes too much energy to bring it up; the main THC connection is with the Southern Ocean, as described by Marotzke and references therein (for more general background, see also There are only a few very limited regions where moderately deep water can upwell in the Tropics. Simulations by Vellinga and Wood (Climatic Change, 2002) in fact show that a THC shutdown causes a cooling right into the Northern Subtropical Atlantic (the birthplace of hurricanes), and in fact only very weak warming in a few spots elsewhere in the tropics. On a longer time scale, the classic study of Manabe and Stouffer (Paleoceanography 1997) shows virtually no impact of THC shutdown in the tropics, but a considerable remote impact in the Southern Ocean. No doubt, Gray would object that these are only models, but why should we believe that Gray’s drawing of circles and arrows on a map yields a better prediction than a simulation embodying the best of what we know about the underlying physics?

Note that Gray does not merely claim that THC changes are responsible for the observed hurricane cycles. He in fact claims that the entire 20th century warming signal is due to a slowdown of the THC, and that CO2 has nothing to do with it. He claims flatly and without supporting evidence that models cannot simulate the THC properly, neglecting the fact that the models employed in the IPCC reports yield a rather wide variety of different possible THC behaviors, and none of them, including ones known to have a sensitive THC, spontaneously generate a warming of the sort Gray claims. Insofar as we can follow Gray’s reasoning, he appears to think of the THC as burying heat in the deep ocean, as if the heat were some kind of solid nuclear waste. Thus, weak THC = less heat removal = warming, in Gray’s world view. In reality, everything known about the physics of the THC’s effect on climate suggests the opposite. For example, Vellinga and Wood find that, owing to certain nonlinearities like sea ice formation, a shutdown of the THC leads to a reduction in the Northern Hemisphere mean temperature, and very little multidecadal scale effect on the Southern Hemisphere mean temperature.

The other reasons Gray thinks that the THC could cause global warming are tied up with a number of additional misconceptions he has about the physics of climate.

Claim: Evaporation changes cause global warming, hurricane cycles, etc.

Gray’s grand answer to the riddle of global warming is evaporation, presumably modulated by changes in the THC. Again, Gray simply doesn’t seem to understand energy conservation. Evaporation does not create heat; it does not add any heat to the climate system or take it away. It is an energy transfer that moves heat from a moist surface (like the ocean’s) into the atmosphere. That severely constrains what evaporation changes can do to climate. In contrast, changes in CO2 concentration affect the top of atmosphere radiation budget directly, and change the rate at which the whole climate system loses energy.

Let’s start with an atmosphere that is in equilibrium, both at the surface and top-of-atmosphere. Now reduce the evaporation (you could do it by reducing the surface wind). The surface is now receiving more energy than it loses, so it will begin to warm. However, the atmosphere is no longer receiving all the energy it used to obtain from the surface as evaporative heat transfer; hence the atmosphere will begin to cool. This adjustment will continue until balance is restored. The precise way the adjustment is divvied up between atmospheric cooling and surface warming depends on details like the net atmospheric infrared opacity, boundary layer relative humidity,and so forth. However that all shakes out, the net result is nothing at all like the observed pattern of warming, in which both troposphere and surface warm up. This reasoning can be confirmed in the simplest radiative-convective model, of the sort introduced by Manabe and Strickler in the 1960’s.

A more serious problem is that Gray doesn’t even understand that the greenhouse effect works primarily through the effect of greenhouse gases on the top of atmosphere radiation budget, and only very indirectly through the surface budget (as explained in A busy week for water vapor). This compromises almost all of his analysis. For example, many of the supposed changes in surface budget he describes could in fact be due indirectly to changes in greenhouse gases, via their affect on low level atmospheric temperature. By balancing a 4 W/m2 (top of atmosphere) CO2 radiative forcing against changes in evaporation, Gray concludes that the warming from doubling CO2 would be a mere two tenths of a degree C.. He ascribes the weak warming to the lack of water vapor feedback in his calculation, but in fact it is simply due to an incorrect calculation of the energy balance. Standard radiative physics based on a correct treatment of the top-of-atmosphere balance– physics going back at least to Arrhenius– yields a surface warming of about 1C in response to a doubling of CO2, when water vapor feedback is neglected. Gray has committed the major blunder of applying that 4 W/m2 top of atmosphere forcing at the surface. In reality, when that radiative forcing is properly applied at the top of the atmosphere, it leads to a warming of the entire atmospheric column which, at the surface, yields a far larger perturbation in the surface energy budget, as we have explained in the above-referenced article.

By the way, Gray discounts water vapor feedback, based on what seems to be a gut feeling on weather systems, plus some unspecified analysis of the NCEP reanalysis dataset (which is completely unsuitable for studying trends in mid tropospheric water vapor); more reliable satellite based studies (e.g. Soden’s study described in A busy week for water vapor ) support a positive water vapor feedback, and even Lindzen seems to be no longer arguing against this feedback.

Claim: Ocean heat storage is inconsistent with CO2 as a cause of warming

Gray also made a mess of an attempt to analyze the mid-twentieth century ocean heat storage. "… the globe underwent a weak cooling between 1950 and 1975 during which CO2 amounts were rising and causing a continuous mean energy gain over this 25 year period of about 0.4 W/m2. If all of this energy went into an accumulation of temperature in the upper 100 m of the global oceans, we would see an upper mean 100 m global ocean temperature increase of 1.1oC. " We are not sure where Gray gets the 0.4 W/m2 radiative forcing figure; the total radiative forcing increase from pre-industrial times to 1975 would be more like .95 W/m2 and it is not a trivial matter to figure out how much to subtract from that to account for the part compensated by ocean warming before 1950; the CO2 radiative forcing increase between 1950 to 1975, on the other hand, would be only .45 W/m2 and the mean new forcing over the period would be about half that. Be that as it may, Gray has not even done the arithmetic right, since .4 W/m2 going into a 100m mixed layer having specific heat of 4200 J/kg and density of about 1000 kg/m3 would only yield a warming of .75C . That’s far from the worst flaw in his calculation, since his two biggest blunders are the neglect of the radiative cooling due to sulfate aerosols (known to be a critical factor in the period in question) and his neglect of the many links in the chain of physical effects needed to translate a top of atmosphere radiative imbalance to a change in net surface energy flux imbalance. In fact, the calculation has been done very carefully by Hansen and co-workers, taking all factors into consideration, and when compared with observations of ocean heat storage over a period long enough for the observed changes to be reliably assessed, models and observations agree extremely well (see this article and this article.).

Concluding remarks

The Wall Street Journal has insinuated that there is some ageism involved in the reaction to Gray’s work ("Hurricane debate shatters civility of weather science," by Valerie Bauerlein, Feb.2, 2006). The problem is not Gray’s age — we all revered Henry Stommel who did some of his finest work in his seventies. The problem is Gray’s failure to adapt to a modern era of meteorology, which demands hypotheses soundly grounded in quantitative and consistent physical formulations, not seat-of-the-pants flying. The WSJ also made much of the withdrawal of an invitation for Gray to join a debate on hurricane trends at an Atlanta tropical meteorology conference. We can’t speak for the organizers, but we find it easy to believe that their decision was guided more by the invalidity of Gray’s scientific reasoning than by any political or personal considerations.

144 Responses to “Gray and Muddy Thinking about Global Warming”

  1. 51
    Mike Russell says:

    The…er…liberal use of ad hom at some URLs is merely a marginalization tactic

    For the record: While I’ll certainly cop to using ad hom incorrectly, I’m not from a conservative think tank, and I’m not out to marginalize anyone. Quite the opposite. I’m a lay reader who comes to this site genuinely wanting to see refutations of bad science; I am genuinely curious about what’s happening with the environment, and I’m looking for science to sort out the spin.

    Instead, I was simply assured there was spin. Which — without the hard-science rebuttal of at least a few of that paper’s points, which I’m sure would be easy for the scientists on hand — feels rather annoyingly like spin itself.

