Cloudy Controversies: The Science Behind the Spencer-Braswell Paper

There’s a lesson to be learned from an editor’s having resigned over his journal’s publication of a research report thought to have been inadequately reviewed: extraordinary claims must be supported by extraordinary evidence. Headline writers and media … take note.

“New NASA Data Blow Gaping Hole In Global Warming Alarmism” was the breathless headline in Forbes, referring to a paper published in a relatively new but reputable academic journal, Remote Sensing.

The paper posted in late July was written by climate scientists Roy Spencer and William Braswell. The story was subsequently picked up by the Drudge report and Fox News, warning that “new findings throw the entire global warming theory into question.”

What is interesting is that the actual paper by Spencer and Braswell, while considered by a number of sympathetic and unsympathetic critics as having some flaws, makes relatively modest claims that bear little relation to the subsequent headlines appearing on conservative-leaning media outlets. Now that the editor-in-chief of the journal that published the initial paper has resigned in protest, and a rebuttal is being published in a major climate science journal, it is worth taking a moment to move past the hype and drama to take an indepth look at the actual science being discussed.

The issue at hand involves quantifying climate sensitivity, which is commonly defined as how much warming of Earth’s surface would be expected as CO2 increases. Climate scientists (even those like Spencer and MIT’s Richard Lindzen, both outspoken “skeptics”) tend to agree that simple radiative transfer models predict about 1 degree C (1.8 degrees F) average global warming for a doubling of atmospheric carbon dioxide. The big question is how much natural processes, referred to as feedbacks, will amplify or dampen this response.

There are a number of important feedbacks (at least over a century timescale) that will affect the amount of warming we end up with, including water vapor, clouds, the lapse rate, and albedo. Of these, water vapor is almost universally considered to be a positive feedback (increasing warming), while the effects of clouds are still largely uncertain. Clouds can both trap in additional heat and reflect incoming radiation, and scientists are still fairly unsure which of these effects is larger, though most climate models predict that the positive feedback will slightly win out.

There has been a vigorous debate in the scientific literature over the past few years between Andrew Dessler at Texas A&M University and others who argue that satellite data suggests a positive feedback from clouds, and Lindzen, Spencer, and others who argue that it shows an uncertain or negative feedback. The recent article by Spencer and Braswell is in many ways a response to the criticisms of their earlier paper by Dessler in 2010.

Much of the debate revolves around the question of how much variations in temperatures over the past 10 years are a result of El Niño events and how much is “forced” by clouds. Traditionally, changes in cloud cover were considered as a feedback to external change in the system, rather than as a driver of change in-and-of themselves.

Spencer and Braswell argue that natural variability in cloud cover could make it difficult to diagnose the magnitude of feedbacks and may bias earlier studies that showed a positive cloud feedback. Specifically, they point out that there may be non-radiative forcing as a result of natural changes in cloud conditions that complicate the picture, and they conclude that “without knowledge of time-varying radiative forcing components … feedback cannot be accurately diagnosed.”


Figure from Spencer and Braswell 2011. The green line shows observations from the Hadley Centre, while the blue and red lines show the three most sensitive and least sensitive models of 13 examined.

In their recent paper, Spencer and Braswell compare the three highest and three lowest sensitivity climate models over the past 10 years to surface temperature records produced by the Hadley Centre in the UK (HadCRUt). They find that the models they examine all do a poor job of replicating the observed temperatures, and the lower sensitivity models are slightly closer to observations than higher sensitivity models, though the lack of error bars precludes determining how significant these differences actually are.

They conclude with a heavily caveated statement that “While this discrepancy is nominally in the direction of lower climate sensitivity of the real climate system, there are a variety of parameters other than feedback … which make accurate feedback diagnosis difficult.”

Their paper contains no statements that are particularly exceptionable, and certainly nothing to justify the misleading headlines that followed. The University of Alabama in Huntsville press release accompanying their paper, however, was titled “Climate models get energy balance wrong, make too hot forecasts of global warming” and contained a number of statements critical of climate models that were not contained in their paper.

From there, the story exploded, and the editor of the journal Remote Sensing resigned to “personally protest against how the authors and like-minded climate skeptics have much exaggerated the paper’s conclusions in public statements.”

Other climate scientists had similar reactions to the affair, with MIT’s Kerry Emanuel remarking that “I have seldom seen such a degree of disconnect between the substance of a paper and what has been said about it.”

Georgia Tech’s Judith Curry in a blog posting summed up her thoughts: “So should the paper by Spencer & Braswell have been published?” Yes, she replies, adding that “Ideally, it would have undergone a more rigorous peer review and have been improved as a result of that process. Spencer & Braswell make some points that are worth considering, but this needs to be done in a more rigorous manner (and with much less hype).”

