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Lindzen Illusion #6: Importance of Greenhouse Gases

Posted on 10 May 2011 by dana1981

Throughout the Lindzen Illusions series, we've gone back and scrutinzed his 1989 MIT Tech Talk to evaluate how Lindzen's climate positions in 1989 compare to his beliefs today, and to observational reality.  In the talk, Lindzen made a statement about greenhouse gases (GHGs), downplaying the importance of carbon dioxide (CO2):

"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.  Both swamp by orders of magnitude all the others.  With CO2 one is talking about three watts per square meter at most, compared to a hundred or more watts per square meter for water."

Similarly, in a 1992 article, Lindzen said:

"Even if all other greenhouse gases (such as carbon dioxide and methane) were to disappear, we would still be left with over 98 percent of the current greenhouse effect."

It's worth noting that this is one of Lindzen's previous positions which has gone by the wayside.  Lindzen still believes that water vapor and clouds play key roles as feedbacks (which is true, although he has the magnitude and sign of those feedbacks wrong, as we saw in Lindzen Illusion #4), but he no longer downplays the significance of CO2 in the greenhouse effect.  However, "water vapor is the most powerful greenhouse gas" has become one of the more popular climate myths, and remains pervasive among "skeptics", so it's worth once again examining the validity of this argument.

Schmidt et al. (2010)

This issue was addressed by two recent papers from NASA GISS, Lacis et al. (2010) and Schmidt et al. (2010).  Schmidt et al. examined the contributions of various GHGs to the Earth's greenhouse effect.  Schmidt et al. concluded as follows:

"we find that water vapor is the dominant contributor (∼50% of the effect), followed by clouds (∼25%) and then CO2 with ∼20%."

Schmidt et al. estimate the global mean longwave radiative flux from CO2 at  approximately 30 Watts per square meter (W/m2), clouds at 40 W/m2, and water vapor at 80 W/m2. This is a stark contrast to Lindzen's 1989 claims:

"With CO2 one is talking about three watts per square meter at most, compared to a hundred or more watts per square meter for water."

Lindzen claimed that water vapor and clouds contribute at least 30 times more to the greenhouse effect than CO2, but as Schmidt et el. show, the ratio is closer to a factor of four.  On this issue, Lindzen was off by an order of magnitude because he underestimated the CO2 radiative flux by a factor of ten.

Similarly, Lindzen claimed without GHGs other than water vapor and clouds, "we would still be left with over 98 percent of the current greenhouse effect."  In reality, water vapor and clouds account for approximately 75% of the greenhouse effect.

Lacis et al. (2010)

Lacis et al. answer the question of "the most important GHG" even more directly.  In fact, the first sentence in the abstract of their paper reads:

"Ample physical evidence shows that carbon dioxide (CO2) is the single most important climate-relevant greenhouse gas in Earth’s atmosphere."

The authors note that unlike water vapor, CO2 does not condense and precipitate from the atmosphere at current climate temperatures.  Unlike many other greenhouse gases such as CO2 which can be added to the atmosphere, the level of water vapor in the atmosphere is a function of temperature.  If extra water is added to the atmosphere, it condenses and falls as rain or snow within a week or two.  In short, water vapor is a feedback, not a forcing.  NASA GISS summarizes the results of Lacis et al. (2010) as follows (emphasis added):

"Because carbon dioxide accounts for 80% of the non-condensing GHG forcing in the current climate atmosphere, atmospheric carbon dioxide therefore qualifies as the principal control knob that governs the temperature of Earth."

So when it comes to governing global temperature changes, Lindzen's statement is backwards.  CO2 plays a much larger role than water vapor and clouds, which act to amplify the CO2-caused warming, but don't remain in the atmosphere long enough to drive global temperature changes themselves.

A Lindzen History

As noted above, this is one of Lindzen's 1989 climate beliefs which has gone by the wayside, but unfortunately, remains a fairly widespread belief amongst global warming "skeptics".  Once a climate myth is born, it's very difficult to kill, as the Skeptical Science Arguments database shows.

In the next Lindzen Illusions installment, we'll examine the history of Lindzen's climate arguments - what he argued in 1989, what he argues today, what is necessary for his arguments to be correct, and how those requirements stack up against observational reality.

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Comments 51 to 61 out of 61:

  1. scaddenp: No, my point is that in the real world of climate Schmidt's paper is pretty much irreverent. dana1981@50: Yes, in the lower atmosphere it appears to be. Upper atmosphere? It doesn't appear to be.
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  2. Camburn @51, I don't know what Schmidt's religious decorum has to do with anything ... More seriously, we know you are trying to assert the irrelevance of Schmidt's paper. What you have not done is provide any reason to consider it so. The best you have come up with so far is that you are more interested in the result Lacis et al than in Schmidt et al. Fair enough. Each to their own; but your personal preference has no bearing on whether Schmidt et al asked an interesting question and answered it effectively. The question in fact may not be interesting of itself, but has been made so by the frequent false assertions by deniers that CO2 has an inconsequential greenhouse effect. The answer was effective because it was clear, and derived in the only practical way to do so. It also gives every indication of being rigorous within the current limits of modelling.
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  3. Camburn,
    my point is that in the real world of climate Schmidt's paper is pretty much irreverent.
    You have pretty decisively failed to prove a single point. You have failed to grasp even the basics of his paper. Your posts amount to casting aspersions and declaring that things are not what they are. Schmidt's paper takes a simple problem -- a subset of the much larger problem -- in trying to tease out the individual contributions within the atmosphere to radiative warming of water vapor, clouds and CO2, within the "starting point" 1980 climate regime. It does so using complex physics based models that you do not understand, and which you have grossly oversimplified in your own mind. He comes up with results that are reasonable, and trustworthy within the current limitations of climate science. Lindzen's entire position, on the other hand, is comically and cosmically ridiculous. He has made no effort to support it, and it is in fact so flawed in so many ways that deconstructing it is trivial. He makes a child's argument, hoping that the childish will fall for it. He operates, as you do, simply by declaring things, without supporting evidence or complete understanding (although in this case, his demonstrated ignorance is an intentional convenience). Your ability to arbitrarily declare the study inadequate, "fixed," or anything else does not detract from the validity of the science. It merely detracts from the validity of your contribution to the discussion.
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  4. Tom Curtis @ 52: I don't know where religion entered here, but if you think Schmidt is religious or not religious, that is your perogative. Sphaerica: I understand the model run quit well. His paper does not tease out the individual contributions of water vapor, clouds, etc. It holds those fixed while changeing one dynamic....which is co2. The study isn't inadequate, and I have never stated that. I stated that in the chaotic climate that is not fixed, the results of this study do not apply. He has used h20 vapor as a positive forcing. The data from both balloons and satillites concerning this issue has such a large error bar that it, at this time, is unreliable. That is why I posted the paper that links to this. Anyways, thanks for the discussions and pointers. I learned one thing, I will not use slab as a description again as it seems to raise red flags and offend some. That was not my intent.
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  5. 54, Camburn,
    It holds those fixed while changeing one dynamic....
    For the last time, you have this 100% wrong, and you will be stalled in your understanding of climate science until you abandon your Wattsian belief system and start to figure out what is really going on.
    I stated that in the chaotic climate that is not fixed, the results of this study do not apply.
    I had not seen this statement, but... why on earth would it not apply? First, the climate is not (normally) chaotic. Weather is chaotic, but the climate, without forcing, does not vary by more than ± 0.3˚C, and within that, I would doubt that the percent contributions of water vapor/clouds/CO2 vary by much, if at all. In fact, I would doubt that the percentages vary much even in a more chaotic climate, however that remains to be seen/studied/proven.
    He has used h20 vapor as a positive forcing.
    No. This is more Watts-speak, and comes from your misunderstandings of models. If nothing else, please review the links at the end of this post. But in a nutshell, most models (and modelE in particular) are physics based. One does not set parameters. One does not say "I will declare that H2O feedback will be +3.53". They program in the absorption bands of H2O, and the specific heat, and the parameters surrounding evaporation, etc., etc. They let it run, and H2O does whatever it does under the physics programmed into the model. The fact that all of the models (programmed by different people using different methods and different assumptions) demonstrate the same behavior is one confirmation that they have it right. The fact that real world observations demonstrate very similar behavior in various resulting outputs is another confirmation. The fact that their final global mean temperature of the planet matches reality is another confirmation. Beyond this, models are not just run once. They are run multiple times, with variations in parameters and random events, so that an ensemble average can be computed. This stuff isn't done in a vacuum, and it's not done just by setting parameters. Please read: FAQ on climate models FAQ on climate models: Part II It is also highly recommended that anyone interested in climate science take the time to read Spencer Weart's The Discovery of Global Warming. It is a very easy read, very, very informative, and provides a great foundation for understanding the current state of the science, regardless of whether or not you agree with current conclusions about climate change.
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    Response:

    [DB] Fixed text.

