I read a study a few years ago, I can't seem to find it again sadly, but the synopsis is: When the atmospheric heat increases, the trees and plants "sweat" and release more moisture which cools the atmosphere.

The other contention I have with the theory of AGW, is the fact that nobody, not 1 person, can definitively state how many undersea thermal vents and volcanoes are active and contributing to either warming oceans, OR heat release in general, since convection would end up warming our atmosphere to some degree if I understand the principle correctly.