Ben Herman and I have already discussed the greenhouse effect on this weblog (i.e. see and see). In response to comments on other weblogs regarding our contributions there remain continued misconceptions on the greenhouse effect. To further emphasize the physics, we have written this new text.
Our discussions are based on the effect of adding absorbing (greenhouse) gases to the atmosphere. Of course there are many other things going on as the comments on the weblogs have stated. These will add or subtract from the warming effect due to greenhouse gases. This does not mean that greenhouse gases do not have a warming effect (by virtue of reduced cooling). That effect is still there. It is that effect and that effect alone that we were discussing, and the presence of all of the other factors that influence atmospheric temperatures will not eliminate that effect. They will only modify the final outcome.
One other point also seems to have been misunderstood by some. Infrared radiation (IR) will, in general, cool the surface of the earth. So how can addition of greenhouse gases which are primarily active only in the IR cause a warming of the surface?
As we pointed out originally, it is the absorbed solar energy that causes the warming. This absorbed energy, in equilibrium, is balanced by an equal emission of IR energy. When more of the emitted IR from the surface is absorbed by the addition of greenhouse gases in the atmosphere, and some of this additionally absorbed IR is re-emitted downward towards the ground, the ground cools more slowly, and thus is warmer than it was before the addition of the greenhouse gas.
Thus the final result is that the addition of an IR absorbing gas in to the atmosphere, results in a warming of the surface, and subsequently the lower levels of the atmosphere. The important remaining question, of course, is how much is this warming effect and in our opinion, this has not yet been satisfactorily answered.