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Is the CO2 effect saturated?

What the science says...

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If the CO2 effect was saturated, adding more CO2 should add no additional greenhouse effect. However, satellite and surface measurements observe an enhanced greenhouse effect at the wavelengths that CO2 absorb energy. This is empirical proof that the CO2 effect is not saturated.

Climate Myth...

CO2 effect is saturated

"Each unit of CO2 you put into the atmosphere has less and less of a warming impact. Once the atmosphere reaches a saturation point, additional input of CO2 will not really have any major impact. It's like putting insulation in your attic. They give a recommended amount and after that you can stack the insulation up to the roof and it's going to have no impact." (Marc Morano, as quoted by Steve Eliot)

If the CO2 effect is saturated, adding more CO2 should add no additional greenhouse effect. However, observations continue to find an enhanced greenhouse effect as CO2 levels rise. The paper Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997 (Harries 2001) attempts to find out. In 1970, NASA launched the IRIS satellite that measured infrared spectra between 400 cm-1 to 1600 cm-1. In 1996, the Japanese Space Agency launched the IMG satellite which recorded similar observations. Harries 2001 compared both sets of data to discern any changes in outgoing radiation over the 26 year period. The resultant change in outgoing radiation was as follows:

Figure 1: Change in spectrum from 1970 to 1996 due to trace gases. 'Brightness temperature' indicates equivalent blackbody temperature (Harries 2001).

What they found was a drop in outgoing radiation at the wavelength bands that greenhouse gases such as CO2 and methane (CH4) absorb energy. The change in outgoing radiation over CO2 bands was consistent with theoretical expectations. Thus the paper found "direct experimental evidence for a significant increase in the Earth's greenhouse effect".

This result has been confirmed by subsequent papers using the latest satellite data. Griggs 2004 compares the 1970 and 1997 spectra with additional satellite data from the NASA AIRS satellite launched in 2003. Chen 2007 extends this analysis to 2006 using data from the AURA satellite launched in 2004. Both papers found the observed differences in CO2 bands matched the expected changes based on rising CO2 levels. Thus we have empirical evidence that increased CO2 is preventing longwave radiation from escaping out to space.

Measurements of downward longwave radiation

What happens to longwave radiation that gets absorbed by greenhouse gases? The energy heats the atmosphere which in turn re-radiates longwave radiation. This re-radiated energy goes in all directions. Some of it makes its way back to the surface of the earth. Hence we expect to find increasing downward longwave radiation as CO2 levels increase.

Philipona 2004 finds that this is indeed the case - that downward longwave radiation is increasing due to an enhanced greenhouse effect. Evans 2006 takes this analysis further. By analysing high resolution spectral data, the increase in downward radiation can be quantitatively attributed to each of several anthropogenic gases. The results lead the authors to conclude that "this experimental data should effectively end the argument by skeptics that no experimental evidence exists for the connection between greenhouse gas increases in the atmosphere and global warming."

So we have multiple lines of empirical evidence for an enhanced CO2 greenhouse effect. Satellite measurements confirm that less longwave radiation is escaping to space. Surface measurements detect increased longwave radiation returning to Earth at wavelengths matching increased CO2 warming. And of course the result of this energy imbalance is the accumulation of heat over the last 40 years.

Intermediate rebuttal written by dana1981

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Last updated on 26 October 2016 by pattimer. View Archives

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Further reading

V. Ramanthan has written a comprehensive article Trace-Gas Greenhouse Effect and Global Warming.

Further viewing

Video by Rosh Salgado on his "All about Climate" YouTube channel in which he debunks Will Happer's claim that the CO2 effect is saturated in the atmosphere:


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Comments 1 to 25 out of 715:

