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The carbon dioxide theory of Gilbert Plass

Filed under: — gavin @ 4 January 2010

Gilbert Plass was one of the pioneers of the calculation of how solar and infrared radiation affects climate and climate change. In 1956 he published a series of papers on radiative transfer and the role of CO2, including a relatively ‘pop’ piece in American Scientist. This has just been reprinted (as an abridged version) along with commentaries from James Fleming, a historian of science, and me. Some of the intriguing things about this article are that Plass (writing in 1956 remember) estimates that a doubling of CO2 would cause the planet to warm 3.6ºC, that CO2 levels would rise 30% over the 20th Century and it would warm by about 1ºC over the same period. The relevant numbers from the IPCC AR4 are a climate sensitivity of 2 to 4.5ºC, a CO2 rise of 37% since the pre-industrial and a 1900-2000 trend of around 0.7ºC. He makes a lot of other predictions (about the decrease in CO2 during ice ages, the limits of nuclear power and the like), but it’s worth examining his apparent prescience on these three quantitative issues. Was he prophetic, or lucky, or both?

To understand if Plass should get full credit, we need to see his workings. These are mainly outlined in two more technical papers in Tellus and QJRMS earlier that year. In today’s parlance, Plass calculated the change in top-of-the-atmosphere (TOA) radiative fluxes given a doubling (or a halving) of CO2 while everything else stayed the same. He then took that number and using someone else’s estimate of the sensitivity of the TOA radiation to the surface temperature, he calculated the temperature change that would be necessary to compensate. Converting from the units he used, the radiative flux values for a doubling of CO2 were 8.3 W/m2 and 5.8 W/m2 for clear-sky (no clouds) and averagely cloudy conditions (all-sky) respectively (and slightly larger and of opposite sign for a halving). The sensitivity of the TOA flux to surface temperature he used was around 2.3 W/m2 per ºC (equivalent to a temperature sensitivity of 0.4 ºC/(W/m2)). However, this is a ‘no-feedback’ estimate (allowing only the surface temperature to change with a constant lapse rate, but with no changes to water vapour, albedo or clouds).

Today, our current best guess for the forcing due to 2xCO2 is around 4 W/m2, and the ‘no-feedback’ sensitivity is around 0.3 ºC/(W/m2), giving an expected no-feedback temperature change of about 1.2 ºC, a factor of 3 smaller than the number Plass quoted, though since our number is for ‘all sky’ conditions, it would be a little better to compare it to his averagely cloudy number 2.5 ºC (so a factor of two higher). Note that Plass was a little casual in how he described his numbers and the ‘clear sky’ designation for the 3.6ºC number was not always made clear. However, Plass was well aware that the ‘no-feedback’ case was unrealistic and estimated that the water vapour, cloud and ice-albedo feedbacks would be amplifying, although he was not able to quantify them.

Moving now to the rate of change of CO2 in the atmosphere, Plass made a very good estimate as to how much human emissions of CO2 were increasing. His estimate was (again, in modern units) that then-current emissions were 1.5 GtC based on earlier estimates from Callendar, which actually was an underestimate. Our current best estimate for the anthropogenic emissions in 1956 is about 2.2 GtC. Given the increasing nature of the emissions, Plass then estimated that concentrations would rise about 30% by the end of the 20th Century. This however needs an estimate of how much of the emissions would be absorbed by the oceans and biosphere. Here, Plass has another impressive insight that the ocean chemistry would prevent quick uptake of the human CO2, a concept that wasn’t fully worked out until Revelle and Suess’s paper in 1957 (though possibly he may have been aware of some informal communications earlier). Plass actually assumed that none of the CO2 would be taken up in the short term. So his 30% growth estimate (the actual rise was 36%) was derived from an underestimate in emissions (and emissions growth) combined with an overestimate of the ‘airborne fraction’ (which is roughly 40% of total emissions).

Finally, his estimate of temperature rise of about 1ºC by the end of century follows from the two previous numbers, along with two further assumptions – that the climate is always close to equilibrium with the forcings and that of course, there aren’t any other factors changing. The first assumption affected by the substantial lag in the system because of the thermal inertia of the oceans, and of course, there are many more factors driving climate change over the 20th C. Plass can of course be forgiven for not knowing about the greenhouse impact of rises in CH4, N2O and CFCs (not realised until 1974), or the role of aerosol emissions (1970s), and indeed, he was fortunate that the net effect of all non-CO2 drivers is close to zero (though with significant uncertainties).

So Plass was correct about all of the big issues, but lucky that, in his quantitative estimates, the errors went both ways and end up pretty much cancelling out.

Eli has described this using Isaiah Berlin’s Hedgehog and the Fox metaphor – Plass being the Hedgehog who knows one big thing, and for whom the details are more incidental. I think this is a reasonable take, as long as it is realised that Hedgehogs are not always right, even though in this case he was.

The Fox in this case was another big name in atmospheric physics, Lewis Kaplan. He published a counter to Plass’s 1956 work in Tellus in 1960 (vol. 12, p204-208), and there was a “spirited” exchange of letters in 1961 (vol. 13, p296-302) (references for those of you with libraries – for some reason, none of the old Tellus volumes are online). His calculation used a different methodology, more up-to-date spectra but was different enough in approach and specifics to make a fair apples-to-apples comparison between the results hard to do. Nonetheless, Kaplan declared that “Plass’ estimate of a temperature drop of 3.8ºC due to a halving of [CO2] appears to be too high by a factor of two or three” and that “it would seem, then, that CO2 variations could not play a role in the ice-age cycle unless the changes were by an order of magnitude”.

The subsequent comment and reply are actually very reminiscent of recent disputes in climate science. Plass complains that not enough information was provided to replicate the analysis, that Kaplan used unjustified precision, that he wasn’t comparing like-with-like (all-sky with clear-sky), that he made unjustified technical assumptions, and that his overall conclusion was ‘misleading’ because of the neglected feedbacks (that neither of them had quantified). Kaplan responds that of course there is enough information to check his workings (in another paper), that it was Plass’ fault he compared the all-sky and clear-sky numbers, and that he has exaggerated the impact of the technical criticisms. Notably, Kaplan did not respond on the issue of feedbacks.

