[moose07]

CO2 captures outgoing IR photons (a well studied fact). In fact, there is enough CO2 even at 0.04% to trap all outgoing IR photons within 100 meters (IIRC). Then those photons almost instantly give up that energy to the surrounding N2 and O2. Thus the atmosphere is warmer with CO2 than without.

Interesting bit of info.
So doubling the Atmospheric Co2 levels would have no effect on the thermal capturing that takes place as the IR adsorbsion rate is already 100% ?

[palmer]

The trick is to think about the atmosphere as layers. Even when a layer is saturated the next layer above will still warm because it receives outgoing IR from the layer below.

[palmer]

But, it is the reason why there are decreasing returns on added CO2. There is a logarithmic decrease in the warming with a linear rise in CO2. Since CO2 is going up relatively linearly, the amount of warming will steadily decrease.