(2) CO2 Can't Heat the Atmosphere, But It Does Cool the Stratosphere

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Continued from here.

Writes CO2IsLife,

[...] Energy is transferred through the atmosphere by three mechanisms; Conduction, Convection and Radiation. Conduction and convection dominate the warm water vapor rich and dense lower atmosphere. Radiation dominates the upper atmosphere. 

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[...] Because the lower atmosphere is tightly packed, kinetic energy is easily passed from one molecule to the other. The radiative path is also very short relative to other altitudes, meaning that the molecules can momentarily “trap” more radiation resulting in warming. That is why high levels of water vapor in the lower atmosphere is so important. Water vapor traps and converts huge amounts of outgoing longwave radiation into thermal kinetic energy. 

[...] At higher altitudes, the molecules have wide separations representing large windows for radiation to easily pass. That is why CO2 works to cool the stratosphere. A molecule in the stratosphere radiating towards earth is radiating into a traffic jam, with an increasing number of radiation absorbing molecules in its path the closer it gets to earth. It is unlikely that the radiation from a stratospheric molecule will be able to pass the gauntlet of ever-increasing molecules and smaller and smaller windows to get to earth. On the other hand, a stratospheric molecule radiating towards outer space is facing the opposite of a traffic jam, with the spacing between cars increasing the farther away it gets, and the windows keep getting bigger and bigger. That is why radiation is best for cooling, not warming. It most efficiently transfers heat out of the atmosphere and it does it near the speed of light.