It's a natural cycle.

It's all just a natural cycle of warming and cooling. Every few million years, a sentient species digs up all the accumulated carbon deposits, lights fire to them, and warms up the planet again, rebooting the cycle. Humans have nothing to do with it, it's destiny.

EDIT: And, as Spengler says about just this sort of thing, "It's not the end of the world, it's the end of you." Of course, addressing the problem is "the end of you" as well, if you think of the high-consumption American lifestyle as defining yourself.