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Lindzen Illusion #4: Climate Sensitivity

Posted on 5 May 2011 by dana1981

In his recent interview on an Australian radio talk show, Richard Lindzen discouraged the Australian public from implementing the country's proposed carbon tax.  One of Lindzen's main points in justifying this position was his favorite argument, "climate sensitivity is low."

"The crucial thing is sensitivity: you know, what do you expect a doubling of CO2 to do? If it's only a degree, then you could go through at least two doublings and probably exhaust much of your fossil fuel before you would do anything that would bother anyone."

"If we doubled CO2, it's well accepted that you should get about 1 degree warming if nothing else happened. [...] But 1 degree is reckoned as not very significant. The question then is: is what we've seen so far suggesting that you have more than that, and the answer is no."

Really, Dr. Lindzen?  "What we've seen so far" suggests that climate sensitivity is no higher than 1°C for a doubling of atmospheric CO2?  Sorry, but that's a load of baloney.

Lindzen and Choi 2009

Perhaps by "we," Lindzen refers only to himself and Choi, who published a paper in 2009 which examined sea surface temperature in the tropics and satellite measurements of outgoing radiation over very short timeframes, concluding that climate sensitivity to doubled CO2 is just 0.5°C.  However, the paper contained numerous fundamental flaws, and was soundly refuted by Trenberth et al. (2010), Lin et al. (2010), and Murphy (2010).  Even fellow "skeptic" Roy Spencer expressed no confidence in Lindzen and Choi's results.

Lindzen has acknowledged that the paper contains errors and has claimed that addressing them will not significantly change its results, which still show climate sensitivity less than 1°C for doubled CO2.  However, he submitted a revision over a year ago (February 2010), and it has still not been published, which suggests that the journal editors and reviewers were not satisfied with his efforts to respond to the criticisms.

Other Climate Sensitivity Estimates

Lindzen and Choi's paper is of course far from the only game in town in terms of estimating climate sensitivity.  In fact there have been dozens of studies on the subject using a wide variety of methodologies, including both climate models and empirical observational data.  Climate sensitivity has been estimated from paleoclimate data from millions of years ago, tens of thousands of years ago, the last few thousand years, the last few hundred years, from recent responses to large volcanic eruptions, to the solar cycle, and so on and so forth.  These different methodologies have all been consistent with a sensitivity likely between 1.5 and 4.5°C, with a most likely value close to 3°C for doubled CO2 (Figures 1 and 2).


Figure 1: IPCC climate sensitivity estimates from observational evidence and climate models

Various estimates of climate sensitivity

Figure 2: Various estimates of climate sensitivity (Knutti and Hegerl 2008).

And of course when we examined Lindzen's claim that "Earth hasn't warmed as much as expected" in Lindzen Illusion #1, and compared Lindzen and Hansen's temperature projections in Lindzen Illusion #2, in both cases we found that recent observational data is consistent with the IPCC's most likely climate sensitivity of 3°C, and inconsistent with Lindzen's purported sensitivity of below 1°C. 

Water Vapor and Clouds

Lindzen has been arguing for low climate sensitivity for a long time.  In an MIT tech talk Lindzen gave in 1989, he argued that two of the largest warming feedbacks, water vapor and clouds, are small or even negative.

"Water vapor is far and away the most important greenhouse gas, except for one form which isn't a greenhouse gas: clouds.  Clouds themselves as liquid water are as important to the infrared budget as water vapor. "

"In the current models, for reasons that puzzle almost everyone, the cloud feedbacks are positive rather than negative."

"On the planet the most wonderful constituent is water with its remarkable thermodynamic properties.  It's the obvious candidate for the thermostat of our system, and yet in most of these models, all water-related feedbacks are positive.  I don't think we would have existed if that were true."

Up to the mid-1990s, Lindzen believed the water vapor feedback could be strongly negative due to a drying of the upper atmosphere (i.e. Lindzen 1991, Sun and Lindzen 1993, Lindzen 1996).  However, in the late-1990s he began to change his stance on the water vapor feedback (i.e. Schneider et al. 1999).  And indeed, numerous recent studies using empirical observational data have confirmed the positive water vapor feedback.  For example, Dessler et al. (2008):

"Height-resolved measurements of specific humidity (q) and relative humidity (RH) are obtained from NASA's satellite-borne Atmospheric Infrared Sounder (AIRS)...The water-vapor feedback implied by these observations is strongly positive, with an average magnitude of λ q = 2.04 W/m2/K, similar to that simulated by climate models."