  2. 52
    Hank Roberts says:

    Mike, my suggestion for a work flow for understanding the things you find stated: pick a point for which the author gives a source/footnote. (That’s why the Gray doc is messy, it doesn’t have any!)

    So start with something the author bothered to document for you. Look up the footnote (Google Scholar) and for new info. Decide you have something reasonably convincing to you as a non-expert, show your work done to understand as far as you got, and ask for a scientist to help you.

    Point is the broadsides, talk pieces, puff pieces, journalism, whatever all are just full of assertions but without any cite or source there’s nothing really there to respond to, the author originally has to commit to some actual information as a basis — a footnote/cite — before people can give you the helpful discussion you are looking for.

    It’s mostly smoke and mirrors and bafflegab and bullshit, by design, to keep people confused. Read the masters’ work, and look skeptically at what’s being put forth today:

    “A demand for scientific proof is always a formula for inaction and delay and usually the first reaction of the guilty â�¦ in fact scientific proof has never been, is not and should not be the basis for political and legal action”

    An example of (private) candour from a scientist at the tobacco company BAT 1. (S J Green 1980)

  3. 53
    pat neuman says:

    re 151

    Mike Russell, you wrote — without the hard-science rebuttal of at least a few of that paper’s points, …

    William Gray wrote … I judge our present global ocean circulation to be similar to that of the period of the early 1940s …


    It would not be hard to do a rebuttal on Gray’s judgment and statement that our present state of the ocean circulation to be similar to in the early 1940s, but how much time spent would be needed to get together enough evidence to show a hard-science rebuttal? Wasted time not spent on real science has costs.

    [Response: On the point of the hard science rebuttal, that’s not too difficult. We just wanted to keep the post from getting too terribly long. The fact is that we have very few ways of knowing what the THC was doing throughout the last century and Gray doesn’t cite any hard science to justify his particular picture. To see some of the difficulties of trying to infer the THC state from historical oceanographic data, see . There was also a paper by Wu et al (GRL 2004) which touches on similar things. Or perhaps I’m misinterpreting the comment re 51. Was the comment asking for a rebuttal of Gray on the THC or for a hard science rebuttal of the CEI piece? –raypierre]

  4. 54
    Grant says:

    Re: #51

    I’m a lay reader who comes to this site genuinely wanting to see refutations of bad science; I am genuinely curious about what’s happening with the environment, and I’m looking for science to sort out the spin.

    I’d say that’s a nice summary of one of the important purposes of this site.

    I agree with the sentiment of many, that there’s just too much garbage being spread around for us to clean it all up. Also, the RC staff are working very hard to keep us up to date, but they have very limited time (and, I think, use it rather well).

    So I’d encourage those who post here regularly to feel free to do some of the work. If a post (like Mike’s) raises questions about something, we can help by responding. And, we should stick to the very high standards set by the RC team. Be clear, correct, and give references (and links) wherever possible. That’s much more persuasive than simply saying that a particular piece is “garbage.”

    Mike, bear in mind that there *is* a lot of trash out there, and it’s just not possible to reply to it all. Also, bear in mind that although many of us are scientists, few of us are climate scientists, so we’re not able to respond with as much expertise as those who maintain the site.

  5. 55

    Some technical questions:

    If the THC decreases, what happens to the heat distribution from the equator to the poles? Even if there is no variation of heat inflow in the tropics, how is that redistributed (more evaporation, stronger winds due to larger temperature differences…)?

    Or is it the other way round, that (observed) changes in cloud cover result in more heat inflow in the tropics, which warms the Arctic due to more heat distributed to the poles, which results in a slow down of the THC?

    Or a combination, shifted in time, which results in a large scale cycle?

    [Response: Interesting and worthy questions. I’m not sure what “large scale cycle” you mean, since there is a lot of evidence for the THC responding to forcing changes like freshwater dumps, but little or no evidence that it can undergo spontaneous internally generated vacillations of significant amplitude. Leaving that aside, the answer to your question about the effect of THC on gradients is that the Atlantic THC is a global cell which has northward heat transport all the way from the Southern hemisphere to the N. Atlantic. In some sense, it tranpsorts heat “the wrong way” in the Southern hemisphere. As such, there isn’t a clear or simple connection to what the THC does to the pole-eq temperature gradient in the NH. Since many aspects of the THC take 1000 years or more to equilibrate, what kind of response you get depends on the time scale. For fairly short-term (a few decade) shutdowns like in Vellinga and Wood, what you dominantly see is a massive cooling in the Northern Hemisphere Atlantic, more or less right to the equator. The cooling is more pronounced at high latitudes, and the meridional temperature gradient is very significantly increased in the SST, but much less so in the atmosphere, since the net change in meridional heat transport in the THC is not so very large compared to the atmospheric heat transport. What you are dominantly seeing in these short term runs is the effect of a reduction of Northward drift of warm water in the NH Atlantic, perhaps amplified by sea ice effects. I don’t want to speculate about clouds and evaporation, or even changes in the wind pattern, because the possibilities are too complex to make a simple story, and I don’t have enough data from Vellinga and Wood to get a handle on why things are happening and what causes what. It’s an interesting research question. –raypierre]

  6. 56

    Re: #53 et al.

    For an interesting read about reconstructions of the THC during the past century or so, see Knight et al., (2005, A signiature of persistent natural themohaline cycles in observed climate, Geophysical Research Letters, doi:10.1029/2005GL024233). Their Figure 4c shows a reconstruction of the THC from 1880 to present which shows a strengthening from about 1920 to 1950, a sharp weakening from about 1950 to about 1970 and a strengthening again from 1970 to present. The strength in the late-1940s is similar to the present (year 2000) strength.

    For those interested, here is the complete abstract:

    Analyses of global climate from measurements dating back to the nineteenth century show an “Atlantic Multidecadal Oscillation” (AMO) as a leading large-scale pattern of multidecadal variability in surface temperature. Yet it is not possible to determine whether these fluctuations are genuinely oscillatory from the relatively short observational record alone. Using a 1400 year climate model calculation, we are able to simulate the observed pattern and amplitude of the AMO. The results imply the AMO is a genuine quasi-periodic cycle of internal climate variability persisting for many centuries, and is related to variability in the oceanic thermohaline circulation (THC). This relationship suggests we can attempt to reconstruct past THC changes, and we infer an increase in THC strength over the last 25 years. Potential predictability associated with the mode implies natural THC and AMO decreases over the next few decades independent of anthropogenic climate change.

    [Response: Chip, as you well know, the recent and past peak are only similar after the observations have been linearly detrended. Since there is no reason to believe that secular warming is linear in time, all bets are off once this has been done. This is why the authors indeed clearly state in the above abstract that “it is not possible to determine whether these fluctuations are genuinely oscillatory from the relatively short observational record alone.” But this has been much discussed before on this site, and if all you’re going to do is recycle old arguments, you should not expect your comments to make it through our filter (please re-read our comments policy). -mike]

  7. 57
    Joel Shore says:

    Re #32: Chip, you say “I think that you and I both know (or at least I thought I knew) that RealClimate serves a different purpose than World Climate Report. World Climate Report doesn’t hide the fact that it exists to support the notion ‘that climate change is a largely overblown issue and that the best expectation is modest change over the next 100 years,’ but I didn’t know that RealClimate had an agenda besides setting the science straight.”

    I find this an interesting admission on your part. While I knew that in practice this was the purpose of WCR, I thought that you guys would argue it the other way around…i.e., that you end up on the side of the idea that climate change is largely overblown just because that is the scientifically correct side in your view.

    However, am I to understand that in fact you exist just to argue that side regardless of the science? I.e., am I to think of you sort of like a defense lawyer whose job it is to defend his client even if pretty much everyone including you knows he is likely guilty (so that you cherry-pick just the scientific evidence that supports your view, for example)? Or, maybe you really think he is innocent but are not above challenging evidence that you know is probably really correct? I don’t mean to be insulting but am just trying to better understand how you and Patrick Michaels view yourselves exactly.

