What we should do is transition away from fossil fuels as quickly as is reasonably possible. Not simply pull them all at once, because that won't help anything as you say, but start moving smartly in that direction. Fortunately we already are, even if not as quickly as we'd like. I think in the next few years we'll see rapid change as solar panels and batteries become cheap enough to compete with traditional energy on their own terms.

I don't see the case for human extinction here. Your link mentions it, but doesn't appear to lay out the case at all, so I don't know what that statement is based on, but I don't see how it would occur. The potential disruption due to climate change is immense, but people will survive. The problem is not how to keep humanity alive, but how to keep civilization going without some sort of major backslide, and without getting a couple of billion people killed.