About those humans heating the Earth -- the effect of the GHG's we emit is tapping into solar insolation, which is huge, so it probably dwarfs the above figures (see next paragraph). Also, the energy that powers us (food) would be turned into heat by other processes anyway.
Order of magnitude: population of 7 billion * 100W/person = 9.7TW. Solar insolation 1361 W/m^2, over the projected area of the earth, which totals 175,000,000 TW.
I just throw that figure (100W) as a useful order of magnitude estimate.