  8. 58
    pat neuman says:

    re 56.


    If the strength of the THC in the late-1940s is similar to present, then

    Why are global temperatures higher at present than they were in the 1940s?

    Why were annual temperatures in Alaska higher in 2005 than in the late-1940s?

    Why is the Jakobshavn glacier in Greenland is now moving towards the sea at the rate of 113 feet a year instead of the normal speed of one foot a year?

  9. 59
    Jan Rooth says:

    Re #56 (Chip Knappenberger)

    I’m getting mightily confused here. The quoted abstract says that “we infer an increase in THC strength over the last 25 years,” which corresponds to Dr. Gray’s old hypothesis of a stronger THC leading to warming of the tropical Atlantic and thus to more hurricane activity. But Dr. Gray has now reversed himself and hypothesizes instead that a weaker THC is what leads to warming in the tropics.

    Furthermore, it’s hard to glean from that abstract how it is that they “infer” the past changes in THC. If it is inferred from observed climate change, then the argument becomes circular as far as I can see.

  10. 60
    Steve Bloom says:

    Re #57: It’s probably worth noting again that WCR is a public relations effort of the coal industry. Chip doesn’t like to talk about that.

  11. 61
    Hank Roberts says:

    WCR is produced here:
    Chip K. is correct, this is an ‘advocacy science’ business.

    “New Hope’s scientists are accomplished public speakers who present testimony before Congress …. Nightline, Politically Incorrect, and Crossfire and … the Los Angeles Times, Washington Post, Washington Times, the Chicago Tribune, and many others.”
    “…our team of world-class scientists can offer your company or organization New Hope for our environmental future.

    ” New Hope’s international team of research scientists, data analysts, editors, and web publishers have devised, conducted, prepared, and published important research for both the public good and for private clients.
    “World Climate Report, our bi-weekly online publication, is the nation’s leading source of breaking news concerning the science and political science of global climate change.
    “New Hope’s research scientists have published extensively in the refereed scientific literature …, and they rank among the most highly regarded climatologists in their respective fields….”

    Other info is available:
    “WCR is sponsored by the Greening Earth Society, a Western Fuels Association project founded to spread the “good news” that global warming is benficial for the planet.”

  12. 62
    Steve Bloom says:

    This was linked in a prior RC post, but folks interested in the details of this stuff will want to have a look at Gray’s attack on Webster et al (2005) and the Webster team’s response at . Science declined to publish Gray’s comment.

  13. 63
    Steve Bloom says:

    Just to note that the ever-shifting cast of fossil fuel industry front groups has shifted again, with the result that the site (I think this was the “Greening Earth Society”) listed on the Exxon Secrets site Hank linked to above no longer works. Perhaps Chip would like to update date us with a current listing of WCR personnel and funding sources/amounts.

    [Response: The post on Gray was supposed to be an invitation to discuss various aspects of the way THC and evaporation could or couldn’t affect climate. Unfortunately one of the earlier posters, with a lot more push next by Chip, derailed the discussion into a bunch of accusations about the nature of RC’s editorial policies and how we choose the scientific topics we discuss. It’s gone on too long, and I certainly don’t want this to turn into a forum for discussing where WorldClimateReport’s funding comes from. That’s valuable and important to discuss somewhere, but RC isn’t the right place to discuss it. It’s not your fault — you didn’t start this diversion, Chip did (and in a moment of weakness, I took the bait, when I shouldn’t have) — but I’m asking everybody to find some other forum to discuss such things. I’d much rather be responding to questions like Ferdinand’s –raypierre]

    [Response: I second that. As much fun as this all appears to be, can I ask that the conversation move back to substantive issues? There are plenty of forums where this kind of stuff is hashed through – but there are very few where the focus is on the scientific issues themselves and maybe that’s worth preserving? – gavin]

  14. 64
    Jan Rooth says:

    The more I dig around, the more mystified I become as to what Gray’s current thinking is regarding the THC.

    The powerpoint presentation from his recent talk at the hurricane conference in Orlando is here.

    Slide 37 shows a representation of the THC which has most of the upwelling in the north Pacific and some in the equatorial Indian Ocean. This idea is outmoded. As Toggweiler and Key explain:

    It now appears that most, if not all, the
    deep water sinking in the North Atlantic upwells
    back to the surface in the Southern
    Ocean south of the Antarctic Circumpolar
    Current. The upwelling in this case seems to
    occur within the channel of open water that
    circles the globe in the latitude band of Drake
    Passage (55-65°S). Drake Passage lies within
    the belt of mid-latitude westerlies. The flow in
    the surface Ekman layer is directed northward
    and is divergent (upwelling favorable) within
    the channel. A key dynamical factor in this
    problem is the lack of meridional barriers in
    the upper 1500 m of the Drake Passage
    channel. Without meridional barriers, there
    can be no net geostrophically balanced flow
    into the channel above 1500 m to balance the
    northward flow in the surface Ekman layer.
    This means that the winds, in driving surface
    waters northward out of the open channel, tend
    to draw up old deep water to the surface from
    depths near 1500 m.

    In the same presentation, slide 40 appears to indicate that he thinks all the upwelling is taking place in the equatorial Indian and equatorial west Pacific. He also posits a connection between the strength of this upwelling and the frequency and strength of el Nino events.

    (these are essentially the same as Figures 1 & 2 in the meeting paper cited in the original post, so apparently his thinking has not changed in the last couple of months on this misconception)

    Slide 39 shows bar graphs portraying a correlation of a weak THC with low numbers of intense Atlantic storms, and strong THC with high numbers of intense Atlantic storms. Yet as pointed out above, he now claims the opposite relationship, albeit with a “10 to 15 year lag”.

    Now I could be wrong, but as I understood his reasoning in the past, it was that a strong THC means more transport of warm water north across the equatorial Atlantic and into the main development region for Atlantic hurricanes. But clearly that would not be subject to any significant time lag. Furthermore, I can’t reconcile slide 39 with this (apparently) new concept. So it seems his thinking has changed in the last couple of months with regard to this issue.

  15. 65
    Jan Rooth says:

    Sorry, I posted the wrong link for the Toggweiler and Ke paper.

    Here is the correct one. (pdf)

  16. 66
    S Molnar says:

    Re #62: This pretty much answers the question I asked in #41. Thanks (and sorry I failed to notice the link in the original posting).

  17. 67
    pat neuman says:


    Gray wrote … I judge our present global ocean circulation conditions to be similar to that of the period of the early 1940s when the globe had shown great warming since 1910, …

    Can Dr. Gray tell us what caused our 1930s dust bowl? How come we didn’t have a 1990s dustbowl?

  18. 68

    The most compelling language in disproving Dr Gray would be to present his faulty calculations in terms of mathematical equations. I know some cringe at them, but this universal language speaks volumes and I wonder if there can be a few examples from the text written by the RC group.

    News from NH Polar region with possible influence over coming hurricane season would be the very weak or non-existent stratospheric polar vortex over this winter just past. In contrast with 1997, when the vortex was huge, and number of tropical storms and hurricanes very few, could this lack of strong winds also be mimicked near the tropics where hurricanes develop?

    [Response: There are two excellent opportunities for exploring the physical processes discussed in the post more quantitatively. For looking at what THC might do to climate, and the changes in net VERTICAL heat flux in the ocean during THC fluctuations, you could look at the Rooth two-box model discussed in Marotzke’s paper, or perhaps the related box models in Gnanadesikan’s Science paper. For looking at what happens when you reduce evaporation while leaving the GHG concentration of the atmosphere fixed, the best thing is to build a simple one-column radiative-convective model with a surface energy budget. If you do that with grey gas and with an isothermal stratosphere, the equations can even be solved analytically. It’s especially simple to see what’s going on if you work in the optically thin limit. For those who know how to do such calculations, the most illuminating thing is to sit down and do it yourself. The whole thrust of the Climate Book I’m writing is to help people learn how to formulate such simple models when they need them to clarify basic points. –raypierre]

  19. 69
    Jim Clarke says:

    Dr. Gray is a pattern recognizer, as has been stated above. The physical explainations for those patterns were always secondary to his work and quite subject to change in his mind. He rests his reputation on the analysis of the patterns, not on his analysis of the physics, which he correctly and often points out, is not well understood by anyone.

