Why, exactly, does more CO2 in the atmosphere result in more trapped heat?
If CO2 were essentially transparent to infrared waves, I can see why more CO2 would trap more infrared--doubling any transparent gas would double the "dimming" effect of that gas.
But I thought the heat-trapping effect of CO2 came from its absorption spectrum. CO2 is NOT transparent to all wavelengths of infrared radiation. In those wavelengths, CO2 acts like paint, not air. Putting two coats of paint on a window doesn't block twice as much light as one coat of paint.
It's like water--light can't travel very far through water. There's NO visible light a half mile down. Going twice as deep doesn't make it any darker.
So my new question is: which wavelengths of CO2 are only PARTIALLY absorbed by atmospheric CO2?