Thus Lindzen's over 20-year-long argument for low climate sensitivity really depends on the cloud feedback being strongly negative, more than offsetting the positive water vapor feedback (and other positive feedbacks like decreasing albedo from melting ice).  So in 2001, Lindzen put forth his "adaptive infrared iris" hypothesis (Lindzen et al. 2001) in which he proposed that increased sea surface temperature in the tropics would result in reduced cirrus clouds and thus more infrared radiation leakage from Earth's atmosphere, creating a cooling effect.

However, the iris hypothesis has not withstood the test of time (i.e. Fu et al. 2001Hartmann and Michelsen 2002, Lin et al. 2002).  A number of recent studies have also been incompatible with a strongly negative cloud feedback (i.e. Chang and Coakley 2007, Eitzen et al. 2008, Clement et al. 2009, and Lauer et al. 2010).  Perhaps the most convincing study thus far on the subject is Dessler (2010), which attempted to calculate the short-term cloud feedback using measurements by the Clouds and the Earth’s Radiant Energy System (CERES) instruments from March 2000 to February 2010. 

Dessler concluded that the short term cloud feedback is 0.54 ± 0.74 (2σ) W m-2 K-1, i.e. far more likely to be positive than negative, although negative values can’t be ruled out based on this data.  However, a small negative feedback is insufficient to support Lindzen's hypothesis that clouds will offset the other positive feedbacks and keep climate sensitivity below 1°C for doubled CO2.

Reality Check

Frankly, Lindzen's claim that "what we've seen so far" suggests sensitivity is no higher than 1°C for doubled CO2 could not be further from the truth.  In reality, nothing credible we've seen so far suggests sensitivity is nearly as low as Lindzen claims.  It's no wonder that Lindzen focuses so strongly on this argument, since climate sensitivity is the "skeptic" endgame, but as tends to be the case, the scientific evidence is not on Lindzen's side.

Once again, we find that Lindzen has been consistently wrong over the past two decades.  It's unfortunate that as Australians are trying to determine whether and how to address the threats posed by global warming and climate change, Lindzen chose to misinform them with a number of factually incorrect statements.

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Comments 1 to 18:

  1. Lindzen and Choi's 2010 paper, or at least an initial version of it (Feb. 2010), is available via this link. Upon reading it, they are still calculating strictly upon tropical data, using a simple geometric extension of tropical insolation to the rest of the globe, and still do not address heat transfer in/out of the tropics, which is considerably larger in magnitude than their feedbacks (one of the Trenberth criticisms). For example, "We argue that feedbacks are largely concentrated in the tropics and extend the effect of these feedbacks to the global climate." It appears to be a rehash of their 2009 paper, without any significant extensions, or for that matter, significant replies to the many criticisms. I can see why it hasn't been published yet.
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  2. Thanks KR. Indeed the revision was submitted over a year ago and was never published, likely for the reasons you describe.
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  3. Bernhard I have a question, not for any solution, just out of being interested, or maybe to see there might be ways out if mankind was for once behaving sane. Maybe somebody has done a calculation on how many trees needed to be planted (considering they need a few years before they really accumulate) and/ or how much biomass had to be turned into charcoal to be added to the exhausted soils to improve soils and store carbon. Would an attempt like this be able to do any significant change to the mounting level of co2 in the atmosphere, considering there is limited space to plant, but on the other hand we could plant using all the "useless" back- and front yards and so on, most of them only a waste of fuel as they are mowed week by week. And using whatever space that is not needed for food.
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  4. Bernhard, Look at wikipedia and the US EPA for info on your question. But according to the EPA, for example, one study showed that pine in the SE USA sequesters roughly one metric ton of carbon per acre per year (Birdsey 1996). Since the USA alone generates 5.8 billion metric tons of carbon per year, you would need to plant 5.8 billion new acres to offset our emissions completely (understanding, too, that at a point the trees would stop growing, so their sequestration abilities would diminish over time, although you'd get at least 50-100 years out of the project). And then you have to hope no one changes their mind and cuts down (or nature burns down) the new forests. But since the total area of the USA is only 2.45 billion acres, if you succeeded in planting trees absolutely everywhere, leaving no stone unturned, you'd still get less than half way there.
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  5. And, of course, much of that 2 billion acres is already forested, so you can hardly plant trees on the trees.
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  6. Why do I get the feeling that Dana's demolition of Lindzen is akin to squashing a bug by dropping an aircraft carrier on it? The weight of evidence is almost horrifically one-sided, and it's sonewhat sad that Lindzen keeps publically pushing the meme, and frustrating that he is doing so very publically. Well done Dana for another excellent article, and yet another great resource for literature on climate sensitivity.
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  7. thanks skywatcher
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  8. I may have missed it, or misunderstood something fundamental about the LIndzen approach, but has he ever been asked, or addressed voluntarily, the obvious question - if cloud negative feedback is so effective then how did climate change markedly in the past? Or does the iris effect only swing into action when the human release of CO2 causes an enhanced greenhouse effect?
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  9. I'm not sure how to answer that, David. I agree, it's a fundamental flaw in the low sensitivity argument.
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  10. Thanks dana, not just me then! My last sentence of course was both rhetorical and sarcastic.
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  11. Skywatcher, It is unfortunate that what Lindzen says is important simply because he so often quoted by skeptics and denialists in the mainstream radio and press. In Monktons article in the Australian he exclusively referred to Lindzen (effectively denying that anybody else has any expertise in CO2 sensitivity). In the latest edition of Quadrant (a right-winger favourite) there is an article that refers to Lindzen as THE expert on CO2 sensitivity. Essentially these publications deny the existence of the other scientists who have published on CO2 sensitivity, and they wonder why they get called denialists rather than skeptics.
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  12. It is worth noting that with Lindzen does not agree well, and some skeptics - as noted Sk.S. and behind them other blogs Well, the climate sensitivity is a problem " in itself". Uncertainties are large - Another look at climate sensitivity, Zaliapin and Ghil, 2010: “... for example in response to large increases in greenhouse gases or to other major changes in the forcing, whether natural or anthropogenic. This latter problem requires global interdisciplinary efforts and, in particular, the analysis of the entire hierarchy of climate models (Schneider and Dickinson, 1974), from conceptual to intermediate to fully coupled GCMs (Ghil and Robertson, 2000). It also requires a much more careful study of random effects than has been done heretofore (Ghil et al., 2008). It seems to us that Roe and Baker’s title question “Why Is Climate Sensitivity So Unpredictable?” still remains open. (This paper is a reference to: Hannart, Dufresne and Naveau: Why climate sensitivity may not be so unpredictable, 2009.) Could also add the problems with: the probability ... and one more note about clouds - do not forget about paper: Is There a Missing Low Cloud Feedback in Current Climate Models? Stephens, 2010.: “The consequence is that this bias artificially suppresses the low cloud optical depth feedback in models by almost a factor of four and thus its potential role as a negative feedback. This