    Since the 1980’s Dr. Gray has been making predictions about what was going to happen with Atlantic hurricanes and what the U.S. should do about it. His predictions have come to pass and if we took his advice, we could have saved 10’s of billions of dollars in hurricane damage by increasing building codes then, instead of now.

    In this respect, Dr. Gray has adhered to the scientific method. He observed nature, recognized what was happening and made a prediction based on that recognition. The prediction proved accurate, lending authority to his methods.

    Certainly, his explaination for what has happened is based on many assumptions and some of them have been shown to be incorrect. If this discredits him, then why does it not discredit the other side, which has also made countless assumptions which are constantly tweaked and changed as more data becomes available, and could still be totally wrong?

    The bottom line is that the AGW forecasts are not supported by the actual data (meaning the observed warming falls short of even the most minimal IPCC predictions), while Dr. Gray’s forecast appears to be right on.

    The climate community has put a lot of stock in the modelling of the most complex (unpredictable) system on Earth and asked the world to make great sacrifices based on these models. At the same time, they have discounted the proven method of pattern recognition, because it does not support their claims. Until the models show a pattern of successful predictions that is at least as good as Dr. Gray’s, there will be many who are skeptical of an AGW crises; as there should be!

    Finally, since there is so much that remains unknown about global climate change, anyone who takes a stand one way or the other on the issue is an advocate, by definition. Real Climate certainly falls into that category.

    [Response: Making predictions or statements based on easily demonstrated fallacies is just not a good idea. Gray’s successes in hurricance forecasting was based on statistical modelling that didn’t require a physical understanding to work – this is useful stuff and will work regardless of what the underlying physics actually is. The issue of anthropogenic climate change is not like that. The science of this subject is fundamentally tied to the underlying physics and no amount of correlations and statistical modelling will be able to extrapolate what will happen in the future (since we are moving into a very clear ‘no analog’ situation). If we advocate anything, it is that scientific statements should be based on what is already understood by the community – it is not a statement of certainty or of infallability. – gavin]

  20. 70
    Coby says:


    The bottom line is that the AGW forecasts are not supported by the actual data (meaning the observed warming falls short of even the most minimal IPCC predictions)

    Can you elaborate please? What was predicted, what has happened?

  21. 71
    pat neuman says:

    re 69.

    Jim, being a pattern recognizer do you think Dr Gray could tell us what pattern caused our 1930s dust bowl and why that pattern hasn’t been repeated yet?

  22. 72
    Hank Roberts says:

    I can, I think. Difference is irrigation. This time, we’re tapping the Oglalla Aquifer to make up for the current drought, and it’s not quite tapped out yet.

  23. 73
    David B. Benson says:

    Re #71, #72: Maybe irrigation? My understanding is that eventually border trees were planted to control the blowing dust. When farmers started cutting these down about 30 years ago, the local extension agents were strongly advised to encourage the farmers not to do that and also to replant border trees. It would seem that this has, so far, been successful.

  24. 74
    pat neuman says:

    re 73. 72.

    Irrigation can’t be the reason for the low humidity and absence of significant precipitation during the dust bowl years.

    For ex, summer dewpoints at Minneapolis:
    … the minima beginning in 1924 and lasting until 1937. This stretch of lower dew points matches well with the dust bowl era when precipitation was also at a minimum.
    … What does stand out beginning in the 1990â??s is the lack of dry dew point years.

    William M. Gray wrote … I judge our present global ocean circulation to be similar to that of the period of the early 1940s when the globe had shown great warming since 1910, and there was concern as to whether this 1910-1940 global warming would continue. … A weak global cooling began from the mid-1940s to the mid-1970s. The author projects this to be what we should expect to see in the next few decades.

    If Gray expects to see a return to a weak cooling period like the mid-1940s to the mid-1970s, how does he explain not seeing a repeat of 1924-1937 low dewpoints? Instead, we had a string of moist humidity years in the 1990s, which may be due to the positive water vapor feedback with global warming.

  25. 75
    Hank Roberts says:

    I gathered from prior discussion, especially here:
    that conditions are known to be quite different from those of the 1950s, but that comment basically only said that more discussion will have to happen in another forum or in publications. Dr. Chelliah did say clearly that the broad general assertions that others are making with reference to his work are not correct.

    It seems to me Dr. Gray’s claiming a similarity to the 1950s that doesn’t fit the published work Dr. Chellaih coauthored. Am I misreading the details here, anyone able to clarify?

  26. 76
    pat neuman says:

    Continuing on the dust bowl topic which Gray seems to have discounted, I added a few hydrology plots to my yahoo photos website to show how severe and widespread the early-mid 1930s drought was.

    I included plots showing Mississippi River streamflow (1874-2004), Lake Michigan-Huron (1918-2005) and Devils Lake ND (1830-2006).

    Contributing drainage area for the Mississippi River is 85,600 square miles at Clinton, IA and 1,140,500 square miles at Vicksburg, MS.

    I think the Clinton, IA plot is especially interesting, showing that conditions preceding 1940s/1970s cooling was a drying trend, while condition preceding the current is a wetting trend.

    That’s the opposite direction, and I figure to be counter to what Dr. Gray the pattern recognizer would expect if cooling would return. No going to happen the way he thinks, by the patterns I see.

  27. 77
    StormTrack says:

    Global Warming and Hurricanes: Response to Bill Gray
    From Gray and Muddy Thinking about Global Warming Anybody who has followed press reporting on global warming, and particularly on its effects on hurricanes, has surely encountered various contrarian pronouncements by William Gray, of C…

  28. 78

    #76, Pat, correct argument, not only that, Dr Gray seems not to see patterns from other influences, like from the North Pacific, the great region which contributed multiple sst enhanced cyclones which contributed to the great warming which spanned Continent wide this winter past. The trouble with focusing strictly on one cycle, or oscillation is that everything is interconnected, one regions significant weather change ultimately affects many others, but the question is really which is changing which? Or rather whether the change is part and parcel driven by Global Warming. The common thread seems to be GW, everywhere you look that is the real “pattern”, or undercurrent driving climates off kilter.

  29. 79
    pat neuman says:

    re 78. 70. Wayne, I see the global warming pattern showing up everywhere too, keeping in mind Polar Amplification (1st thread of 2006 at RC). In looking at temperature trends at NOAA Cooperative Climate stations in the U.S. the warming trends are greatest in mid-high latitudes, overnight minimums and during the winter months, which is what climate modelers have been saying would happen with global warming. In the lower latitudes, temperatures aren’t supposed to trend upward much initially, although I note in my photo plots that some climate stations in Florida and Kentucky had daily minimum temperatures in July and August of 2005 which averaged higher for that two month period than the previous 100 years of record for July-August average daily low temperatures. I suspect that may be related to higher dewpoints with global warming, not allowing the temperatures to drop as much overnight. Little or no relief during hot and humid spells.

