Yes, your first paragraph is completely true. H2O is stronger (there's more of it and it absorbs over a wider range of wavelengths), but it does not absorb where CO2 absorbs (between 4-5 microns); hence the "strength" of the two is unrelated in terms of IR absorbance (apples and oranges logic).
But what the heck is your second paragraph talking about?
Extinction? At atmospheric pressure ranges? Where did you get this from?
The blackbody radiation from Earth (at 4-5 microns) far outstrips the capacity for CO2 to absorb it all (until our atmosphere gets up to >85% CO2).
It is theorized that at lower pressures (higher elevations), the absorption band for CO2 will broaden, which will allow more IR to be absorbed....
What new physics is this? They've already tested gasses at different pressures. Absorbance spectra don't broaden or narrow until you start changing phase to a liquid or solid. Where did you get this info. from?
I think it's emission spectra that change with pressure.
Standard physics tells us that at lower pressures, CO2 can radiate heat away (to space) more easily, as at these lower pressures, there are fewer collisions to translate (retaining) the heat, and there is less chance of another molecule re-absorbing any released IR. Maybe we're talking about different layers of the atmosphere here, but the "physics" that I know predicts higher concentrations of CO2 will increase cooling in the upper levels (lower pressure levels) of the atmosphere.
Maybe we're both wrong (it's been 30 years since I took classes in this stuff), or maybe we're both right and just not expressing it very well; but I'd like to find out whether you know this physics yourself or if you've learned this stuff second hand (and where can I learn more of it)?
