A simple word experiment proves radiative effects of CO2
Posted by Jeff Id on August 5, 2010
Tom Vonk wrote an interesting post at WUWT in which he describes some of the quantum mechanics of IR absorption and makes the conclusion that radiative energy delay effects of CO2 are flatly false. Click the headline for Tom’s excellent article.
Guest post By Tom Vonk (Tom is a physicist and long time poster at many climate blogs. Note also I’ll have another essay coming soon supporting the role of CO2 – Anthony)
The simplistic view of CO2 heat trapping
If you search for “greenhouse effect” in Google and get 1 cent for statements like…
“CO2 absorbs the outgoing infrared energy and warms the atmosphere” – or – “CO2 traps part of the infrared radiation between ground and the upper part of the atmosphere”
…you will be millionaire .
Even Internet sites that are said to have a good scientific level like “Science of doom” publish statements similar to those quoted above . These statements are all wrong yet happen so often that I submitted this guest post to Anthony to clear this issue once for all.
Of course the Air Vent is one of those sites he claims is wrong, I left a comment explaining where he went wrong in his analysis, it seems to have vanished from the moderation queue it’s up now.
Tom really did do a good job, so I’m not disparaging his work, what it does do though is create a lot of confusion in the crowd which is something Tamino accuses every non-extremist warmer of doing. Here is an experiment he defined as proof that the energy in equals energy out so that CO2 simply cannot cause warming.
For those who prefer experimental proofs to theoretical arguments , here is a simple experiment demonstrating the above statements . Let us consider a hollow sphere at 15°C filled with air . You install an IR detector on the surface of the cavity . This is equivalent to the atmosphere during the night . The cavity will emit IR according to a black body law . Some frequencies of this BB radiation will be absorbed by the vibration modes of the CO2 molecules present in the air . What you will observe is :
- The detector shows that the cavity absorbs the same power on 15µ as it emits
- The temperature of the air stays at 15°C and more specifically the N2 and O2 do not heat
These observations demonstrate as expected that CO2 emits the same power as it absorbs and that there is no net energy transfer between the vibrational modes of CO2 and the translational modes of N2 and O2 . If you double the CO2 concentration or make the temperature vary , the observations stay identical showing that the conclusions we made are independent of temperatures and CO2 concentrations .
It’s a simple concept the gas in a sphere filled with CO2 has the same temperature as a sphere filled with N2. It’s also correct. However, it is moot with respect to AGW. The basis of his claims is essentially that energy in = energy out. Which it does, if you take the time to read his post though, he uses correct physics to come to an incorrect conclusion. Deciding that radiative effects of CO2 aren’t real and AGW cannot exist. My comment at WUWT, rewritten for clarity, is below.
If define an experiment this way:
A thin rectangular box having two very large sides A and B parallel and opposite to each other, the other 4 sides having negligible area. Side A is a 1000Watt 15um IR emitter, side B is a perfect IR absorber.
If we take N2 and fill the volume, the N2 will reach an equilibrium temperature based on the temperature of the box and whatever radiation is absorbed. Now if we instantly change the gas content to be 50/50 N2 and CO2 which has better absorption of the 15um IR wavelength, an IR detector at side B would detect an instantaneous drop in IR energy at the 15um wavelength. I’m sure we can agree on that.
Co2 is basically black stuff at 15um, so when it is first introduced, side B would receive less than the equilibrium 1000 watts.
What would then happen over time, is the gas inside the box would stabilize to an equilibrium temperature representing the temperature of the box and the radiation absorbed. As the system stabilized, an energy detector at the absorbing B side would eventually record the same 1000Watts of energy transfer from the A side as before.
However, the gas temperature will stabilize slightly higher than the N2 gas. An effect guaranteed and in fact proven by the initial drop in IR at your detector and the time delay until the system re-stabilizes.
None of this violates your equations or assumptions.
Good try though.
I say both experiments are right, but Tom’s conclusions are wrong. So I wonder who can describe what the difference is between my experiment and Tom’s?