  30. 80
    pjw says:

    Gray’s New Climate Science, Jigsaws and the Theory of Epicycles

    Gray’s thesis as expressed in his extended abstract and presentation at the AMS conference on Hurricanes and Tropical Meteorology conference were based on the stipulation that global warming observed during the three decades is part of a natural cycle, a succession of warming and cooling periods that has occurred before and will occur again. The principal driver of this oscillation is a modulation of the ocean thermohaline circulation (THC). In his congressional testimony Gray noted that an acceleration of the THC was responsible for the warming of the North Atlantic Ocean since 1995 and the subsequent increase in hurricane intensity and frequency. In the AMS abstract Gray relates the changes in hurricane characteristics to a slowing down of the THC although in some parts of the text a strengthening is still referred to as the responsible agent. Another basic assumption made by Gray is that there is a water vapor feedback does not occur following rather strictly Lindzen’s IRIS theory that has tended to fail close scrutiny. All subsequent arguments are manipulated to support these cornerstones of Gray’s hypothesis that there is no anthropogenically induced climate changes on the planet.
    The style of Gray’s presentation was familiar, oscillating between ridiculing everybody else’s scientific contribution and offering instead confident if not confused alternative perspectives. Global warming is dismissed because he states that scientists who find evidence for global warming were the same scientists in the 1970’s who thought that the planet was heading towards an ice age. Gray’s points were accompanied the now familiar diatribe against modelers. The climate system is far too complicated to model or even understand so that following the climate-modeling route was inherently flawed. However, it seems that the climate system is not too hard for Gray himself to understand and deconvolute as he proceeded to offer simple descriptions of how the climate system really works.
    Gray’s scientific exposition began with Broecker’s THC diagram. As best as I could follow, he argues that modulations of the subtropical high-pressure zones cause anomalies in the THC through enhanced or reduced upwelling throughout the depth of the ocean column in the Atlantic equatorial zones that simultaneously causes changes along the entire global route of Broecker’s circulation. These modulations of the THC change the surface heat flux by the same amount as might be produced by the water vapor feedback if it were included! It was also inferred that oceanographers simply did not understand the physics of the ocean and that as the THC was not modeled correctly it was the “Achilles heel” of those who propose global warming. Gray noted that oceanic observations of the THC were not necessary and that anomalies in the subtropical high-pressure belt were all that is needed to measure changes in the THC. I guess we could have saved a lot of money if WOCE had had Gray’s insight 20 years ago.
    Gray proposed a “new” thermodynamics. Climate scientists are “hamstrung” by an adherence to the Clausius-Claperyon relationship, which requires that saturated vapor pressure increase exponentially with temperature. Gray proposes that the reverse is true with saturated vapor pressure decreasing with increasing temperature so that there is less evaporation from a warmer ocean. But here emerges a problem. For his chain of arguments to work he must have evaporation being reduced as wind speeds increase. He ignores that part of the turbulent flux relationship involving wind speed and instead uses his new reverse C-C relationship. Gray is either unaware or ignores well-founded observational evidence that an increase in evaporative flux over the oceans has occurred during the last decades accompanying stronger winds!
    In summary, Gray proposes a theory of how he believes the climate system really works, one which goes against simple thermodynamical theory that has been around for centuries, theoretical calculations, results from climate models and diagnostic studies, all of which propose a consistent and coherent argument for climate change occurring from radiative changes associated with increasing greenhouse gases. Perhaps an analogous approach would be putting together a jigsaw puzzle, ignoring the picture on the box and using a hammer to force the pieces together irrespective of what the final picture finally produced.
    Following Gray’s talk, a number of questions were asked. I asked why he had changed the sign of the THC from speeding up to slowing down between the congressional testimony and his extended abstract to explain the same phenomenon? I also asked him if he was influenced by the Bryden et al article (Nature December 2005) and that was the reason he changed the sign? He stated that he had “..been through all of that many times..” and that these bits and pieces of data collected by oceanographers meant nothing. Ditto to the global increases in ocean heat content catalogued by Levitus in his recent series of articles. A second question from Greg Holland took umbrage at Gray’s depiction of modelers as doing something sly by promoting false or ill-conceived results. Holland noted that the problems of climate were important and that modelers were doing honorable work on socially relevant problems and that models provided the most powerful diagnostic and predictive tools available. Holland’s comment brought a large ovation from the audience.
    I have been keeping track of the data sets and published scientific findings that must be in error for Gray to be correct on the relationship between hurricane intensity and global warming and for everyone else to be wrong. These data include:
    – Ocean reanalysis data that shows global trends in ocean heat content (Levitus 2005 JRL, Barnett et al. 2005 Science).
    – Oceanographic section data such as collected by Bryden et al. 2005 (Nature December) indicating a slowing of the meridional overturning in the North Atlantic Ocean during the last decade.
    – Atmospheric reanalysis data that does not contain trends in vertical shear with SST increases during the last 35 years (Hoyos et al. 2006, Science April).
    – SMMI satellite data that has shown an increase in evaporation associated with increasing winds during the last few decades (e.g., Liu and Curry GRL, Mar 7, 2006).
    – Global tropical storm data (see for the satellite era (1970-2004). Valid questions have been raised on the quality of these data, however, in order for the trends noted by Webster et al. 2005 (Science, September 13) not to be significant around 150 storms would have to be incorrectly classified from 1970-1985 by either being missing from the data set or judged to be major hurricanes (category 3+4+5) when they were a lower category.
    – Surface flux data collected from the many tropical experiments (TOGA COARE, JASMINE) or the Pacific TAO array that show increases between surface latent heat flux with wind speed or warmer SST.
    – All climate system models which show any increase in global temperature associated with GH forcing.
    Overall, I am reminded of the Astronomical Epicycle Theory. The problem for early astronomers was how to keep Earth at the center of the universe and still explain the orbits of the moon, planets, stars and other celestial bodies. This was explained by inventing “epicycles” which were sets of ad hoc circular loops devised to explain why the celestial bodies made an apparent “loopback” motion when viewed from Earth. As astronomical observations continued to amass, the necessary epicycles became more and more complicated to fit a geocentric perspective. Copernicus and Kepler eventually clarified and simplified the system but not without social ramifications. Gray’s new climate science with its inventions and reinventions, is perhaps the modern day epicycle theory; one where inconvenient concepts or observations are warped to fit a higher “truth”.
    As the list of inconvenient data list gets longer, expect the theories of the new climate science to be modified. After all, the universe does rotate around Earth and there must be a way of explaining it. Have no doubt, epicycle climate theory is very malleable and ductile.

  31. 81
    Dano says:

    RE 80 (pjw);

    Plz do a proper citation or link to the piece you quote without attribution so informed readers can place in context.

    Thank you in advance.



  32. 82
    Steve Bloom says:

    Re #81: Dano, “pjw” is Peter Webster and this was his (very kind to us as this sort of information isn’t normally available in “real time”) report from the hurricane conference on the material relevant to this post. It’s not a quote of someone else’s work. Thank you, Peter.

  33. 83
    Ike Solem says:

    Interesting quote from #80:

    “Gray noted that oceanic observations of the THC were not necessary and that anomalies in the subtropical high-pressure belt were all that is needed to measure changes in the THC. I guess we could have saved a lot of money if WOCE had had Gray’s insight 20 years ago.”

    Climate science inherently suffers from a lack of experimental opportunities (controls) so observational data collection is very critical (otherwise, what would you be comparing the model results to?). Ocean sciences rely on pretty sparse data as it is – especially in terms of depth profiles of currents and temperature. It really seems that any scientist interested in this issue would want the most accurate and comprehensive data available, and wouldn’t want to rely on more tenuous secondary associations that are influenced by many other factors. Paleoclimate studies have to rely on secondary proxies, but not by choice! This doesn’t seem like an honest argument on the part of Dr. Gray.

    Is it even clear what fraction of northern heat transport in the Atlantic is due to the THC, and which is due to wind-driven surface ocean currents, and which is due to atmospheric transport? Tim Osborn, the UK Climate Research Unit, has a nice introduction to this at Thermohaline circulation for the uninitiated. How can anyone say that oceanic observations are not necessary in studying this very complex system?

    The epicycle analogy in #80 seems accurate. The epicycle argument was supported by interests whose main goal was maintaining the notion of infallible papal authority. The ‘natural climate change theories’ are supported by entrenched economic systems that have the very short-sighted goal of preventing the adoption of government regulations that would severely limit the use of fossil fuels; the ‘scientific viewpoints’ they promote tend to be internally inconsistent and to conflict with observations; thus they largely are funnelled out to the press through industry-funded think tanks rather then through any normal peer-reviewed process. RealClimate in some sense provides ‘independent peer review’ for this brand of ‘science’ which is one reason why RC is a valuable site, regardless of what the above detractors/distracters say.

