Is the CO2 effect 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." (Source: Marc Morano)

Comments 1 to 11:

1. GFW at 11:02 AM on 16 October, 2009
   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. GFW at 11:06 AM on 16 October, 2009
   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. rlasker3 at 03:26 AM on 17 October, 2009
   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. PeterPan at 08:21 AM on 20 October, 2009
   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. HumanityRules at 18:15 PM on 26 October, 2009
   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. aku at 22:41 PM on 24 November, 2009
   i thought venus's atmospheric pressure has a lot to do with its temperature?
7. NkThrasher at 17:41 PM on 7 December, 2009
   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. Tom Dayton at 18:05 PM on 7 December, 2009
   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. mazibuko at 05:19 AM on 8 March, 2010
   What do you make of this claim?
   
   http://jimpeden.blogspot.com/2009/11/norm-kalmanovich-on-global-warming-hoax.html
   
   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. Riccardo at 05:53 AM on 8 March, 2010
    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. mazibuko at 15:16 PM on 8 March, 2010
    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

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