Looking over the exchange with a 50 year perspective, a number of things stand out. First, Kaplan does seem to have been closer to modern values in his calculation – Plass was out by a factor of two for the all-sky no-feedback case. I’m not really familiar enough with the details to be be able to tell why (perhaps someone can enlighten us in the comments). However, Kaplan was wrong about everything that has ended up mattering – CO2 does play a big role in ice age cycles (with a magnitude of change close to what Plass anticipated) and its growth today is climatically significant. Significantly, I can find no trace in the literature of any resolution of the technical issues raised in the letters. Resolution in Plass’ favour of the big questions came with further independent efforts as computers got fast enough to do the more complicated feedback problem, better observations, better spectral data and better paleo-climate information (particularly from the ice cores). In some sense, resolution of their technical differences would have been moot because that wasn’t the real issue. Of course, that would have been difficult to see at the time.

So, to summarize, Plass did have some key insights and in many respects was well ahead of his time. But he was also lucky.

Update: Stay tuned, it looks like there is another little wrinkle to this story…

158 Responses to “The carbon dioxide theory of Gilbert Plass”

  1. 51
    Ray Ladbury says:

    Dean Weichmann, I am not merely being kind when I tell you that you have made an astute observation. Near the Antartic coast, where temperatures are a bit milder, you might well get more evaporation, which, when it falls inland, will fall as snow. Thus, you expect melting at the edges and growth inland–which is what we see. Keep in mind, though that the situation is not simple wrt ice flow, etc., and exactly what happens depends on the temperature profile locally, prevailing winds, etc..

  2. 52
    Daniel C. Goodwin says:

    Congratulations on a classic post, Gavin. Seriously: you are a great explainer, like Feynman, and like Spencer Weart. The human story of how science shakes into place can be a great bridge to scientific understanding; the best antidote to the anti-science tenor of the times.

    Speaking as a confirmed hedgehog, I find Gilbert Plass’s story inspirational. Thanks so much, everyone.

  3. 53
    Edouard Bard says:

    Re 32.

    Here is the link to the PDF of the full thesis by Jean-Louis Dufresne: A large part is in English but not (yet) the introductory sections.

    Note also that the thesis was evaluated by three independent « rapporteurs » (including a foreign colleague from the UK) and four « examinateurs ». It has thus passed a stringent peer-review process. I know that Jean-Louis Dufresne is busy translating this historical part in order to submit it to an international journal. That would imply a second round of peer-review. However, you are right in saying that peer-review is necessary, but not sufficient.

    You can thus read the thesis and its demonstration, but it is already clear that the one layer greenhouse model is inadequate to reproduce the temperature change due to a CO2 increase because a description of the vertical temperature gradient is required. Using such an oversimplified model leads to an underestimation of the warming. This point has already been underlined in previous RC posts (including “A saturated gassy argument, Part 1 and Part 2”). In addition, Arrhenius used absorption measurements from Langley that do not include the important CO2 15-micron absorption band, and part of the absorption by H2O is attributed to CO2. This was the information available at this time, but this led to a warming over-estimation cancelling the other bias.

    Arrhenius also hypothesized that ice ages were caused by falls in the atmospheric CO2 content. In the very same 1896 paper, he uses observations of geologists on the displacements of the snowline and concluded that temperatures were 4-5 ◦C colder during the glacial period. According to his greenhouse calculations, this generalized cooling could be explained by a CO2 fall of about 40%. Hence, Arrhenius got it amazingly right for both the glacial temperature and CO2 drops: his 1896 figures are compatible with what we know today from modern paleoclimate proxies (including CO2 measured in bubbles from Antarctica ice cores). The problem is that we also know that the glacial cooling is not mainly due to CO2 forcing which represents only a quarter of the total radiative perturbation during the glacial period (-2 compared to -8 W/m2, see Fig. 6.5 page 451 of IPCC 2007 AR4).

    As I underlined in my previous comment (#19), the point is not to blame Arrhenius who was working with the information available at his time. As a scientist interested in the history of his field, I think it is important to realize that our heroes are indeed true heroes, but also that an additional century of science has improved our knowledge on the relationship between global temperature and atmospheric CO2. This was the point of my 2004 article cited in your comment and that can be downloaded from the following web page:

  4. 54

    #41 Alan of Oz

    I miss the preview button too :(

    I amke more mistakes without it ;)

  5. 55

    #51 Dean Weichmann, Wisconsin

    No worries, it’s a good question when sincere.

    In addition to #52

    My current perspective is considerate of the reality that while increases in snowfall can and do occur on a region to region basis, mid latitudes will see that snow melting faster, plus, when Antarctica, sometime in the future, reaches it’s tipping point and the inertial trend is melting rapidly, sea level rise will move much faster on the relative geologic time scale. As of now it’s a fight between accumulation and calving at the edges.

    Generally speaking though, I think it is safe to assume we will see in the future, the number of entire towns and cities or even regions being shut down by large snowfall increasing. I think that has already begun though but as always you can’t say a single event is climate because it can be weather.

    I tend to characterize it as motion in the trends. Certainly the headlines of late are showing this may be true.

  6. 56
    Josh Cryer says:

    Alan of Oz, excellent Asimov essay, I hadn’t seen it before. :) I’d also add this YouTube video:

  7. 57
    Stuart says:

    Plass writes:
    The latest calculations show that if the carbon dioxide content of the atmosphere should double, the surface
    temperature would rise 3.6 degrees Celsius and if the amount should be cut in half, the surface temperature would fall 3.8 degrees.”

    Is it known precisely what model and assumptions Plass used to obtain these numbers?

