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Discussion > CO2 theory question

OK. let's put it as simply as possible. Is there a mathematical/theoretical basis for assessing the likelihood of a IR photon from the surface running into a CO2 molecule in its journey through the atmosphere?

I am aware of the modtran/hitran data sets but I kinda assumed they were all empirical and designed to answer USAF/USN requirements for missile and IR detection purposes. Correct me if I have that wrong.

Bonus points for matching the theory and the measurements!

Aug 27, 2012 at 12:38 PM | Registered Commenterrhoda

Surely ALL CO2 molecules will be hit by IR photons/radiation in proportion to the CO2 ppm level?

This question by Dumbo Dung :P

Aug 27, 2012 at 1:15 PM | Registered CommenterDung

Are you sure ppmv is the right measure? Not partial pressure, which would at least give an equivalent to density where ppmv does not?

And if all CO2 molecule are hit, we still don't know how many photons get clean away.

Aug 27, 2012 at 1:37 PM | Registered Commenterrhoda

Photons "not at the wavelengths which CO2 will absorb" all get clean away, they pass through the CO2. OK I have been reading hehe:

Wavelengths of IR radiated by the Earth centre on about 14 micrometres, CO2 absorbs at about 11 mm. The distribution curve of Earth's emission wavelengths runs from about 17mm to 11mm so not much is being emitted at 11mm. CO2 absorbs all of it. Adding more CO2 has no effect.

Aug 27, 2012 at 2:21 PM | Registered CommenterDung

Yes Dung, but i'm trying to get there by a logical sequence. Although satellite measurements have recorded a change in absorption in the CO2 bands. One of the bands is (possibly) still changing, the other not. This is on the Harries et al paper which promised much but failed to deliver for whatever reason. Still no link between theory and measurement on the GHE is apparent. I wonder why.

Aug 27, 2012 at 2:42 PM | Registered Commenterrhoda

Rhoda

It is a tough question you have asked ^.^ For me "A Photon" is just like Schrodinger's cat, it is a convenient way of describing part of the electromagnetic radiation spectrum in order to make the maths easier.

At night I dont see how anything on the surface is likely to be radiating in the IR wavelengths and so CO2 becomes irrelevant. During the day sand, concrete etc will be radiating IR but vegetation will not. It does not seem to be something that can be in any way global.

For now I will continue to read and leave it to others better qualified to help you.

Aug 27, 2012 at 3:13 PM | Registered CommenterDung

Just one last comment; I am surprised that you mentioned Modtran and Hitran since they are both models and therefore based on assumptions that may or may not be correct.

Aug 27, 2012 at 3:38 PM | Registered CommenterDung

There is a fairly detailed description of Hitran at http://www.cfa.harvard.edu/hitran/Download/HITRAN96.pdf which you may find of interest.

Aug 27, 2012 at 5:02 PM | Registered CommenterJonathan Jones

I understood modtran and hitran to be based originally on measurements then translated to models. I see now there is no such claim in the current editions, so models it is. I see that there is an ongoing effort in the apectroscopic community to refine the models in the light of new measurement techniques. All to be commended, and I suppose we should accept them as mostly right most of the time.

I think everything will radiate IR at night until it reaches 2.75K or morning comes. You can it seems produce ice in the desert by radiative methods if the sky is clear.

Aug 27, 2012 at 5:03 PM | Registered Commenterrhoda

Once upon a time I admired Oxford housewives but I have been reading about particle physics and blackbody radiation all afternoon and now my head hurts >.<

Aug 27, 2012 at 8:50 PM | Registered CommenterDung