    It is worth noting that some of Gallileo’s contemporaries refused to look through his telescope for fear of sullying their minds with artificially manipulated images. Even today, those epicycle theories persist in astrological circles (that’s what ‘Mercury in retrograde’ is referring to!).

  34. 84
    Dano says:

    RE 82:

    Thank you Steve. Obviously I missed something somewhere.

    Thank you Peter,



  35. 85
    Bryn Hughes says:

    THC slow down.
    I surmise that when ice separates from the sea the salt concentration increases.The sea becomes denser and sinks being replaced by sea with normal salt concentration.
    If the salt concentration of the sea is reduced by dilution with fresh water then it will freeze at a higher temperature but the denser sea water will still sink.
    If the THC slows down then less heat will be transported to the Arctic.
    Both these conjectures indicate that Arctic sea ice should expand.

    [Response: Just speaking for myself, I wouldn’t say that the Bryden et al paper is the last word on what the THC is doing right now. It’s probably the best attempt to date, but it’s a hard thing to do. But, what you are saying is correct, or would be correct if THC were the only thing affecting Arctic climate. In all simulations incorporating sea ice, the sea ice advances when the THC shuts down, and indeed the advance of sea ice is believed to be the main amplifier leading to such a large Greenland cooling. However, what we have now is the combined effect of anthropogenic greenhouse warming, plus the effect of whatever THC is doing. If Bryden is right and the THC is slowing down, then the THC slowdown is helping to offset Atlantic warming, and is thus preventing the sea ice retreat from being even larger than it is. Something similar does happen in some of the IPCC models which have a lot of THC slowdown in response to greenhouse gas increases — the THC slowdown doesn’t trigger a European ice age, but somewhat limits the N. Atlantic warming (at the expense of making some other part of the globe get even warmer). –raypierre]

  36. 86
    Mauri Pelto says:

    An interesting article was in EOS last week that looks at THC in a previous warm period. “Eocene Hyperthermal event offers insight into Greenhouse Warming” By Bowen et al. A key paragraph is…

    “One potential consequence of future global warming is a perturbation to the ocean’s thermohaline circulation, which may further change global climate. Indications that ocean circulation changes occurred during the PETM are thus of great significance. Surface ocean warming was amplified at high latitudes (as much as 9°C) relative to low latitudes (5°C), while deep-water temperatures rose by 4º-5°C globally [see Zachos et al., 2005, and references therein]. During the PETM, reduced pole-to-equator sea surface temperature gradients or changes in continental freshwater runoff may have shifted the site of deep-water formation from a Southern Ocean locus to subtropical latitudes or to high latitudes in the Northern Hemisphere [e.g., Kennett and Stott, 1991; Bice and Marotzke, 2002; Nunes and Norris, 2006], introducing warm water to the deep sea and driving methane clathrate destabilization and further greenhouse warming [Bice and Marotzke, 2002].”

    The point is the THC changed due to a significant warming, but it did not suppress high latitude warming at all. They point out that surface warming was amplified at high latitudes and deep temperatures rose to a lesser but still substantial amount. This does not agree with #85. THC is density driven, and if the air is warmer and the seawater is warmer it is true it will be tougher do drive deep water formation via cooling and salinity enhancement. However, this does not then lead to more sea ice production since other factors are driving up polar ocean temperatures.

    [Response: Very good remark. The combined effect of a THC slowdown plus accentuated greenhouse warming is very different from what you get from a THC slowdown alone, and may even be quite different from the sum of the two effects independently — since sea ice formation and bottom water formation locations are highly nonlinear processes. –raypierre]

  37. 87
    Grant says:

    In defense of epicycles…

    Yes, it’s a mistaken theory. But given the observational tools available to the ancients, it’s a reasonable one: it worked better than the available alternatives. When viewed as a physical construct (spheres upon spheres upon spheres) it’s nonsense, but when viewed as simply a mathematical method for calculating planetary positions, it’s quite natural — rather like a “Fourier decomposition” of planetary motions.

    Copernicus retained them in his model of the solar system, but showed that by assuming a heliocentric rather than geocentric system, far fewer epicycles were required, simplifying calculations considerably.

    It wasn’t until Kepler than a viable alternative was offered: elliptical orbits. This was not a leap of faith, but of mathematics. To my knowledge there was no ecclesiastical objection to Kepler’s idea — abandon epicycles in favor of ellipses. The objection was to the heliocentric idea.

    And I think that objection wasn’t fueled by devotion to papal infallibility, but by scriptural fundamentalism.

    [Response: I’ll grab the last word on the question of the Catholic Church vs. Gallileo (hopefully a conciliatory one), but then ask that we not get any further into the admittedly interesting questions of Vatican science policy at the time of Gallileo. I merely want to emphasize that Gallileo’s problems with the church do not reflect any deep-seated conflict between science and religion, the more so since the Vatican has never embraced scriptural fundamentalism. In some sense, the Vatican’s earlier stance (informed much by Aquinas) in some ways was an attempt to state that there was no essential science/religion conflict. The problem was that the “resolution” was based on an Aristotelian and perhaps heliocentric geocentric view of the Universe, and papal authority was behind that. In my view, the problem came from an injudicious use of papal authority. The notion of infallible authority is indeed inimical to science, which has to be mutable and evolve in response to new data and new theories. I like to think that the Vatican has become somewhat more judicious since, in what it puts papal authority behind. It will always be hazardous to put papal authority behind the kinds of questions that are quintessentially answered by science, as opposed to those areas where theology has the most to say. Sorry for intruding these thoughts, but since we let some of the preceding discussion through I at least wanted to end on a note that avoided the implication that there was some unbridgeable gap. here. –raypierre]

  38. 88

    I attended two seminars in DC yesterday – one given by Dr. Kerry Emanuel, the other by Dr. Chris Landsea, both about recent changes in tropical cyclone frequency and intensity and how they may be related to (anthropogenic) global warming.

    While there were many similarities between the presentations, there were two major points of disagreement: 1) are major hurricanes the current era (last decade or so) really stronger or more frequent than they were in the past, and 2) is the AMO a naturally occurring phenomenon.

    On the first point, Dr. Landsea suggests that changes (improvements) in observing practices over the years (including post-1970) quite possibly have led to the more frequent identification of major hurricanes and that this effect has not been adequately accounted for by the studies of Emanuel and Webster et al. Dr. Emanuel countered that he used windspeed corrections based upon Landsea’s (earlier) published recommendations (which Landsea now contends are unwise), and Dr. Webster notes (in his comment #80 above) that 150 major storms would have had to be missed or misclassified (globally) in order for his results to be much effected. Dr. Landsea gave evidence that total number of missed or misclassified storms could be significant.

    On the second point, Dr. Emanuel showed that there is a strong correlation between the 10-yr smoothed record of Northern Hemisphere temperatures and the 10-yr smoothed record of SSTs in the main development region (MDR) for tropical cyclones in the North Atlantic. He pointed to this strong correlation as evidence that the MDR temperatures are simply following the larger-scale temperature of the Northern Hemisphere (and globe for that matter) as they have responded to a combination of natural and anthropogenic forcings (GHGs and solar in the early part of the 20th century; GHGs and sulfates in the mid-part of the 20th century; and primarily GHGs since then). Dr. Landsea suggests that perhaps the circulation changes in the North Atlantic are a significant contributor to the NH temperature changes. Dr. Kerry contends that this is the tail wagging the dog, and this so-called Atlantic Multidecadal Oscialltion (AMO) is simply a statistical artifact of the large-scale temperature changes brought about primarily by anthropogenic forcings. In fact, Dr. Emanuel went as far as to say that even Mike Mann, who gave the moniker of AMO to the phenomenon, now dismisses the idea that it is a natural oscillation, and in fact, he too, believes that is only a manifestation of larger-scale temperature trends.

