Guest post By Ben Herman and Roger A. Pielke Sr.
During the past several months there have been various, unpublished studies circulating around the blogosphere and elsewhere claiming that the “greenhouse effect” cannot warm the Earth’s atmosphere. We would like to briefly explain the arguments that have been put forth and why they are incorrect. Two of the primary arguments that have been used are
- By virtue of the second law of Thermodynamics, heat cannot be transferred from a colder to a warmer body, and
- Since solar energy is the basic source of all energy on Earth, if we do not change the amount of solar energy absorbed, we cannot change the effective radiating temperature of the Earth.
Both of the above statements are certainly true, but as we will show, the so-called “greenhouse theory” does not violate either of these two statements. (we use quotation marks around the words “greenhouse theory” to indicate that while this terminology has been generally adopted to explain the predicted warming with the addition of absorbing gases into the atmosphere, the actual process is quite a bit different from how a greenhouse heats).
With regards to the violation of the second law, what actually happens when absorbing gases are added to the atmosphere is that the cooling is slowed down. Equilibrium with the incoming absorbed sunlight is maintained by the emission of infrared radiation to space. When absorbing gases are added to the atmosphere, more of emitted radiation from the ground is absorbed by the atmosphere. This results in increased downward radiation toward the surface, so that the rate of escape of IR radiation to space is decreased, i.e., the rate of infrared cooling is decreased. This results in warming of the lower atmosphere and thus the second law is not violated. Thus, the warming is a result of decreased cooling rates.
Going to the second statement above, it is true that in equilibrium, if the amount of solar energy absorbed is not changed, then the amount of IR energy escaping out of the top of the atmosphere also cannot change. Therefore the effective radiating temperature of the atmosphere cannot change. But, the effective radiating temperature of the atmosphere is different from the vertical profile of temperature in the atmosphere. The effective radiating temperature is that T that will give the proper value of upward IR radiation at the top of the atmosphere such that it equals the solar radiation absorbed by the Earth-atmosphere system.
In other words, it is the temperature such that 4 pi x Sigma T4 equals pi Re2 Fso, where Re is the Earth’s radius, and Fso is the solar constant. Now, when we add more CO2, the absorption per unit distance increases, and this warms the atmosphere. But the increased absorption also means that less radiation from lower, warmer levels of the atmosphere can escape to space. Thus, more of the escaping IR radiation originates from higher, cooler levels of the atmosphere. Thus, the same effective radiating temperature can exist, but the atmospheric column has warmed.
These arguments, of course, do not take into account feedbacks which will kick in as soon as a warming (or cooling) begins.
The bottom line here is that when you add IR absorbing gases to the atmosphere, you slow down the loss of energy from the ground and the ground must warm up. The rest of the processes, including convection, conduction, feedbacks, etc. are too complicated to discuss here and are not completely understood anyway. But the radiational forcing due to the addition of greenhouse gases must result in a warming contribution to the atmosphere. By itself, this will not result in a change of the effective radiation temperature of the atmosphere, but it will result in changes in the vertical profile of temperature.
The so-called “greenhouse effect” is real. The question is how much will this effect be, and this is not a simple question. There are also questions being raised as to the very sign of some of the larger feedbacks to add to the confusion. Our purpose here was to merely point out that the addition of absorbing gases into the atmosphere must result in warming, contrary to some research currently circulating that says to the contrary.
For those that might still question this conclusion, consider taking away the atmosphere from the Earth, but change nothing else, i.e., keep the solar albedo the same (the lack of clouds would of course change this), and calculate the equilibrium temperature of the Earth’s surface. If you’ve done your arithmetic correctly, you should have come up with something like 255 K. But with the atmosphere, it is about 288 K, 33 degrees warmer. This is the greenhouse effect of the atmosphere.
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Since this thread is now old, I will keep it short.
David Springer, the CO2 effect is not negligible away from the poles. I see cba ran the numbers since the last post. However, the biggest effects are higher in the atmosphere as you get to the tropics, where the air is drier. 4 W/m2 translates to a degree warming in the equilibrium if it is sustained at the ground.
I am not sure I understood your 11:15 question, but we don’t expect to see any “reflected” IR. It doesn’t reflect or scatter in the clear atmosphere (remember shorter wavelengths scatter more).
Joel Shore says:
July 29, 2010 at 1:36 pm
I agree the thread is now moribund, but cannot let this slip by.
Well, Joel, in the sense of the “Projections” being, like oracles, black boxes, with input parameters and output plots, I would agree that the IPCC AR4 projections are falsifiable, and in my oponion, they are falsified already as I listed seven contradictions in
http://wattsupwiththat.com/2010/07/25/seven-eminent-physicists-that-are-skeptical-of-agw/#comment-439290 .
The fact that the venerable societies have swallowed whole the report and have not looked at the falsification from the data, speaks about the level of veneration one should have for such authorities, which have become politicized and follow the leader mouthpieces.
In the philosophy of science sense though, looking at the axiomatic foundations thereof, Terry Oldberg is right. When gross contradictions arise it means that logical falsifiability has been lost and also the claim to a consistent scientific proposition .
