I'm not an ecologist, but my guess would be that most of the top of the food pyramid comes tumbling off if we continue as we do, and a lot of ecosystems will go into disequilibrium, causing further extinctions. It's a very dangerous situation for the human species to be in. We're not technologically ready to survive as more than a rump if the ecosystem services we rely on fall down. The amount of social upheaval that will accompany this transition makes planning it impossible. I'm pessimistic about human survival in the face of catastrophic climate change.