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CO2 Absorption
15u CO2 line absorption
- Highly saturated
- Energy limited, not concentration limited
- Double CO2
- Insignificant increase in width
- Primarily decreases mean distance before absorption
Other bands are between 2u and 4.3u
- Narrower lines
- Significant H2O overlap
- Far less energy available to be absorbed
Notes:
Relative to radiated surface energy, the most significant CO2 absorption line is at 15μ. This line is saturated, meaning that any photon whose wavelength is near 15μ has virtually a 100% probability of being captured by a CO2 molecule. Most are absorbed within the first few 100 meters from the surface. The largest effect increasing CO2 concentrations has, is to move this distance closer to the surface.
The other CO2 lines are in a region of the spectrum where there's little solar energy and little surface energy. Except for one relatively weak line, these are also saturated.
It's important to recognize that CO2 doesn't actually retain energy and acts only to transfer captured energy to the other molecules in the atmosphere through collisions. The bottom line is that the greenhouse effect of CO2, even at concentrations well below current levels, is energy limited and not concentration limited.