  1. My apologies for what is in effect a repost, but I asked this question at the bottom of a second page of comments where I first saw this diagram. Here I can be first :-) (and I think it's a relatively important question) There is one thing that bothers me about figure 1 (the differential spectrum). The decreased emission in certain absorption bands makes perfect sense. But it's a fact of the (surface) instrumental record that the planet was (a little) warmer in 1996 than in 1970 (somewhere in the 0.1 to 0.2C range). So shouldn't the flat parts of the differential spectrum be just a bit above zero? I suppose it's possible due to different instruments (i.e. different satellites) that they had to normalize, but it would have been so much better if they didn't. Does anyone have the answer?
  2. I suppose it's also possible that the satellites were in more-or-less low equatorial orbits, were thus only measuring the tropics, and the tropics have seen the least surface warming. Ok, I'm out of ideas for the moment.
  3. What I don't understand about this argument is that we have a clear demonstration of what high levels of CO2 can accomplish in respect to greenhouse effect with Venus. From what I understand Venu's atmosphere is over 95% CO2 and it's surface tempuratures are almost 500 degrees celcius. That makes it hotter than Mercury the closest planet to the Sun. If CO2 had a saturation point wouldn't Venus have reached it or am I totally misunderstanding the premise?
  4. GFW, as I understand it, Figure 1 shows outgoing radiation. Therefore, if the Earth has warmed, more radiation remains inside, i.e., less radiation goes out. Therefore, the net outgoing radiation must be below zero (less radiation going out, i.e. radiation that remains inside the atmosphere, in a transient radiative imbalance, until the earth warms enough as to "expel" again the same energy that comes in, going back to equilibrium (at zero) but with a higher temperature given that the greenhouse blanket is now thicker). In this graphic the different wavelengths are differenciated, so we can see which exact wavelengths are being trapped inside (those that are below zero), i.e. the exact wavelengths that are responsible for the warming inside. The rest of wavelengths escape to space the same as before (the components for those wavelengths have not changed, so the same energy goes in and out), and that's why they are at zero level. rlasker3, I think you are perfectly right. If the CO2 saturated, we woudn't see that runaway greenhouse effect in Venus.
  5. Your half correct PeterPan The figure in this article is out going radiance but is only part of the actual figure from the Harris 2001 paper. It has been manipulated to highlight the drops in radiance CO2 and CH4. I'm not trying to suggest dishonesty it's just a way to present the data. In the 'real' data the 0 point is actually lower, you can see this in the publication. So what you have comparing 1970 and 1996 is reductions in radiance at the C02 and CH4 positions but increases in radiance in the areas in between. I've never seen any good explanations for the changes at these other wavelengths. Or seen any reasoning behind highlighting the spectra in the CO2 and CH4 regions and ignoring the rest of the spectra. My own explanation would be that while there is increased energy retention at the wavelengths absorbed by CO2 and CH4 there are also other changes which are allowing more energy to escape at different wavelengths. I have no problem with suggesting that this paper identifies a signature in the radiance data for an increase in CO2 in the atmosphere but without complate analysis of the spectra (which the publication doesn't do) you can't conclude that this is leading to warming
  6. i thought venus's atmospheric pressure has a lot to do with its temperature?
  7. Wouldn't a much more useful test of a saturation point be, testing for a saturation point? This only seems to directly indicate that if there is such a saturation point, we haven't hit it yet, not that there is no saturation point to hit. I haven't been able to find anything to this effect, but a test in a laboratory using a similar method to observe the absorption rate of the same wavelengths passing through a chamber with various concentrations of the gasses we would expect to see in the upper atmosphere could show whether it does have an asymptotic behavior and thus 'saturates'? Just seems somewhat fishy that the logic goes "It could reach a saturation point!" "But it's still increasing as we increase the CO2, so there is no saturation point!", analogous to "If you eat too much candy you get sick!" "But I've been eating candy for the last 20 minutes and I continue to feel fine!"
  8. NkThrasher, that has been done. A long time ago, and repeated with increasing precision and thoroughness right up to currently. See the post How do we know CO2 is causing warming?; in that post, look in the green "Acknowledgements" box just above the start of the Comments section. Click on the link "laboratory measurements...".
  9. What do you make of this claim? I haven't read it thoroughly, but it seems like they are missing the fact that CO2 is absorbed at several different wavelengths. The post devolves into the usual questioning of motives, but I was curious to hear thoughts on the main claim about the 14.77 micron band being used up. Thanks, M
  10. mazibuko, the problems with those guys is that their reasoning looks straightforward and anyone can understand it. The mistake he makes becomes apparent only if you know the physics. So common people tend to trust those bogus falsifications. The problem with that "falsification" is not just related to the single band he considers, he arbitrarly put a limit to the amount of radiation CO2 can absorb. This is not true both experimentally (as shown in this post) and theoretically even for the 15 micron band alone; and it would not matter anyway.