As of September 11, her posting had prompted more than 300 comments, many of them technical but providing lots of grist for those wanting to drill down.

Andrew Dessler has a response to the Spencer and Braswell paper, which will shortly be published in the journal Geophysical Research Letters.

Dessler begins quite clearly by pointing out how “the usual way to think about clouds in the climate system is that they are a feedback — as the climate warms, clouds change in response and either amplify (positive cloud feedback) or ameliorate (negative cloud feedback) the initial change.”

He suggests that Spencer and Braswell’s formulation — that clouds are both a cause of and feedback on climate change — is rather outside of current norms.

Dessler points out too that Spencer and Braswell don’t actually quantify the size of variability in cloud forcings or feedbacks, but rather simply assumed it to be large relative to other climate factors. He goes through an exercise of computing these values based on satellite measurements and other datasets, and he argues that energy trapped by clouds can explain only a few percent of the surface temperature changes, much less than claimed by Spencer and Braswell.


Figure from Dessler 2011. The blue line shows the temperature record used by Spencer and Braswell (HadCRUt), while the other red lines show other major temperature records and reassessments (NASA’s GISTemp, ERA, and MERRA). The thin black lines are all 13 climate models considered, while the ones with the + symbols are those highlighted by Spencer and Braswell.

Responding to Spencer and Braswell’s comparison of high and low sensitivity models to observations, Dessler points out that Spencer and Braswell exclude a number of models that do reasonably well at matching observations, and also choose the surface temperature set (HadCRUt) with the largest deviation from models over the period in question. He creates his own chart that shows a much more nuanced picture. He also notes that the models that best agree with observations are the ones that do the best in replicating El Niño events, and suggests that “the ability to reproduce ENSO is what’s being tested [by Spencer and Braswell], not anything directly related to equilibrium climate sensitivity.”

The back-and-forth in the scientific literature will likely continue for some time on this subject, and our understanding of the processes involved will likely be better for it. In the mean time, to paraphrase the late Carl Sagan, be skeptical of any extraordinary results that are claimed in the absence of extraordinary evidence.

And yes, that reminder applies to headline writers too.

Zeke Hausfather

Zeke Hausfather, a data scientist with extensive experience with clean technology interests in Silicon Valley, is currently a Senior Researcher with Berkeley Earth. He is a regular contributor to Yale Climate Connections (E-mail: zeke@yaleclimateconnections.org, Twitter: @hausfath).
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15 Responses to Cloudy Controversies: The Science Behind the Spencer-Braswell Paper

  1. Erl Happ says:

    “Traditionally, changes in cloud cover were considered as a feedback to external change in the system, rather than as a driver of change in-and-of themselves.”

    And that is the nub of the matter.

    Historically, atmospheric specific and relative humidity and precipitable moisture actually fell away as the surface warmed.

    Every warming event is accompanied by an increase in precipitable moisture, but until very recently the increase was never enough to maintain parity. Cloud cover fell away adding to the warming tendency because more solar radiation reached the surface rather than being reflected by clouds.

    How do you read that? Positive or negative reinforcement?

    If the warming was due to increased radiative feedback how come the evaporative processes failed to keep up.

    If the evaporative processes failed to keep up was the warming due to something other than radiative feedback, for instance a warming of the cloud bearing layer due to an admixture of ozone from the stratosphere….the most potent greenhouse gas of them all?

    It can be observed that a 1°C warming at the surface of the Southern Ocean is associated with a 3°C warming at 200hPa. Which is the chicken and which the egg?

    Polar processes are closely associated with the evolution of the ozone content and temperature of both the stratosphere and the upper troposphere.

    The greenhouse model is just too simple. Reality is something entirely different.

  2. Good post. It’s worth noting that Judith Curry’s postings on this topic – she had three – have generated a staggering 2,327 comments to date! Most, as you note, are technical, but still. (You can see her postings on Spencer here: http://judithcurry.com/?s=spencer)

    But the larger question, in my mind, is how do you deal with a scientist like Roy Spencer, whose findings appear to repeatedly challenge established atmospheric and climate science and are, in turn, repeatedly found to be incorrect or not quite what he originally claimed. Does this really advance the science, or is it more of a distraction?

    Kevin Trenberth, John Abraham and Peter Gleick – three well-established scientists – addressed this point in an opinion piece we published earlier in the month. But the lesson, it seems to me, is that journalists – and journal editors! – should be aware not just of extraordinary claims, but also the claimant’s background.