    Why are his numbers different than the numbers reported here which utilize MODTRAN spectra not available to Plass in 1956:

    One method of estimating the contri­bution made by the presence of CO2 to the total 34·5°C of global warming is by the use of the MODTRAN programme and database, which contains all the spectral information about greenhouse gases and allows the calculation of fluxes at any alti­tude, looking downwards to the surface or upwards towards space.

    Keeping everything constant except for the CO2 concentration and consid­ering the transfer of energy across the troposphere at an altitude of 15 km, the results of Modtran calculations are shown in the graph. For each point the temperature was reduced until radiative balance was re-established.

    The widely proph­esied doubling in CO2 concentration from the pre-industrial value of 285 ppmv to 570 ppmv would be associated with an increase of just 1·5°C.

  8. 58
    Matthew says:

    55, Edouard Bard, Which of your articles are in English?

  9. 59
    John E. Pearson says:

    59: The link you posted to is the only skeptic site I’ve ever seen that didn’t make me want to tear my hair out. I hate to jump to quick conclusions but I think these guys are actually honest. They take a minority view point on climate sensitivity arguing that it is lower than the IPCC estimates (which have been roughly consistent for roughly 30 years since the Charney report but they also debunk an enormous amount of standard denialist nonsense. It was refreshing.

  10. 60
    Edouard Bard says:

    Re 60 “Which of your articles are in English?”

    The paper cited by #32 is Greenhouse effect and ice ages: historical perspective. C.R. Géosciences 336, 603-638, (2004). This is a bilingual article which English section starts on page 616.

    On the same web page, there are several other review papers available for download (EPSL 2006, Physics Today 2002) which you might find useful.

  11. 61
    François Marchand says:

    Re 52sq : Mount Kinabalu (Malaysia) is situated roughly on the Equator, at an elevation of 4000 m +. It never snows there, ever wondered why?

  12. 62
    Rattus Norvegicus says:

    John @60, Stuart @59:

    Wouldn’t the value you found be a lower bound on the doubling of CO2? It seems that if you keep everything else constant, then you are ignoring the water vapor feedback, which is likely of a similar value as the straight CO2 contribution. In you experiment the final value would be: 3.0C!

  13. 63
    CM says:

    sidd (#37),
    Thanks for taking me up on an offbeat question! I’m afraid your Drude reference went over my head, though…?

  14. 64
    Don Shor says:

    Schmert says:
    “a concept that wasn’t fully worked out until Revelle and Suess’s paper in 1957″
    So there really was a Dr. Seuss ?

    Well, yes. Hans Suess, Roger Revelle, and Dr. Seuss (Theodor Seuss Geisel) all lived contemporaneously in La Jolla, CA.

  15. 65
    sidd says:

    Re: Drude

    he made a famous (to physicists) pair of errors in in solid state physics. Briefly, he didn’t have Fermi-Dirac statistics so he used the classical Maxwell-Boltzmann distribution which led to errors in specific heat and counterbalancing errors in mean velocity for electrons. So i made another idle suggestion that you might like to see where he was trained.

    More important, he was a competent scientist who made an educated derivation based on the knowledge of his time. Which is why we still study his derivations. As with Arrhenius and Plass and perhaps with all scientists. No one knows everything, but the point is to avoid the ‘not even wrong’ arguments. This is not possible without a deep and extensive grounding in the universe of discourse, usually gained in grad school.

  16. 66
    Brian Dodge says:

    “Mount Kinabalu (Malaysia) is situated roughly on the Equator, at an elevation of 4000 m +. It never snows there, ever wondered why?” François Marchand — 5 January 2010 @ 3:50 PM
    “The white blotches on the ground in this photo are pockets of snow, just below the summit of Kinabalu.”

    With a lapse rate of ~5.5deg/km, a height of 4100 m, and a temperature range of 20-36 deg C (
    and “with temperatures rarely ever falling below 30 deg C”( near sea level, snow is rare, and doesn’t accumulate.

  17. 67
    Norman says:

    With all the very cold weather around the Northern Hemisphere at this time, I had a thought of a way to prove a precise degree carbon dioxide actually warms air (dry air with no water vapor like cold polar air or hot desert). The current method does require a lot of assumptions and seems more like a work or Art than a precise scientific formulation.

    The Surface area of Earth is 5.1*10^8 km^2

    I have read that the Global Temperature is based on around 3000 recording stations and most of those are concentrated in the developed world. If you would grid those 3000 recording stations around the Earth one station would cover an area of 170,000 km^2 Huge area with lots of variable temps within.

    I have read how you take some nearby stations and estimate what the temperature is in the areas without stations. Looking at Air mass temperatures of the Earth on a daily basis…

    Air mass temps look like they have many odd shapes and it looks like it might be a real guess to get temps for these unknowns. There are circular masses, tounges, boxes etc.

    The precise calculation I can think of would be to determine the theoretical adiabatic cooling rate of air with no water vapor or greenhouse gasses. Just oxygen and nitrogen. This will be the control. The rate given for adiabatic cooling is around 10 C per 1000 feet. The contribution of warming from carbon dioxide would decrease the adiabatic cooling by exactly the rate at which it can absorb the radiation from the ground below and heat the rising parcel of air. The more carbon dioxide in the air parcel, the lower should be the cooling relative to air with no carbon dioxide to absorb ground radation and warm.

    The change in rate would give an exact measure of the heating contribution of carbon dioxide outside all the other influences that impact Global Temperatures.

  18. 68
    Richard Brenne says:

    Thanks Andy (#1 and #2) for the links including that great Frank Capra video. While at UCLA film school I corresponded with Capra over a period of years, but never about that.

    We probably all agree that Lindzen is the most credentialed of all the global warming deniers, but while he has many awards and recognitions, they are a tiny fraction of those won by those who disagree with him and ge generally agree with Gavin, the vast majority of IPCC scientists, etc.

