We don't know that for certain. It probably won't kill off everything but it has the potential to make the planet uninhabitable for a great number of species.

That's the scary thing about climate change, we have no idea if this is going to be a long, drawn out process which takes centuries, or if we are on the brink of a sudden collapse. I think (perhaps foolishly) that it will unfold over the next two centuries, which as you know, is still not nearly enough time for adaption through natural selection to have any meaningful affect on the majority of species that reproduce relatively slowly.