    Trenberth et al’s piece can be found here: http://wwwp.dailyclimate.org/tdc-newsroom/2011/09/spencer-faulty-science

    • Barry Elledge says:

      Quite obviously, Spencer and his papers very substantially advance the discussion. From the Spencer-Dessler interaction, we necessarily conclude that none of the 13 climate models adequately reproduces the empirical temperature response to natural forcings; however, the models which come closest to matching the data are those which better reproduce the ENSO oscillations. Thus 2 or 3 of the 13 models are substantially better than the others; the other 10 or 11 should be thrown in the dustbin of climate hypotheses. This constitutes a substantial advance.

      The models which should be discarded include those which show the highest sensitivity to forcings. This implies that all the high estimates of climate sensitivity to CO2 are erroneous. At the least, the warming disaster is further away than the more extreme IPCC scenarios have suggested.

      None of the 13 models reproduces the timing or magnitude of the heat loss prior to a thermal minimum. The 2 or 3 better models adequately reproduce the timing but not the magnitude of the heat loss following a thermal maximum. Clearly the climate community needs to produce more accurate and reliable climate models before we can use them to predict the consequences of any climate forcing.

      This failure of current models indicates that we should be sceptical of assertions that CO2 increases are the primary cause of recent warming and will cause catastrophic future warming. Such claims are based exclusively on the modeling; temperature changes do not bear any distinctive signature of their cause. Both Spencer’s paper and Dessler’s response should give us reason to doubt our projections of the future climate consequences of increasing CO2.

    • chris says:

      Douglas, you wrote:

      “It’s worth noting that Judith Curry’s postings on this topic – she had three – have generated a staggering 2,327 comments to date! Most, as you note, are technical, but still.

      I had a look at those comments (not all of them!). I wonder whether (a) you meant to say “not technical”, or (b) you have a different conception of “technical” to me. Most of them seem to have been written by what we in Blighty quaintly call “nutters”. Here’s snippets from the first 10 of the 2000-odd, and it doesn’t get a whole lot better!:

      ONE: Maybe “the consensus” routinely trivializing (or worse) skeptical papers is a “backlash” against fraudulent attempts to discredit scientific research by people that are strongly associated with many “sketpics?”

      TWO: “They did it first … 2nd … 3rd … 2000th … 4000th … etc etc.”

      THREE: It is uncanny how often you mange to prove my point, Bruce.

      FOUR: The point that AGW is overhyped nonsense? Ok.

      FIVE: Yes. The climate scandal is coming apart at the seams!

      Decades of government deception are being exposed

      SIX: For society’s sake, may we now have the wisdom to:

      SEVEN: Deception in government science since Henry Kissinger met Chairman Mao secretly in 1971:

      EIGHT: It may be a mere coincidence that government scientists have promoted misinformation since 1971 about…

      NINE: It took 40 years to recognize that the SSM model of the Sun and the AGW model of Earth’s climate are two peas in the same pod..

      TEN: The “consensus” group is in the driver’s seat with their alleged 97% majority (and dominance on editorial boards)..

  3. AMac says:

    This is a useful post, for those of us on the sidelines with only a meager grasp of the substantive issues in the Spencer – Dessler cage match.

    On the politics as distinct from the science, not everybody was charmed by the three well-respected scientists’ opinion piece referenced above by Douglas Fischer. Roger Pielke Sr., for one, has been critical of the framing and rhetoric employed by Trenberth et al.

  4. Steve Brown says:

    extraordinary claims must be supported by extraordinary evidence/

    I agree and that is what is at the root of the whole climate debate. The climate sensitivity that is claimed by the IPCC modellers is a multiple of that which CO2 would cause in the absence of feedback mechanisms. That is the extraordinary claim.

    The evidence for that extraordinary claim is somewhat lacking.

    • Patrick M says:

      “The climate sensitivity that is claimed by the IPCC modellers is a multiple of that which CO2 would cause in the absence of feedback mechanisms. That is the extraordinary claim.
      The evidence for that extraordinary claim is somewhat lacking.”

      Well stated. Models should be treated as mere hypotheses until validated.

      Work, like S&B, to check whether the data actually does match the model, and to determine empirically some key parameters for GCMs, is useful and advances the science.

  5. Eli Rabett says:

    A comment by Trenberth, Fasullo and Abraham based on TF’s Real Climate comment appeared in Remote Sensing today. The take home is that climate models with a good description of El Nino/La Nina do a good job of reproducing the observations.

    • HAS says:

      No that isn’t the take home.

      The take home is Trenberth et al assert: Our results suggest instead that [S&B’s result] is merely an indicator of a model’s ability to replicate the global-scale TOA response to ENSO. from finding one model (ECHAM5) that purportedly replicated the observations well, coupled with an unreferenced and controversial in the literature claim that ECHAM5 is a good at modelling ENSO.

      It is all proof by example and assertion.

  6. Mac says:

    NB Dessler’s 2011 paper, as yet unpublished paper, has undergone correction by Spencer.