bias explains why the optical depth feedback is practically negligible in most global models (e.g., Colman et al., 2003) and why it has received scant attention in low cloud feedback discussion.”, because: “An analysis by Prof. Graeme Stephens in the article on page 5 suggests that solar radiation reflected by low clouds is significantly enhanced in models compared to real cloud observations. This finding has major implications for the cloud-climate feedback problem in models.” However, for most skeptics are not out of the clouds - the climate sensitivity on the doubling of CO2 - are the main problem, and GPP: Terrestrial Gross Carbon Dioxide Uptake: Global Distribution and Covariation with Climate, Beer et al. 2010.: “Most likely, the association of GPP and climate in process-oriented models can be improved by including negative feedback mechanisms (eg, adaptation) that might stabilize the systems.” Let me remind - here - the papers: The ecological role of climate extremes: current understanding and future prospects, Smith, 2011. i Effect of soil moisture and CO2 feedbacks on terrestrial NPP estimates - about a possible revaluation - here - certain positive feedback - in the IPCC models. That is why in the latest computer models - the summarizing RF for doubling of CO2 - less than 2 degrees K. 'Greener' Climate Prediction Shows Plants Slow Warming, Lynch - NASA, 2010. And even allowing that: “The range of feedback coefficient is determined by climate system memory. The longer the memory, the stronger the positive feedback. The estimated time constant of the climate is large (70 ~120 years) mainly owing to the deep ocean heat transport, implying that the system may be not in an equilibrium state under the external forcing during the industrial era.”
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  13. "In the current models, for reasons that puzzle almost everyone, the cloud feedbacks are positive rather than negative." This is a gem. Yes, back in 1989, it was a puzzlement. Yet, most recently, measurements have born out the results of whatever early models Lindzen was referring to. I'm referring to the post on this site, "What is the net feedback from clouds?", and in particular Dessler (2010), "A Determination of the Cloud Feedback from Climate Variations over the Past Decade". Lindzen's concern was valid in 1989, but it no longer carries the weight it once did. David H, indeed, the disagreement between the paleologic record and Lindzen's model has been raised before, but likewise, I haven't heard of a Lindzen explanation.
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  14. David, Chris, Lindzen's explanation for the ice age climate changes is that they were forced by changes in the distribution of solar forcing (orbital changes) to which he believes the climate system is much more sensitive that it is to changes in mean solar forcing (or mean CO2 forcing). Here's a representative piece (including a reply by Hoffert and Covey): That note (from 1993) has no actual calculations in it, and in this day and age it ought to have been trivial for someone to have built a simplified GCM with low climate sensitivity, and to see whether it is capable of producing an ice age. That no one has done so suggests that it's not possible to come up with a consistent model that reproduces the earth's observed behavior, and has climate sensitivity as low as Lindzen proposes.
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  15. dankd - Thanks for the link to the correspondence. Given that one of the major criticisms of Lindzen and Choi's various papers has been the lack of consideration of energy exchanges with the subtropics, his appeal to such "dynamic heat exchanges" to critique CO2 sensitivity is rather appalling - a severe case of the pot calling the kettle black. In particular, he states (quite correctly) "...given that the Earth's major greenhouse gas, water vapor, varies greatly with latitude and altitude, it is impossible to calculate the net greenhouse effect without knowing where heat is deposited by the dynamic heat transports." This sounds like a repeat of many of the L&C criticisms. And yet his 2010 revision (17 years after this correspondence) of the L&C paper completely ignores this issue! Very sad - personally, I can no longer take his work seriously.
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  16. Dankd, Thanks, my own searches were narrowing down to a debate that took place in Nature between Lindzen and Covey, circa 1993. I found this reference, but I haven't been able to find a link to the article. Lindzen, R. S.: 1993, 'Paleoclimate Sensitivity', Nature 363, 25-26. referenced in PALEOCLIMATE DATA CONSTRAINTS ON CLIMATE SENSITIVITY: THE PALEOCALIBRATION METHOD I'm thinking that Lindzen's argument that there will be meridional gradient pattern differences between orbital forcings and CO2 forcings has some merit. But, I get the impression that he obfuscates between the meridional gradient and the forcings which would cause it to change. Hadley cells are predicted to expand under CO2 forcing; so, that would also cause changes where Lindzen predicted none. But that is a cursory read of your discussion link, and I haven't found the actual Lindzen article yet. Another thought I have is that Lindzen's part of the discussion appears to be an argument of uncertainty. Again, it may have been valid at the time.
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  17. So, just pure Milankovitch with no CO2 contribution?
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  18. "... still show climate sensitivity less than 1°C for doubled CO2." How much less, may I enquire? We've already had 0.8C for a 'mere' 40% increase in ppm CO2. By my reckoning, less than 1C must mean 0.97, 0.9, 0.85, 0.88, 0.85. Looks to be coming up pretty soon. Probably before 50% increase in concentration. Has anybody ever asked him directly how he could explain getting past 1C increased temp with 50% or less increase in CO2 concentration? (Even 60 or 70%.)
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    [DB] "Has anybody ever asked him directly how he could explain getting past 1C increased temp with 50% or less increase in CO2 concentration?"

    It's a kind of magic...

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