I don't think it's an exaggeration at all to say that global warming is the most serious problem that civilized humans have ever faced (Al Gore's movie is more optimisitic than the data justify), but I'm not worried about the Earth at all. Living systems will reach a new equilibrium in a few ten thousands of years at most, and then things will happily continue as before, only with far fewer humans, perhaps none. The interim, however, will probably really suck. Enjoy electrical lights and plentiful food while you still can.
The really sad thing is that, given enough political and cultural will, we might actually still be able to save ourselves; the rats and cockroaches will be just fine no matter what we do.