  11. Hi Riccardo, Thanks for the answer and links. I have trouble enough keeping on top of the literature in my own field, so it is very useful to come to a place like this and have someone with a good knowledge of the particular issue provide/point me to a summary. I saw a good clip on Richard Dawkin's TV today about how to spot baloney, which is perhaps apropos to this matter. One common form of baloney occurs when someone claims that his/her theory shoots down an existing and better understood theory, based on falsifying only one particular aspect of the better understood theory. The new theory, however, can't explain all the other phenomena that are explained by the better understood theory. Thus, the notion that all the multiple lines of evidence for a human forcing on climate can be falsified because all those silly (and agenda-driven!) scientists overlooked CO2 saturation seems to qualify as baloney. Thanks again, M
  12. NkThrasher #7: the whole concept of saturation is based on a misconception of how radiation is passed up, level by level, through the atmosphere. Spencer Weart has some good non-technical descriptions of this, which I've adapted here.
  13. hey guys, i think you should all look at Dr. Ferenc Miskolczi's theory on the saturated effect of greenhouse gases. you can download his paper for free on scribd. . i would love it if you guys have a look at it and get back to me.. because it looks very very convincing.. so if someone can have a look at the math involved and see if its all legit that would be excellent.. here is the link to the summary report of his findings aswell; He says that the climate models used by the ipcc are based on old math from the 1920's which make an assumption that the atmosphere is infinitly large.. he redoes the math with proper boundary conditions and comes up with very interesting results.. i'll leave it up to you guys to look further into it email me on if you'd like to send me your thoughts if youd prefer that than this comment cheers
  14. qball17 #13 That's not a proper scientific paper, it's a paper from the partisan Science and Public Policy Institute (home of among others the rather badly discredited "Lord" Christopher Monkton, and the australian geologist Bob Carter). If there was any merit in the presentation/summary that you printed, then it would be easy for him to publish in a reputable scientific journal. So you have to ask the question why hasn't he? The papers cited at the top of this page are a much better source for you to form your opinions from.
  15. qball17, Miskolczi's "paper" is well known and badly flawed. As Eli at Rabett Run ironically puts it, his theory could be summarized in just two sentences: "The greenhouse gas theory that has been used for the last century is TOTALLY WRONG! The proof is left as an exercise for the reader.".
  16. so the atmosphere is infinitely large is it? so what is the better model? can you show me some solid evidence that debunks the saturated greenhouse effect and proves that CO2 drives climate?
  17. the reason why he couldn't publish it was because NASA refused to let him, so then he went back to hungary and made his paper.. just like all the other scientists who say how hard it is to get a scientific journal published that is against or is skeptical about anthropogenic climate change. Don't you find it funny how all the readily available journals are CO2 CO2 CO2.. how can science come up with such a definite conclusion with all the other factors that would contribute.. this issue has turned into a political one, not scientific... how do these papers justify the CO2 lag behind temperature, and solar activity etc etc
  18. and by the way.. the title of this topic is ridiculous.. its not the "saturated Co2 effect", its the "saturated GREENHOUSE effect".. we all know that we can increase the concentration of CO2.. what about the work from Dr. Nicola Scafetta?
  19. and another thing.. he did publish it in hungary. Dr. Miskolczi first published his work in the Quarterly Journal of the Hungarian Meteorological Services in 2004, Volume 108, No 4. He published further statistical proof in the same Journal in 2007, Volume 111, No. 1. In the 5 years since he first published his results, not one peer review has come back disproving his theory, or his Constant. To date, not one scientist has come forward to disprove Miskolczi’s theory that the Earth’s climate is at equilibrium, and that Carbon Dioxide cannot be released in amounts great enough to upset that equilibrium.
  20. you should have a look at the following link and see what you think.. it also has a link to his 2004 paper which people don't look at, that is why they get confused and see his paper as making too many assumptions etc.. its because 2007 paper is the sequel to his 2004 paper where he defines many of his terms and comes up with the science behind the theory
  21. qball17, please refrain from nitpicking, and refrain from using over-the-top terms such as "ridiculous." You might also read more carefully, and when something doesn't make sense, consider the hypothesis that you might not be parsing it correctly; the title is "Is the CO2 Effect Saturated?," which to most readers parses correctly as "Is the CO2-Effect Saturated?" As for Scafetta, scroll down to the link to his paper in this post: It’s the sun.
  22. Hi How can these guys be right “Falsification of the Atmospheric CO2 greenhouse effect within the frame of physics” by Gerhard Gerlich and Ralf D. Tscheuschner , Ive beeen looking for rebuttals to there paper but now luck so far can anyone help ? thanks Dave
  23. Hi ok ive realised from google searching that someone is posting this in just about any blog they can and by the body of the post it seems to be the same person . thanks Dave
  24. Hi, Daved. You're right, people do post links to that paper a lot. Fortunately, this site is here to help people quickly assess those kinds of claims. The short answer is that the "falsification" paper by G&T is just nonsense. You can find a rebuttal to it on this site at The greenhouse effect and the 2nd law of thermodynamics Or, if you want more depth, there's a lot of discussion of this at the website "Science of Doom": On Having a Laugh – by Gerlich and Tscheuschner (2009) On the Miseducation of the Uninformed by Gerlich and Tscheuschner (2009) and subsequent posts at Science of Doom.
  25. Thanks Ned After another hour of searching I found Science of Dooms response in another blog with a link to his ? blog .

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