John,

Oh, I think I see your logic; there's no net change after the IR is re-emitted, therefore no heating? Where do you think it goes?

I wrote this below, after first reading your post. After re-reading, the below still applies, and explains the heating of the atmosphere, even if the CO2 has no net change (really it's in an equilibrium, between having absorbed some IR and having re-emitted some IR; there's no final, net, state).

So, initially, in response to your post....
Even if IR did not contribute to "kinetic energy" (via collisions you mean?), the re-emitted radiation does get absorbed by other air molecules frequently enough to "contribute to a rise in air temperature." But CO2, energized by IR absorbance, can also translate that extra heat to other air molecules, via collisions.

Perhaps, when you say, "does not contribute to the kinetic energy of the molecule," you are referring to the rotational and stretching vibrational modes for CO2. These could be considered as "potential energy;" but in the long run, that energy is either re-emitted as IR, or lost through collisions (kinetically, just as with any gas molecule).

Originally Posted By: JMR
The small frequency band that CO2 absorbs combined with the small 0.0387% of the atmosphere that CO2 takes up, leaves little radiation for the CO2 molecules to reflect back to earth.
...or 'leaves little radiation for the CO2 molecules to absorb and then reflect back to earth (or other molecules).'

Anyway, yes; that a fair qualitative assessment.
Quantitatively however, one needs to realize that losing all the water vapor in the atmosphere would change things by 70-100 degrees (cooler); whereas losing all the CO2 in the atmosphere would only drop the temperature by about 5-10 degrees. Conversely, doubling or tripling the CO2 would only add 5-10 degrees.

Just to be clear, when you say "leaves little radiation," it's important to realize that there is lots of heat at 4-5 microns, as well as more at the shorter wavelengths. There's no danger of "running out of 4-5 micron radiation" for CO2 to absorb or "reflect."

As to the link.... Hey!
This link has nothing to do with what we're talking about here.

It doesn't even mention, much less test, CO2!
It only deals with the greenhouse effect of glass. The substances, glass and CO2 (& as noted, along with rock-salt) all behave differently in response to solar radiation.
...and, as the original poster noted, the conclusions are wrong.
~SA

Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.