    This must be a first for climate science. A rebuttal paper, fast-tracked, peer reviewed, accepted, corrected by the scientist rebutted that has still to be published by the author.

    Amazing!

    Also we have a non-peer reviewed rebuttal by Trenberth (2011) of a peer-reviewed paper by Spencer (2011) in Remote Sensing all because the original peer-reviewed rebuttal by Dessler (2011) contained major errors.

    Amazing!

    Now due to mess created we now have a blog review of Dessler (2010) that establishes that that too contained major errors.

    Amazing!

    All that can be established in this row is that climate scientists know very little about climate or science.

    How come that doesn’t amaze?

    • chris says:

      Mac, the version of the Dessler proof on the Geophys Res Lett site is the same now as I downladed a few weeks ago. Dessler doesn’t list Spencer is his acknowledgements. So the notion that Dessler has had his paper undergone “correction” by Spencer is an odd one! I wonder Dessler may be going to clarify Spencer’s position in his Intro perhaps? We’ll see. I suspect that any changes to the proof will have negligible effect on the science.

      So that specific point certainly doesn’t “amaze”…

      Your second point seems like unsubstantiated nonsense unfortunately, and it certainly doesn’t “amaze”…

      Your last point is the only one of interest. But it would be silly to assert that everything about climate science is known. There’s a massive amount known about the role of CO as a greenhouse gas, the water vapour feedback is empirically established and so on. Obviously there are some low-level elements of uncertainty (those are the arenas that working scientists inhabit), but the fact that some models do and some don’t do quite well in reproducing a certain set of empirical observations of short term lagged TOA radiative flux responses to changes in surface temperature doesn’t have very much necessarily to say about what we “know” about climate science.

      Perhaps you’re rather too easily “amazed”!

  7. Mack says:

    All science students at Yale should read this, (it might take a couple of days :) )
    http://jennifermarohasy.com/author/nasif-s-nahle/

  8. Dr. Jay Cadbury, phd. says:

    @Zeke

    Zeke, nice to meet you. I had suspected you were probably a 25-26yr old but I would say by the grey beard you are slightly older than that. Zeke, I have several questions about global warming that I have not had adequately answered.

    Firstly, let’s begin with the 1988 James Hansen testimony. They shut off the air conditioner and opened the windows to make the room hotter. This is very disingenuous to me and it immediately makes me suspicious of the theory alltogether.

    Next, I am wondering how anyone can attribute the temperature and/or the weather to manmade co2 emissions for several reasons. One, earth is below it’s average temperature and below average atmospheric co2. How then, can you prove that the recent warming is manmade? Your essentially saying that something that happened on a much greater scale before, is happening on a smaller scale and for a different reason. This doesn’t make much sense. Also, as Dr. Giaver said recently “how can you measure the temperature of the whole earth” especially when we know the surface station siting is awful?

    When Al Gore became Vice President under Clinton, he fired Will Happer and we now know that it was because Happer disagreed with the theory of global warming.

    Regarding arctic ice melt, and I know there is a distinction between the land ice and the sea ice but I believe it is the sea ice that is melting? Why don’t any of these alarmists show the temperature of the area in question that is melting? I have a theory, my theory is that the temperature hasn’t changed much at all and the reason we see ice melting is due to natural causes. Furthermore, because satellite measurements of ice only started in 1979, nobody can really make a definitive statement about the causation, correct? Additionally, the ice caps have melted completely before, correct?

    Is it not more accurate to say that the globe is in an overall period of global cooling since earth is below it’s average temperature?

  9. Dr. Jay Cadbury, phd. says:

    @Eli Rabbet

    Fortunately that is just an opinion of the data and many scientists disagree with “the team”.

  10. chris says:

    Mac (September 16, 2011 at 10:31 am), re your:

    “NB Dessler’s 2011 paper, as yet unpublished paper, has undergone correction by Spencer.

    This must be a first for climate science. A rebuttal paper, fast-tracked, peer reviewed, accepted, corrected by the scientist rebutted that has still to be published by the author.

    Amazing!”

    As I said above (September 18, 2011 at 10:05 am), that really is silly. Dessler’s paper hasn’t been “corrected” by Spencer at all.

    Now that it’s been published in full ( http://www.agu.org/journals/gl/gl1119/2011GL049236/ ), we can see that your asetions are indeed unmerited. A couple of sentences in the abstract/intro have been slightly altered (rather typical of the sort of “in-proof” alterations that scientific papers generally undergo), but the methods, results, interpretations and conclusions haven’t been altered. While several scientisits have been acknowledged for useful comments, Spencer isn’t one of these. He clearly didn’t add any insight whatsoever to the analysis.