    This from Wikipedia’s entry for Richard Lindzen:

    Lindzen has been characterized as a contrarian. Lindzen’s graduate students describe him as “fiercely intelligent, with a deep contrarian streak.”

    This characterization has been linked to Lindzen’s view that lung cancer has only been weakly linked to smoking. Writing in Newsweek, Fred Guterl stated “Lindzen clearly relishes the role of naysayer. He’ll even expound on how weakly lung cancer is linked to cigarette smoking. He speaks in full, impeccably logical paragraphs, and he punctuates his measured cadences with thoughtful drags on a cigarette”

    Thus Lindzen has become more or less a hedgehog who is wrong about one big thing, while Fox news is a fox
    who is wrong about many things.

  19. 69
    Spaceman Spiff says:

    The link provided in #59 was, as already noted, a wonderful breath of fresh air in that it is an actual attempt to critique some of the conclusions of the 2007 IPCC report — scientifically, and at the same time points out the non-sense of the anti-science “arguments” blasted all over the blogosphere (and many media outlets).

    Their main conclusions seem to be that many of the climate sensitivity estimates may be too high — if still significant nonetheless (climate sensitivity = how many degrees C rise in temperature for a doubling of the CO2 concentration for an Earth in near radiative equilibrium). However, they’ve apparently concentrated at the results pertaining to radiative equilibrium with respect to the C02 concentration. Other than waving their hands about the effects of positive feedbacks (maybe they’re overestimated) and negative feedbacks (maybe they’re understimated), they really do not address these. Climate scientists are certainly aware that a good deal of the predicted climate sensitivity is due to a significant net feedback contributions. They might also keep in mind that there are several feedback mechanisms, some of them positive, that were not included in the models that ended up in the 2007 IPCC report (not to mention that everything that climate scientists know indicates that ignorance is not on the side of humanity).

    Nevertheless, a nice set of tutorials overall.

  20. 70
    Susan Anderson says:

    Great post and discussion.

    It is time that conclusions formed a long time ago and repeatedly confirmed, with great growth of understanding and a variety of inputs as well as obvious results (seasonal change, species migration (bugs not wintering over with chaotic results due to decreased cold), increased “weather” such as droughts in dry areas and floods in wet ones, and of course socioeconomic conflict over scarce resources where people are desperate) receive the attention they require and deserve. The 100s of times recycled arguments and techniques of doubt creation are doing humanity a severe disservice.

    With respect to cold in a warming climate, I think this is an issue that needs to be explained early and often. Bearing in mind that I am not a scientists but an artist – water vapor patterns are gorgeous – who got involved because of the handwriting on the wall over my lifetime, my opinions are subject to expert deconstruction. Nonetheless, one of the most frequent arguments against climate change due to global warming is the confusion over the word warming.

    Currently, we have an “arrow” of cold directly from the Arctic and I expect the usual arguments about local short-term “weather” are making the rounds on the propaganda wheels.

    On Antarctica and snow, there was recently an excellent article in The New Yorker on penguins, which unfortunately is behind a subscription wall, However, this excellent slide show is available. It mentions the above-explained phenomenon. In places where it is below freezing, of course even at increased temps increased water vapor is going to result in snow.

  21. 71
    Dan Lufkin says:

    Back in the early 1960s I was the USAF meteorological liaison officer at the Meteorological Institute of the University of Stockholm (MISU) (an assignment that dates back to the 1930s). Administratively I was a graduate student and took classes and did research with Bert Bolin’s nascent atmospheric chemistry department. My field is atmospheric optics and I joined a small group working on light scattering by aerosols (almost exactly the same thing Jim Hansen worked on in Leiden a few years later). The other side of the shop was working on greenhouse gases. Paul Crutzen was doing ozone and Dave Keeling had just arrived for a year’s stay as a Guggenheim Fellow with several years of CO2 observations from Mauna Loa.

    Everybody knows that the scattering thing looked good at first, but once you do the math, the greenhouse effect wins. I went ahead and finished my thesis on scattering polarization in noctilucent clouds with Bolin as my advisor, but by the time I was done, practically everyone at MISU was either working on CFCs and ozone or CO2 and greenhouse. We didn’t have much in the way of computing power in Stockholm then, so we were only a little ahead of Arrhenius (for whom the MISU building is now named; back then we were in tiny quarters on Lindhagensgatan that had been abandoned by the Microbiology Institute).

    I had to get back to the USAF in 1964 and went on to work more in scattering and then in satellites for 20 years. Just recently I was asked to teach a short course in climate change and took the occasion to put together a short paper on my time at the feet of Bert Bolin when all this stuff was just getting on a good scientific basis. If anyone’s interested, I’d be glad to send a copy. Let me know at

  22. 72
    Spaceman Spiff says:

    Let me clarify my post #71, pertaining to the Barrett and Bellamy web pages, that I would not at all be surprised if many of their critiques and conclusions have been taken to task by climate scientists. It’s just that up to now I have never encountered a critique of the 2007 IPCC report appearing in web pages that wasn’t completely worthless. This one at least makes the attempt to explain the science and uncertainties (from their point of view) to the non-expert.

    The signal to noise of most of the comments at RealClimate and other scientifically useful web sites (like Skeptical Science) would be a whole lot higher if discussions began at this level of understanding or better. And that’s the point I was trying to make.

  23. 73
    Joel says:

    I think a post about how the peer review process in climate science could be improved would be interesting to your readers.

  24. 74
    uncle pete says:

    For non US citizens. What’s a “beer bust ?” Sounds like fun.
    Plass musn’t have liked the amber liquid perhaps ?

  25. 75
    Edward Greisch says:

    53 Ray Ladbury: I have heard that the whole midwest becomes a desert, and the opposite. That the monsoon misses India and China completely in X years. Etc. I know that “the rain moved” has caused many previous civilizations to collapse.
    Do you know anything about where the rain is going to move that the rest of us don’t? Maybe this belongs in “unforced variations”, but I think that is over.

