The usual definition given for a greenhouse gas is that it absorbs infrared radiation. Of course, then the gas emits its own thermal radiation, and it does so without preference for direction ...
I'm trying to understand this "toy model" of the greenhouse effect. http://www.realclimate.org/index.php/archives/2007/04/learning-from-a-simple-model The model predicts the surface temperature of ...
A post (below) on the Bishop Hill blog relating to climate change asserts that no warming effect can be attributed to CO2. I don't know whether the author is really a physicist but it sounds ...