    However, Dr. Emanuel made no mention of the recent paper by Knight et al. that documented an AMO-like oscillation in unforced climate model runs. The authors concluded:

    Our 1400 year model simulation exhibits multidecadal climate variability with a similar pattern and amplitude to that of the AMO in observations. Together with the similarity of the simulated 70-120 year period to the observed 65 year period, and the range of periods derived from palaeodata (40-130 years) [Delworth and Mann, 2000; Gray et al., 2004], this suggests the model simulates a realistic AMO. Its presence over many centuries in the model supports the suggestion from observations and proxy data that the AMO is a genuine repeating mode of globalscale internal climate variability.

    This suggests that an AMO-like oscillation does exist (at least in some models) without anthropogenic influences.

    Honestly, I am not trying to be difficult here. Scientists have the right to change their minds (in fact they should) when faced with data and observations that run counter to their earlier understanding. Dr. Landsea apparently has done this when it comes to the appropriateness of wind speed adjustments in the early tropical cyclone record, and Dr. Mann (at least according to Dr. Emanuel) has done this when it comes to the phenomenon of the AMO. If Dr. Emanuel is correct in his characterizations of Dr. Mann’s thinking about the AMO, I think that it would do a great service to the entire community for someone at RealClimate, perhaps even Dr. Mann, to take us through the current best thinking about the origins of the AMO signal in the temperature record of the Atlantic Ocean – both the 100 or so year observed record as well as the 1400 year simulated/reconstructed record.

    It is all rather confusing that the peer-reviewed record indicates one thing, and yet the current thinking by a number of prominent scientists is for another. As I am a (somewhat) active researcher/commentator in the field of climate/hurricane relations, I find myself in a bit of a quandary… when I cite the published literature I am told that I am wrong, but I have nothing else to go on, I don’t think RC discussion are citable, are they?

    Thanks for considering an explanation.

    -Chip Knappenberger
    (primarily funded by the fossil fuel industry since 1992)
    (benefiting from fossil fuels since 1964)

    PS. As an interesting aside, Dr. Emanuel said that he is working on a theory (he did not go into details about it) that holds that intensification of North Atlantic tropical cyclones from global warming will lead to an acceleration of the THC!

    [Response: The ‘new theory’ isn’t so new, Emanuel has published before on the potential link between tropical mixing in the ocean (in which hurricanes may play a significant role) and it’s effect on the overturning. The basic idea is that the THC is a balance between polar deep water production and mixing. In models at least, the strength of the THC is positively dependent on the net amount of mixing. The link to hurricanes is intriguing, but not yet widely accepted. However, it would follow then that if hurricanes increased that that would eventually lead to an increase in THC. Pretty speculative though… – gavin]

    [Response: Kerry’s Hurricane-THC link takes off from the results of the famous “Abyssal Recipes” papers by Wunsch and others, which noted that one needs to input mixing energy into the ocean in order to bring up deeper water against stable stratification and sustain a deep ocean circulation. More hurricanes could increase the vertical mixing in the tropics, allowing more cold water to upwell in the Tropics (where it only rarely does now); one of the more intriguing possibilities is that the resulting tropical mixing could help explain the low-gradient Eocene climates, by cooling the tropics while stimulating ocean circulations that transport more heat poleward. There are a lot of open questions in terms of how this would work, and given that the hurricane induced mixing wouldn’t tap into the really deep water, I’m not sure I’d describe the effect as enhancing “the” THC, as opposed to stimulating a new kind of oceanic heat-transporting circulation. No question, though, it’s an interesting development and is all part of the process of figuring out what a high CO2 greenhouse world would be like. –raypierre]

    [Response:Chip, some comments on your statement: “Mann, who gave the moniker of AMO to the phenomenon, now dismisses the idea that it is a natural oscillation, and in fact, he too, believes that is only a manifestation of larger-scale temperature trends.” The first part is correct. I did coin the “AMO” in an interview with Richard Kerr some years ago for a news article he was doing on Delworth and Mann (2000). The term first appeared in Kerr’s article. The 2nd part of your statement is not correct. I have not dismissed the idea that there is a natural multidecadal climate oscillation involving coupled ocean-atmosphere processes in the North Atlantic. Indeed, I’ve published a number of papers providing support for this assertion (Mann and Park, 1994;1996; 1999;Delworth et al, 2000; Knight et al, 2005). However, in almost all of these analyses, the signal is found to have very little if any amplitude at all in the tropical Atlantic (see figures 21 and 31 in the Mann and Park, 1999 (warning, 5MB!) review paper [Mann, M.E., Park, J, Oscillatory Spatiotemporal Signal Detection in Climate Studies: A Multiple-Taper Spectral Domain Approach , Advances in Geophysics, 41, 1-131, 1999.]). I don’t know if you’ve accurately quoted Kerry or not, but presumably he was referring to the fact that my own analyses have shown little evidence that the AMO is associated with any detectable oscillatory pattern in the tropical Atlantic SSTs relevant to Atlantic Tropical Cyclone development. –mike]

  39. 89
    Steve Bloom says:

    Gray associate Phil Klotzbach has posted an in-press GRL paper here (thanks to Roger Pielke Jr. for the link). It seems to be a frontal attack on Emanuel and Webster et al. The lack of any co-authors is interesting, especially as I don’t think Klotzbach has a PhD.

  40. 90
    Roger Pielke Jr. says:

    Re: 89. Klotzbach is a Gray PhD student, who apparently has now taken over primary responsibility for the Gray et al. seasonal hurricane forecasts. The paper we linked to is peer-reviewed, and rather than being an “attack” on anyone, in my view it should properly be viewed as an effort to advance the evolving science of tropical cyclones and climate. Klotzbach raises some interesting questions for the scientists to discuss, and from the standpoint of my research, he provides extremely valuable information related to disaggregating the factors underlying the global growth in disaster losses.

    Klotzbach has also posted some “talking points” on the paper here:

    And we’ve opened up a discussion (surprisingly silent so far!) on this paper here:

    We welcome discussion. Thanks.

  41. 91
    pjw says:

    Re: 87

    Grant, you are quite right. The old astronomers didn’t have the tools. But Gray does have: data, model results and theory but refuses to use them or believe in them. Rather, he conjures up new relationships to fit the result he wants. Why? I think he really believes that all climate change is natural and therefore all contrary evidence. It seems to me to be more of a religious belief than a scientific one.

  42. 92
    raypierre says:

    Regarding the various points raised on the mechanism accounting for the Dust Bowl —

    I’m glad this topic came up, since it gives me the chance to emphasize that the criticism of Gray’s claims about the influence of THC fluctuations on climate should not be taken to mean that fluctuations in ocean dynamics have no significant effect on climate. To the contrary, natural fluctuations on decadal and longer time scales can have a big influence, especially on precipitation patterns, and the the way ocean dynamics responds to GHG forcing is almost certainly a big player in determining what regional climate change patterns will look like. For the specific subject of the Dust Bowl, I point people to the excellent summary of research on the influence of SST on N. American precip, by Richard Seager at . This work indicates that the Pacific ocean temperature patterns play the biggest role in the Dust Bowl and similar droughts. It doesn’t take on the question of what kinds of changes in the ocean current patterns might have led to these SST changes, though.

  43. 93
    David B. Benson says:

    Chip Knappenberger — As I understand it, RealClimate posts, together with the comments, are ‘archival’ in that the intent is to perserve all the text ‘forever’. So in a wide variety of academic disciplines, citing this material would be perfectly accetable. All that is required is enough linkage information that anyone reading your work could, if they wished, go check the original post or comment themselves.

    There are several minor variations in approved citation style. Looking at almost any entry in the on-line Encyclopeda Britannia will illustrate a few of the acceptable styles.