  26. 76
    Dave Ah says:

    If this is not the right place for learning the fundamentals I apologise for wasting your time and should be grateful to be referred to a better one. Perhaps unsurprisingly, I have been looking for a site to educate myself about the greenhouse effect. The explanations I have read up to now (eg do not satisfy me at all and to convince myself I have to be more concrete.

    In the past I have done a few simple engineering calculations, including fluid dynamics. I am familiar with time dependence, convection (what you call advection, I believe) and diffusion, but I have no experience at all of radiation. For my self-education I should like to be able to explore a number of simple and solvable model problems. The first one I have in mind would be a static atmosphere, invariant parallel to the Earth’s surface, which would initially be taken as plane. All quantities, including gas properties, would vary with altitude. (At present I am unsure whether conditions at the surface and at the top of the atmosphere might have to be treated as assumed data rather than emerging from the computations.) The equation of state (1) and the hydrostatic equation (2) will hold. I imagine the energy equation (3) will reduce to the onedimensional heat conduction equation, but with a distributed heat source encapsulating the greenhouse effect. I should like to evaluate the heat sources independently and to solve the three said equations in an uncoupled fashion.

    Is the above scheme a reasonable way to gain some understanding? If so, can any radiation theoreticians please tell me how to calculate the heat sources through the model atmosphere?

  27. 77
    Geoff Wexler says:

    Re #50

    [This is intended to be my last comment on glass greenhouses before everyone else becomes completely fed up with it].

    CFU ; as far as I can see you are saying that it would be almost impossible to use themostats to maintain my suggested boundary conditions * in the face of a near short circuit by convection. I shall ignore that for a moment, because it might perhaps be surmountable, but then I encounter a worse objection. What I dislike about this arrangement is its complex and unatural design. The natural circuit consists of short wavelength energy in through the glass balanced by long wavelength out, either by transmission or by re-radiation (the last bit ignored in the pop piece.) In my version this circuit would have to include the energy flowing in and out of the thermostats which would have to be monitored and might be the dominant energy flow. Hence I come back to…

    Simplified Conclusion: Plass’s remarks in the pop-piece about glass greenhouses would have been better replaced by one sentence saying that the transmission properties of CO2 are a bit like those of glass.

    [* i.e. the roof of the greenhouse held at the temperature of dy ice (or even liquid nitrogen) while the floor fixed at 20 degsC]

  28. 78

    Stuart–the difference is caused by the fact that the IPCC sensitivity includes feedbacks and your MODTRAN calculation doesn’t. You said everything was kept the same but carbon dioxide. The IPCC assumes that as carbon dioxide rises, so does water vapor, through the Clausius-Clapeyron effect. There are also land-ice albedo feedbacks, cloud feedbacks, etc.

  29. 79
    Stuart says:

    “Stuart–the difference is caused by the fact that the IPCC sensitivity includes feedbacks and your MODTRAN calculation doesn’t.”

    OK, but that wasn’t really my question. My question was – what was Plass’s original assumption? Obviously he didn’t have MODTRAN data. The original question posed by Gavin was – was Plass prophetic or lucky? So – did Plass also consider water feedback? Or was he just lucky to get the same answer as the IPCC a different way?

    As a secondary question on the water feedback – why does water not simply feedback on itself? No need to burn fossil fuels to get more CO2 here – there is an almost infinite reservoir of water available to create the greenhouse gas water vapor – so why doesn’t some heating occur due to some watre vapor – and then more water vapor feedbacks and so on? This would be a runaway affect. It obviously doesn’t happen – but why would doubling the CO2 suddenly make the water vapor contribution become larger?

    Furthermore, doesn’t the evaporation of water lead to cooling through the Joule-Thompson effect? If so, wouldn’t a doubling of CO2 create cooling through water evaporation – in other words a negative feedback mechanism?

    Really – are these Feedbacks properly understood? The graph in the Barret website I linked to for temperature versus CO2 seems to be uncontroversial – is that correct? So the argument is really not about CO2 but about the sign of feedback mechanisms – positive or negative?

  30. 80
    Completely Fed Up says:

    “My question was – what was Plass’s original assumption? ”

    If that was your question, why did you bring up MODTRAN?

  31. 81
    Jim Eager says:

    Stuart @81: why does water not simply feedback on itself?

    Think Stuart.

    What will happen if you add water vapour to the atmosphere without first warming the atmosphere?

    How would you get more water vapour to stay in the atmosphere without first making the atmosphere warmer?

    Now think a bit further.

    What does adding more CO2 to the atmosphere (or increasing insolation, or reducing albedo) do to the atmosphere?

  32. 82
    Geoff Wexler says:

    why does water not simply feedback on itself?

    It does and is included in the interpretations given in these comments (perhaps in the previous thread) . The water vapour concentration depends on the temperature. Lets repeat the argument. Assume that there is a small warming W degs.C; this warmed atmosphere holds an additional water vapour concentration proportional to W. Call it Wa. This will cause a further warming of Wab degs. C and the process will be repeated thus:

    W + Wab + W(ab)^2 +W(ab)^3 +…. = W/(1-ab)

    [where (ab)^2 = the square of ab]. Every term except the first consists of water vater vapour feeding back on itself. But you must have the first term to have a non-zero effect. Where does W come from? Answer from the growth of a greenhouse gas or the increase of incident solar energy. But if these are absent W = 0 and you can see from the right hand side that the net warming is zero.

    Your other question involves bookkeeping and terminology rather than feedbacks. If the total water vapour in the air increases it implies that energy has been transferred (its called latent heat) but it is not lost to the climate. The same point applies to melting ice. That too requires latent heat. These processes increase the effective thermal capacity (inverse climate sensitivity) but would be automatically included in any calculation.

    Nothing is perfectly understood, but that is a long way from arguing that David Bellamy or his colleague are right about down-playing all the evidence for a significant positive feedback.