  6. 54, Camburn, Just to follow up, for more info on models, see these specific sections in Spencer Weart's pages: Simple Models of Climate Change General Circulation Models of Climate Both of these are very, very informative, and more importantly, they don't so much tell you what the results are as how they are achieved. There is nothing arguable or partisan about the topic under discussion. These pages simply provide a wonderful view of the depth, scope, complexity, evolution and current state of climate models. If you read this, you will have a much better understanding of Schmidt et al 2010, and everything else that is based on climate modeling.
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  7. Camburn @54. Ignore the comment about religious demeanour. It was a pun based on your mistyping of "irrelevant". I should have known better.
    "I understand the model run quit well. His paper does not tease out the individual contributions of water vapor, clouds, etc. It holds those fixed while changeing one dynamic....which is co2."
    From Schmidt et al:
    "In one set of calculations, we remove the radiative effects of each major absorber in turn (water vapor, clouds, CO2, CH4, N2O, CFCs, ozone, aerosols), and then in the second set, we only use each individual absorber, thus defining the minimum and maximum impact of each radiative constituent (Table 1). For each absorber, both short‐ and long‐wave effects were used or removed simultaneously, though we focus on the LW impacts here. We also performed a number of combination experiments..."
    Clearly you do not understand what was done. You claim that all factors where held constant, and just CO2 removed. What Schmidt et al actually did was hold everything constant, and remove the effect of H2O and run the model; then restore H2O, and remove clouds and run the model; then restore the clouds, remove the CO2 and run the model; and so on. They then repeated the whole procedure except that they kept in just one element, and removed all the others - one by one. By doing this, to the extent that the model is accurate, they determine the TOA forcing of the entire system with circa 1980 climatology but without each component, one at a time and the same climatology but with just one component for each component. And just for good measure, they ran some combination experiments in which they removed or retained groupings of components of the system. Granted that this is a model, and has whatever inaccuracies are inherent in that. But we cannot, after all, actually remove all the CO2 in 1980 to see what happens. However, given that limitation, how else could you possibly determine the relative effect of each component of the atmosphere than by the method used by Schmidt et al? That is a serious question. If you don't like that methodology, propose a methodology that would improve on it. I'm betting that you cannot; and I'm betting that because what Schmidt et al looks pretty much like text book procedure to me. In the end, your objection merely comes down to a claim that in the real world, if you removed all the CO2 (or H2O, or clouds) you would not retain the circa 1980 climatology. The claim is true but irrelevant. That does not preclude the determination of relative effect in a 1980 climate. It only means the determination once made is of theoretical rather than practical import. Your objection then, comes down to either pure obscurantism; or a bizarre insistence that only questions in which you are interested in are allowed to be answered, ie, that because you are not interested in the theoretical issue addressed by Schmidt et al, therefore any attempt to answer it is flawed.
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  8. Part of the appeal of the Schmidt and Lacis et al papers is how "public friendly" and explicit they are in focusing on a topic which is of blogosphere interest. As for "how relevant" they are, Schmidt et al. specifically noted that they were motivated by a need for a reference concerning the attribution of the greenhouse effect into its individual components. If it is not relevant to understanding climate sensitivity, or further understanding anthropogenic climate change, it is only because they never claimed it to be. I'm not entirely sure the papers, especially Lacis et al (2010), said anything which hasn't been presented in the literature before (e.g., Kiehl and Trenberth 1997, Pierrehumbert et al., 2007; Voigt and Marotzke, 2009)so I don't think it should have been passed along as an original research paper. But it does help to reinforce rather well-understood physics details, and there should be nothing inherently surprising in the results. The experiment done by these papers is rather straightforward: The terrestrial greenhouse flux attribution calculations reported in Schmidt and Lacis et al. are for a current (year 1980) climate & atmospheric structure, with TOA outgoing fluxes recalculated after each constituent is added one-by-one to an empty atmosphere, or removed from the full atmosphere. The radiative transfer is done very accurately with the correlated k-distribution method of Lacis and Oinas (1991). Concerning the water vapor feedback, the trends reported in the cited Paltridge et al paper are highly spurious, based on data unsuitable for what they attempted to do (see e.g., Trenberth and Fasullo,, 2005; Soden et al 2005). Dessler and David (2010) further showed that the conclusions of the Paltridge paper are unique to that specific reanalysis set and is not robust to other choices of reanalysis sets.
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  9. Has anyone seen the peer reviewed article that seems to be suggesting TSI is close to six times greater than previously estimated for solar max and minimum?
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    Response:

    [DB] You'll have to provide more info than that.  Publication, author, title, year is usually the minimum.  Direct link is best when you want an opinion on a paper.  Thanks!

  10. I think you mean this one: Shapiro, et al. 2011. Someone pointed it out to me a couple days ago, thinking it proved the sun was responsible for the current warming. I'm not in a position to judge their methodology, but their results don't seem to me to contradict the idea that the sun isn't responsible. They show that the output from the sun has been pretty flat for the latter half of the last century, so it doesn't seem that the sun could be causing the current warming (at least from their results - and the paper says explicitly that their results don't deviate from previous results for the more recent data). I assume that this would call into question the climate sensitivity, but since that's never been given an exact number, that doesn't seem too earth shattering. I would be interested in seeing someone more qualified comment on it, but all I could find from Google was comments from the blogosphere, and it's hard to lend credence to anything there.
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  11. 60, SteveS, Interesting paper. I haven't gone through it yet, but it gives barely a nod to temperature and climate, and makes no statement at all beyond "the climate warming during the steady increase in solar activity in the first half of the twentieth-century." It seems they're just trying to use proxies (sunspot counts, and tree rings and ice cores) to compile a more precise record of TSI and SSI prior to the existence of adequate instrumental observations (last 30 years) back to 1600 (based on proxy data availability). If someone wanted to read into it, though, I think you're right in saying that it can't explain post 1950 warming. Really, if anything, it helps disprove solar influence. Looking only at their graphs as compared to temperatures, the implication is that increasing TSI through the first half of the 20thcentury could account for the warming in the first half of that century, as well as some reason for the leveling of temperatures starting around 1950, but then cannot account for the warming in the last 30 years. But in the end, the paper isn't about climate change at all. It's just about coming up with a new and hopefully better interpretation of proxy measurements to establish TSI and SSI back to 1600.
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