    [Response: I think citation of material on web sites is a somewhat gray area, at least in academic journals. Digital archives maintained by organizations like AGU or AMS have a clear status, because the digital version of the journal article is now the version “of record,” and these hopefully long-lived organizations have committed to maintaining a digital archive in perpetuity. That still makes a lot of people nervous, since if a publisher goes bust, the print versions of journals don’t disappear from libraries, which is not the case for digital archives. Sites like RealClimate are more problematic, since we have no way to guarantee how long our material will remain available — though we do intend to stick around, and have the intention of keeping our articles available in the original form in which they are posted. Still, citing RealClimate will never be the same as citing the New York Times or the AGU journals. What complicates things even more is that many of the links provided on RealClimate and other sites are to material that may itself be transitory. –raypierre]

  44. 94
    Hank Roberts says:

    The “Digital Archive” — — (a.k.a the “Wayback Machine”) can be used to find/cite and retrieve material that’s disappeared from the official resources on the Web.
    An example, last I wanted to reread the famous 1994 paper “Ozone and Global Warming: Are The Problems Real” by Sallie Baliunas, which used to be available online from the George C. Marshall Institute, in which she said among much else,:

    “ozone recovers every year after a month or so. The dramatic Antarctic ozone decline is a temporary annual event…. the “hole” cannot gobble up the rest of the world’s ozone; the hole is confined to the frigid isolation of the Antarctic stratosphere’s polar vortex…. the ozone hole cannot occur in the Arctic.”

    She went on to argue that global warming was as flawed as the “ozone hole” notion:

    “… compare the forecasts to very accurate temperatures measured by satellites …. The Arctic is important because the forecasts say that Arctic temperatures rise fastest of all and thus provide a stringent test of the greenhouse warming theory…. the satellite readings show that the
    temperature has not changed at all in the last 15 years in response to the buildup of greenhouse gases … warming in the next century, at present rates of increase in the greenhouse gases, will be less than 0.5 [degrees] C. Spread over a century, that warming will be insignificant and indistinguishable from the natural fluctuations in the earth’s temperature. … Why are the predictions so far off?”

    Material like this shouldn’t be lost, it’s priceless for perspective on how the science was used to make the public policy decisions in the late 1990s.

    Only the web archive had a copy when I looked for it; found here:*/

  45. 95
    pat neuman says:

    In his paper,

    Gray wrote … A weak global cooling began from the mid-1940s to the mid-1970s. The author projects this to be what we should expect to see in the next few decades. …

    Gray concludes with … I anticipate global temperature conditions will change as they have in the past. I expect to live to see the start of a global cooling pattern and the discrediting of most of the anthropogenic warming arguments. The world has more serious problems to worry about.

    Does Phil Klotzbach agree with Gray on that?


    [Response: I think what matters is what Klotzbach wrote in his GRL article. In this matter, the devil is in the details of how the data analysis is done, and I look forward to seeing how the ensuing dialog between Klotzbach, Webster and Emanuel shakes out. –raypierre]

  46. 96
    Gerald Machnee says:

    From #12: “The El Nino example is quite pertinent to the THC related issues discussed in the article. El Nino can affect the global mean temperature through its influence on the surface budget, so why not the THC? In fact, the THC can influence the global mean temperature — either through nonlinearity like sea ice or clouds which can give you an effect on the mean even in steady state, or through transient effects which allow you to tap more deep cold water (for a while) and bring it to the surface. It’s not that the THC can’t affect global mean temperature — it does, in Vellinga and Wood’s experiment–”
    Many comments are being made about Gray and THC, but nobody has replied to the question raised in this post as to why only El Nino may affect global temperatures.

    [Response: Who said only El Nino can affect global temperatures? As I said, in the very statement you quoted, the THC does affect the global mean temperature — just not in a way that duplicates the anthropogenic global warming signal. For the case of a weakening THC, the sign isn’t even right. –raypierre]

  47. 97
    pat neuman says:

    Re: 95.

    I still would like an answer … Does Phil Klotzbach agree with Gray on that?

    I would also like to know if there is anyone out there who agrees with the last two sentences that William Gray made in his paper (95.).

  48. 98
    Bryn Hughes says:

    Raypierre, Re your comment to 85
    Therefore there will be a ngative feedback: expanding sea ice will mitigate global warming.
    Why is Antarctic sea ice expanding?

  49. 99
    Urs Neu says:

    Re 88

    Concerning the AMO-like oscillation in unforced climate model runs (Knight et al.):

    I have some concerns about the relation of the simulated patterns with the AMO:

    – the range of periods (40-130 years) in the paleodata is so huge that it is questionnable if this is anything else than a random (possibly forced) signal. It is hard to find any regular signal in the AMO proxy reconstruction by Gray et al. (2004). As also pointed out by Emanuel, the global temperature signal shows periodicities in the 50-70 year band due to the accidental superposition of non-periodic external forcing, at least during the last 150 years. Of course it is possible that there is an additional natural cycle at the same time, but it would have to be more or less exactly in the same phase as the overlaying forcings, which is possible but not very likely. Delworth and Mann (2000) analysed global temperature for their frequency analyses of instrumental data.

    – the oscillation due to THC variations in the models used in Delworth and Mann (2000) and in Knight et al. (2005) are in a different frequency range and thus depend on the model: 50-80 years vs. 70-120 years, respectively. The match until now only concerns the frequency band, nothing is said about matching of the phase. There isn’t any observational evidence that such a THC oscillation as seen in the models exists in the real world.

    Conclusion: given the mentioned frequency ranges the only thing one can say is that both, modeled THC and temperature observations, show multidecadal variation. However, this is a very weak basis for arguing that there is a causal relationship. On the other hand, the oscillating temperature signal can be well explained with external forcings.

    [Response: Urs, thanks for your comments on this. Your points are well taken, but I don’t agree with several statements you’ve made. While I can’t speak for Gray et al (note: this is a different Gray!), other analyses of proxy reconstructions have specifically rejected the null hypothesis of red or coloured noise. i.e., there is multidecadal long-term variability that cannot be dismissed as noise–there is indeed evidence that it is bandlimited in the 50-70 year timescale range. Detecting such a signal in the short observational record is very difficult indeed, and is typically attempted through an analysis of the spatiotemporal variance in the record, which can allow the detangling of competing low-frequency signals–be they externally forced or internally generated–by exploiting spatial orthogonality (though not without some strong caveats). Please refer to the detailed literature provided in response to Chip K.’s previous comment above. The reason for believing that there may be a natural multidecadal oscillatory signal in the observations is based on the similarity in both the timescale and the spatial pattern of the signal (see again the model/data comparisons described by Delworth and Mann). All this having been said, where we may concur is that much of the 20th century variability that has been attributed recently to the “AMO” (e.g. tropical Atlantic warming and Tropical Cyclone activity) would more plausibly appear to be a manifestation of the response to competing anthropogenic forcings (i.e. 19th-20th century greenhouse forcing with a substantial offsetting tropospheric aerosol forcing in the Northern Hemisphere which really kicks in during latter half of the 20th century). – mike]

  50. 100
    Hank Roberts says:

    >85, 98
    Bryn, first you “surmise … conjectures” that sea ice will increase.

    Ray replied that “what you are saying … would be correct if THC were the only thing affecting Arctic climate.”

    THC change and climate change from global warming are, this time, both happening together — your surmise conjecture is not correct.

    Then you ask “why is Antarctic sea ice expanding?”

    Question — who says Antarctic sea ice is expanding? Over what period? And what is your source/cite/reference? Where did you read this, who are you relying on for your facts?

    [Response: Your criticisms regarding the Arctic and Bryn’s false inferences regarding a purported stabilizing effect of sea ice are on-target. However, with regard to the Antarctic, it is true that sea ice is retreating strongly only in one sector, with increases that more than compensate in other sectors. At least, that’s been the pattern over the last decade or so (see, or William’s comments at ). Antarctic sea ice has a very strong seasonal variation, and the global warming signal is not yet as dominant in the Southern Hemisphere as in the Northern, because of the thermal inertia of the massive Southern ocean. Hence, oceanic fluctuations have a better chance to dominate the pattern. Right now, I’m looking into what the AR4 models do to 2oth century Antarctic sea ice, to see whether they give a clear indication yet as to what we should be seeing in the Southern Hemisphere. Certainly, all the models predict that ultimately (by 2050) Antarctic sea ice should be dominantly in retreat. –raypierre]