  33. 83
    Geoff Wexler says:

    #49 Hank Roberts (off topic)

    though the search tool doesn’t handle arithmetic well, couldn’t find it again

    While we are on that topic, is there a simple way of searching for a given string through all the pages of a thread composed of many pages? I have a rather slow computer.
    P.S. I did not follow why you thanked me in the first part of the same message. Were you referring to someone else?

  34. 84
    Hank Roberts says:

    Stuart, I pasted your question in to Google.
    This is from the first page of results; maybe it will help. Make sure to click the “citing papers” links in the right sidebar as well.

    Isaac M. Held and Brian J. Soden

  35. 85
    Doug Bostrom says:

    “As a secondary question on the water feedback – why does water not simply feedback on itself? ”

    Dumb guess here, but water precipitates at a much higher temperature than does C02?

    “Furthermore, doesn’t the evaporation of water lead to cooling through the Joule-Thompson effect? If so, wouldn’t a doubling of CO2 create cooling through water evaporation – in other words a negative feedback mechanism?”

    Where would the heat go? Water evaporating at the bottom of the atmosphere does not mean the heat has left the planet.

  36. 86
    Ike Solem says:

    Stuart, the distinction between the water vapor ‘feedback’ and the carbon dioxide ‘forcing’ is simply related to the timescales of CO2 and H2O mixing – and since water vapor has a relatively short lifetime in the atmosphere compared to CO2 (weeks vs. decades) due to factors like evaporation, cloud formation and precipitation, they must be treated differently.

    Hence, a weather model tries to predict the specific short-term future of water vapor in the atmosphere (will it rain in a few days, or not?) while a climate model tries to get a picture of how time-averaged precipitation and evaporation will change due to the CO2 blanket, which has the largest effect in the mid/upper troposphere – which is what Plass discovered.

    See the guest post at RC by spencer &raypierre:

    Measurements done for the US Air Force drew scientists’ attention to the details of the absorption, and especially at high altitudes. At low pressure the spikes become much more sharply defined, like a picket fence. There are gaps between the H2O lines where radiation can get through unless blocked by CO2 lines. Moreover, researchers had become acutely aware of how very dry the air gets at upper altitudes — indeed the stratosphere has scarcely any water vapor at all. By contrast, CO2 is well mixed all through the atmosphere, so as you look higher it becomes relatively more significant.

    Now, this warm CO2 blanket radiates in BOTH directions after it is heated up by infrared radiation from the lower levels of the atmosphere and the Earth’s surface, right? Up and down. However, this blanket is also blocking the infrared from reaching the upper levels of the atmosphere – hence, we see stratospheric cooling associated with tropospheric warming. (Try getting that result from an increase in solar radiation!) We also see oceanic warming associated with tropospheric warming, but with a significant lag factor (hence, we’re in for warming for decades after CO2 levels have stabilized, which will happen, umm…. when?).

    So, that’s the essence of the problem. The complicating factors are many, most notably how this will change existing patterns of atmospheric and oceanic circulation. Take the ENSO phenomenon, for example – here is the latest anomaly data for the eastern Pacific:
    Central Pacific Ocean temperatures remain well above El Niño thresholds. Trade wind strength returned to near normal over the past fortnight, slightly reducing the excessive warmth of the equatorial Pacific Ocean. However, significant areas remain more than 2°C above average at the surface, and over 4°C warmer than normal at depth.

    However, the global weather patterns seem to be responding anomalously to this climate phenomenon, don’t they? One contributing factor appears to be the differential warming of land surfaces vs. ocean sea surfaces, with the land warming faster (as per long-standing climate model predictions) – and is this likely to create high pressure systems over continental subtropical regions, in places like Africa, Australia, South America, the American Southwest? Well – yes, that seems reasonable enough, doesn’t it? Wouldn’t that tend to dampen down the ocean influence a bit? Isn’t this the major concern of California weather forecasters – and couldn’t that explain the anomalously low rainfall in an El Nino year?

    At the same time, the CO2-forced warming of the ocean surfaces is resulting in an increase in water vapor in the atmosphere – and while the rough estimate (Soden & Held, etc.) is that wet areas will get wetter and dry areas will get drier, the day-to-day reality seems to point towards less predictability and more violent fluctuations – for example, the “1000-year” floods in Britain, etc. etc.

    P.S. This is an interesting quote, gavin:

    Some people do have a contrary nature – especially scientists – and in fact including me. It comes down to initially adopting a ‘show me’ stance when you see new ideas and trying to burrow down into the assumptions that might underlie it. In small does it comes in quite handy. However, this has to be tempered with an open mind that allows you to be persuaded by new information.

    You should consider applying that contrary “show me” stance to the ridiculous claims about clean coal carbon capture? “Show me a prototype” or “show me the energy demand per ton of captured CO2 relative to the energy generated per (~1/3) ton of coal?” (one ton of coal generates roughly three tons of CO2 upon combustion with O2?)

    It’s becoming more and more evident that the entire program is just cover for coal gasification, not for “zero-emissions power plants” but rather for coal-to-gasoline schemes. Oddly enough (or maybe not), transparency at the DOE over this issue has just plummeted – they’ve locked the doors on reporters and are now hiding “contractor performance reviews” on the issue from public scrutiny.

    When you start labeling scientific criticism as “political advocacy” and calling people “crusaders against DOE/Battelle” – ahem – you risk walking down that very path yourself. Just a friendly reminder – and I’m pleased to see that now Jeffrey Sachs has admitted that coal carbon capture likely won’t work for Battelle’s FutureGen Alliance projects, and neither will it work for Chevron and Exxon’s LNG plans in Australia and Papua New Guinea.

    This clean coal business is not a matter of political failure – it is something far worse, institutional failure within the U.S. science system itself – ten years of nonsense with no peer review at all! And Stephen Chu of LLNL is still claiming that he sees “no fundamental problem” with the approach. “Collegiality issues” have kept other scientists at LLNL from saying anything about it – but if that’s not Lysenkoism in action, what is? When is enough enough?

