My apologies for being away for a bit. I don't have enough time to read through all the recent postings, so I'll just respond to your response to my post.
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).
I fully understand the different absorption bands that H20 and C02 have. CO2's absorption bands are in the 2, 3, 5, and 13-17 micron ranges. I never said H2O absorbed IR within these ranges, just that is it responsible for, by far, the majority of IR absorption.
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).
You're saying there's enough IR radiation in the 4-5 range, that it would take a atmosphere made up of 85% CO2 before the IR was absorbed to extinction??? Reference please. I'd love to know where you got this from.
This is completely at odds with everything that I've read. Here's a link to a wikipedia page with showing the atmospheric transmission of IR.
http://en.wikipedia.org/wiki/Image:Atmospheric_Transmission.png
You'll notice that in
all of the CO2 absorption bands (2, 3, 5, and 13-17), the amount of IR leaving the earth is 0. The IR that is leaving the globe is within a fairly narrow band of ~8-13 microns. There's next to no IR leaving the earth's atmosphere other than within that range. Which, I'll remind you, is outside the absorption range of CO2.
That same page has the absorption that is responsible from each major GHG, and you can easily see 100% absorption already occurring in the each of the absorption bands for CO2.
The theory of AGW is that as the atmosphere becomes more "optically thick" with CO2, there is more CO2 available to reabsorb emitted IR from the CO2 molecules which originally absorbed the initial IR emitted from earth. This, in theory, warms the earth, as energy is held within the atmosphere longer before being lost to space.
The other thing (which I did have wrong), is the pressure broadening of the CO2 absorption bands due to increases in partial pressure (brought along by the increased concentration), not lowering pressures as I stated. My apologies.....this idea that absorption characteristics can change depending on the concentration of molecules seem a little odd to me. I need to do some more reading on this.
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.
I believe we are talking about different portions of the atmosphere. As you mention, the stratosphere is supposed to cool, this is because as the atmosphere becomes "optically thicker", heat takes longer to reach the atmosphere. This reduces the heat flow to the stratosphere (until the atmosphere reaches steady state), and because the stratosphere continues to radiate heat to space at the same rate as before, it cools down.
The upper troposphere (which is much lower than the stratosphere), is supposed to warm. And at a greater rate than the near surface.
This page has good info on the cooling/warming characteristics of the various portions of the atmosphere.
http://www.remss.com/msu/msu_browse.htmlThis seems (to me) to be a good page on describing the IR adsorption physics behind AGW - and a quote for you samewise
It is generally accepted that the concentration of carbon dioxide in the atmosphere is already high enough to absorb almost all the infrared radiation in the main carbon dioxide absorption bands over a distance of only a few km
