When humans are long gone, there will still be 80% nitrogen in the atmosphere and around 20% oxygen and around 1% other gases.

Bottomline is by messing up the planet humans are only hurting themselves and other species. Something else will come back, **** roaches, giant sponges or something, and repopulate the planet, unless somehow we manage to wipe out all life on earth.

Anyways, it's not really anything to worry about. Unless humans decide to start some real reform in population control and fixing the environment, global warming is kindof a non-issue compared to everything else.