    Of course, if someone can build a working prototype of a zero-emission coal combustion system that generates more energy than it sucks up – and which sequesters carbon in a geologically stable format – I’ll happily eat crow – but I’m not holding my breath, considering the basic thermodynamic barrier. I’m still astonished that the notion ever gained any ground at all – but that’s the politicized DOE for you. They need to be restructured as an independent scientific agency – all they are now is a funding conduit/PR agency for fossil fuel and military-industrial contractors.

  37. 87
    Shirley says:

    @Dean Weichmann, #51… I think your question has been pretty well answered, but I’d like to add some food for thought on weather and glacial dynamics. Glaciers which form on land masses aren’t flat, so incoming air behaves much as it does as it moves towards mountains. Something called orographic lifting occurs which is a fancy way of saying air goes up as it approaches the mountain slope. As the moist air rises, it cools, condenses and precipitates, on that side of the mountain. As on temperate land, the other side becomes a “rain shadow desert” so the profile of the ice mountain takes on a skewed appearance. To get an idea of what I mean, you can use Google Earth and go to Baffin Island. Find the biggest white mass on it, and draw an imaginary line across it and look at the elevations. You should be able to guess from which direction the prevailing winds come. (note that the elevation data in GE should be considered as estimations only; I have found a lot of inconsistencies with it and don’t consider it to be accurate, but good enough for an exercise like this)

    On that note, some more food for thought: while wind patterns globally tend to trend certain ways, they are also dynamic (ie: El Nino). Therefore, whether or not an area gets more or less precipitation has a lot to do with whether or not the area from which the air is coming (moist or dry) and at what direction relative to the topographic features. My point is that whether or not Antarctica, which is HUGE, will get more or less snow has more to do with prevailing winds, although you are correct in assuming that warmer air can and does hold more moisture.

    Now a little about glacial dynamics… snow falls on top of an existing glacier and by adding its weight, it cumulatively increases the pressure below it. A lot of everyday people don’t realize this, but glacial ices moves like a plastic substance. Because the pressure at the top is less than at the bottom of the glacier, the greatest/fastest movement is in the lower portion of the ice. In other words, the weight of additional accumulation causes spreading below, and how quickly the ice moves depends on how cold that ice at depth is. This is well known from bore holes drilled into the ice, and the bottom shifts much more quickly than the upper portions. So at warmer temperatures, you could theoretically have a large area of thin ice vs. thick ice covering a lesser area in colder temperatures. This is an oversimplification, but my point is that ice that covers a geographically large or small region may not have the expected mass just by looking at how much land it physically covers. This is something NASA’s ICESAT satellite is working on: how to quantify the actual mass.

    One of the many issues some scientists are looking at now is how to better understand how ice at depth responds to changes in temperatures, temporally and by depth.

    As you can see, there are numerous complicated factors to consider when thinking about when or why one area may or may not receive more precipitation, whether or not glaciers will grow, and a definition of what “growth” really is.

  38. 88
    Ernst K says:

    “As a secondary question on the water feedback – why does water not simply feedback on itself?”

    Umm, it does. But the effect is limited by the fact that water vapour readily condenses and falls as rain/snow. In a big picture sense, adding in some more CO2 –> warmer atmosphere –> water doesn’t condense as readily –> more water water vapour in atmosphere –> warmer atmosphere –> loop again.

    You can think of it as CO2 enhancing the existing water vapour feedback.

    “Furthermore, doesn’t the evaporation of water lead to cooling through the Joule-Thompson effect? If so, wouldn’t a doubling of CO2 create cooling through water evaporation – in other words a negative feedback mechanism?”

    Perhaps it’s just me, but what does evaporation have to do with the Joule-Thompson effect? In case you just used the wrong name, evaporation of water is part of the energy balance at the surface. A water molecule evaporates when it gains energy from some combination of the surface, the air, and incoming radiation. It is a key factor controlling how energy moves between the land, ocean, and atmosphere but evaporation itself doesn’t cool or warm the Earth as a whole.

    I like to use money analogies for water/energy budget questions, because most people can relate to monetary budgets. If I give you a $100 bill, as a group do we become richer or poorer?

  39. 89


    Yes, Plass considered water feedbacks–as did pretty much everybody from Arrhenius on.

    [Response: No he didn’t. He knew they existed, but they were not part of his calculations. That would have to wait for Moller and Manabe a decade later. – gavin]

    As to why there’s no runaway water feedback, magnitude matters crucially. In the abstract, feedback needs to attain a critical threshold to “run away”–else the effect damps out at some new equilibrium level.

    Understanding of feedbacks is both complicated and a work in process, but quite a lot is known about them, too.

  40. 90
    Completely Fed Up says:

    “You can think of it as CO2 enhancing the existing water vapour feedback.”

    I would put it more as

    CO2 STARTING the water vapour feedback.

    Same thing for methane et al.

    Gavin, I would suspect that if the ONLY Greenhouse gas in the atmosphere was H2O we would now be frozen with almost no H2O in the atmosphere.

    Would that be right?

    You have to make a fake earth that “eats” any other GG, to stop volcanoes pumping it out…

  41. 91
    Stuart says:

    My question on water feeding back on itself was mostly rhetorical, since it obviously doesn’t happen or else there would already be a runaway situation. Barrett claims that water evaporation does indeed cool the surface.

    The admittedly simple energy budget model of the atmosphere/surface system described on this website suffices to demonstrate what might be the case if water did not have the possibility of cooling the surface by evaporation. The surface temperature of 288.8 K would rise to 301 K without the cooling effects of water. The extra radiative forcing arising from the doubling of CO2 would cause an increase of surface temperature of 2.6 K assuming it to be doubled by the positive radiative feedback from the extra water vapour, but this is reduced to 1.5 K if the water cooling is allowed to operate. These figures are rough-and-ready, but indicate the significant effect of the water cooling feedback which seems to be absent from the more sophisticated models used to predict future climate.