Not quite true, Jim. There is no such thing as a perfect absorber or perfect reflector. Some reflection and scattering occurs at all frequencies. This is why an interferometer is required to dig the 15 micron downwelling CO2 signature out of what would be, to any other less sensitive instrument, a continuous blackbody spectrum.
As to CO2 being significant – it’s swamped by H2O at and near the surface virtually everywhere in the world. By the time you get high enough in the atmosphere where there is little vapor left there is little CO2 left either. For one thing CO2 is heavier than air and requires air movement to mix it upward. Secondly the atmosphere is more tenuous higher up and has less impact. Thirdly, cold dense gases that absorb in spectral lines emit predominantly in continuous black body spectra as collisions occur far more often than re-emission. Even at higher atmospheric altitudes the air is still “dense” when it comes to collisions although it certainly becomes easier and easier to dig charateristic emission lines out of the continuous blackbody spectrum as altitude increases.
“virtually all” is a logical fallacy known as ad populum
“reputable” is a logical fallacy known as ad hominem as it implies organizations in disagreement are disreputable
“scientific organizations” is a logical fallacy known as “appeal to authority”
Pretty good performance there Joel. You managed to squeeze three logical fallacies into five words.
@jimd (con’t)
“I see cba ran the numbers since the last post.”
Yes, he did. And the most relevant result is that CO2 doubling only increases it’s effectiveness as an insulating GHG by 10%.
I’ve covered that little factoid many times. In fact the first 100ppm CO2 does almost all the significant insulating. More than that simply raises the optical depth at which CO2 is absorbing nearly all available energy in its absorption bands. The optical depth difference is a matter of tens to hundreds of meters which is to essentially a nil difference for circulation models.
For the lay person to understand it’s like adding blankets to keep warm at night. The first blanket does most of the job because the difference between butt naked in the cold and having one blanket is stark. Adding an additional blanket helps but they each have less and less effect at keeping you warm – adding a fifth blanket isn’t going to do much more than four blankets underneath.
I’ve never meant to say CO2 has no effect. I should maintain a constant vigil to say that anthropogenic CO2 (280ppm to 380ppm) has no significant effect on climate.
And it’s damn good thing we have over 200ppm because plant growth virtually stops much below that point. At the same time plant growth continues to improve up through at least 1000ppm and it uses less water per unit of growth as CO2 rises which adds even more to its benefit as adequate water can be a limiting factor in both nature and agriculture, especially in agriculture if you want to focus on what feeds the human population vs. whatever eats sagebrush and tumbleweeds.
So Jim, what exactly is the negative aspect of anthropenic CO2 that so overwhelms the positive aspect? What exactly is it that should worry me so?
If you say anthropogenic CO2 is a proxy for fossil fuel consumption and that I should worry that peak oil is bridge we’ve already crossed then I’ll say that is a legimate worry.
But here’s the thing about that. Developing suitable replacement sources of energy against the day when economically recoverable fossil fuels run out will be hampered by the trillions of dollars effort to slow down fossil fuel use that will only marginally delay the inevitable.
If we’ve got that kind of money to burn (pun intended) we should put it into things like better and cheaper photovoltaics, advanced nuclear reactors with fuel cycles that don’t yield weapons grade fissile byproducts, genetic engineering (a personal favorite) to get a simple clean biological sequence converting sunlight, air, and water into alcohol or fuel oils, and things of that nature.
If anything should be done about atmospheric CO2 concentration it should be to have a plan to keep the concentration high for its great benefit to plant life (and hence everything higher up in the food chain) after we don’t have enough fossil fuel left to keep it artificially inflated. Anthopogenic CO2 is a good thing.
That’s the sane thing to do, Jim. What the CAGW cabal proposes will put enormous economic resources into something that does far more harm than good.
Dave Springer says:
July 30, 2010 at 9:42 am
@jimd (con’t)
“I see cba ran the numbers since the last post.”
Yes, he did. And the most relevant result is that CO2 doubling only increases it’s effectiveness as an insulating GHG by 10%.
I’ve covered that little factoid many times. In fact the first 100ppm CO2 does almost all the significant insulating. More than that simply raises the optical depth at which CO2 is absorbing nearly all available energy in its absorption bands. The optical depth difference is a matter of tens to hundreds of meters which is to essentially a nil difference for circulation models…..
A very nice final summation, thank you.
I wish instead of all the hype and politics they just would allow the building of nuclear power plants. I look out the window and see one and I prefer that to a bunch of bird eating wind mills.
Found a mistake in my first posting: It should be 1942, not 1948.
July 28, 2010 at 9:16 am
Dr. Elsasser’s classic, “Infrared Heat Transfer in the Atmosphere” is available at ScribeD.
http://www.scribd.com/doc/34962513/Elsasser1942
Page 23 is rather interesting!
Please note someone screwed up in the PDF, the first 2 or 3 pages are from the end of the paper, i.e. bibliography.
And page 23 of the paper appears on page 25 of the ScribeD.
Aside from that, I’d say the comment on CO2 Upflux and Downflux should “flux up” some people.
Happy downloads.