quote:The positive feedback that is mentioned time and time again baffles me. How can the total radiation falling on the Earth's surface be greater than the Solar radiation that enters the top of the atmosphere? Where does the energy for this process come from? Is this what the IPCC call Radiative Forcing?
Assume energy from the sun stays constant, Infrared radiated from the earth doesn't all leave before some is 'captured' by a greenhouse gas and then some of that is thrown back at the earth so adds to the energy from the sun. Increase the greenhouse gas and more gets thrown back so it gets warmer (that's forcing). That causes water to evaporate which is also a greenhouse gas and that captures more outgoing IR and throws some more back (That's positive feedback). ie less IR leaves the top of the atmosphere until the surface warms and radiates even more. So no extra energy from the sun but more is recycled before finally leaving.