  42. 92
    Ernst K says:

    “I would put it more as

    CO2 STARTING the water vapour feedback.”

    OK, perhaps we’re just looking at this a little differently. For me, it’s easier to grasp the basics of feedback by considering how we go from old equilibrium to old equilibrium + disturbance to new equilibrium.

    So we have a totally dry Earth with no H2O but enough CO2 that the average temperature is well above 0 deg C.

    Now, add some (OK, lots) water. As the water evaporates, and H20 enters the atmosphere the air temperature increases (quite a bit, based on my understanding of the trace gas effect). The increased temperature enhances evaporation and increases the concentration of water vapour which leads to more warming. Keep looping until you reach a new equilibrium. I would call this a water vapour feedback process, and it’s still with us today, it just is (was?) more or less in equilibrium.

    Now, of course, condensation means H20 reaches its equilibrium much faster than other trace gasses so the feedback wouldn’t be as obvious, but the feedback is still there.

  43. 93
    Shirley says:

    Gavin, I think you’ve done a great service by bringing the work of Plass and others to light. Far too many people believe that nothing was known about climate before the 1980s, or worse. Getting stories like this out there could really help people understand that the current theories and revelations in climate science aren’t just wild ideas that popped up in a fad-like fashion. People need to understand that all the work being done now is built upon the work others began decades ago, with each and every researcher adding to the vastness of knowledge. I’m looking forward to the next “wrinkle” you’ve set up as a tease!

  44. 94
    Shirley says:

    Barret & Bellamy lost me on the “Warming Controversy” page, which in addition to being very simplistic and incomplete for such an important topic, also makes this statement:

    “We should mention that in the early seventies some climatologists were predicting the onset of a cooling period, possibly leading us into the next iceage. The same set of people are today predicting ‘dangerous’ warming. In the last three years there has been a cooling of the planet”

    Sorry, but I can’t help but roll my eyes when anyone brings up the cooling hype of the 70s. I put it right up there with the bunk “List of 30,000 Scientists…” people bring up and expect to be taken seriously. I’m further disturbed by the statement that warming is now purported by “the same set of people” which is extremely misleading, and makes me wonder how he defines his other sets. Granted, the site is not nearly extreme as others, but I have to call that out as an outright distortion, which immediately makes me distrustful of anything else they have to say. And as with anyone, I want to know where they get their funding.

  45. 95
    Geoff Wexler says:

    Ike Solem #88

    Your comment is good as usual. Just one point. I think it includes the same error about the cooling stratosphere as I made when I first started reading this subject. Gavin told me I was wrong, and I eventually chose an explanation I liked based on one of Raypierre’s comments. This is how I see it now:

    You wrote :

    However, this blanket is also blocking the infrared from reaching the upper levels of the atmosphere

    Yes that was also my original explanation for the cooling. But even if true this is the weakest of several effects. In the troposphere there is an energy balance between convection, infrared (IR) absorption and IR emission. In the stratosphere on the other hand there is another big term i.e absorption of short wavelengths mainly by ozone. The IR emission is still substantial because the temperature is considerably higher as a result of this heating. The IR absorption is not enhanced by this heating however because it is determined mainly by up-coming IR. So the IR absorption plays a much less important part than it does in the troposphere. So it is not a big deal if the IR coming up from below is reduced by increasing the greenhouse (gh)blanket. The more important effect here is the enhancement of the gh emissions from the same cause.

  46. 96
    Ernst K says:

    “The extra radiative forcing arising from the doubling of CO2 would cause an increase of surface temperature of 2.6 K assuming it to be doubled by the positive radiative feedback from the extra water vapour, but this is reduced to 1.5 K if the water cooling is allowed to operate.”

    OK, this is just silly. GCM models definitely consider the effect of evaporation from the Earth’s surface, and they do it in a far more accurate and sophisticated way than the “admittedly simple energy budget model” does.

  47. 97
    Ernst K says:

    Oh, I hate this. I forgot to paste in the following key sentence from Stuart@93:

    “These figures are rough-and-ready, but indicate the significant effect of the water cooling feedback which seems to be absent from the more sophisticated models used to predict future climate.”

    This is the silly part.

  48. 98
    Ernst K says:

    Isaac M. Held and Brian J. Soden

    In that paper, I found the following:

    “For a balanced view, it is useful to watch an animation of the output of such a model, starting from an isothermal state of rest with no water vapor in the atmosphere and then “turning on the sun,” seeing the jet stream develop and spin off cyclones and anticyclones with statistics that closely resemble those observed, watching the Southeast Asian monsoon form in the summer, and in more recent models, seeing El Nino events develop spontaneously in the Pacific Ocean.”

    I don’t suppose anyone has a link to such an animation?

  49. 99
    Hank Roberts says:

    Good point from Ike Solem:
    > coal gasification, not for “zero-emissions power plants”
    > but rather for coal-to-gasoline schemes. … transparency
    > at the DOE over this issue has just plummeted

    Someone’s been doing scenario planning at Defense, I bet.

    Remember how the US committed to uranium rather than thorium fission, thus guaranteeing as a ‘side effect’ a source of large amounts of refinable plutonium.

    The “just in case we need it for, er, something else we don’t want to talk about” justification makes bad choices.

  50. 100
    Doug Bostrom says:


    “The surface temperature of 288.8 K would rise to 301 K without the cooling effects of water. ”

    Do the authors suggest a means of transport of heat away from the planet, once it has been moved from liquid water to water vapor? There’s something missing in the explanation, but perhaps the authors account for that?

    Think of it this way: you’ve got a wet blanket in an insulated room. As the blanket evaporates water, the temperature of the blanket drops but the total energy content of the room remains the same. The room’s insulation knows nothing about where the heat is stored inside the room. Meanwhile, eventually the air will become saturated, thus ending the “cooling effect”. The entire system will only actually cool as heat can escape through the insulated walls.