There's no way climate change can wipe out the entirety of humanity and make the earth uninhabitable, especially in the next 15 years. Are greenhouse gases supposed to turn Earth into Venus in 15 years? That's the only way I see that it can truly become "uninhabitable", and I don't see how that can happen.

Even then, a small percentage can always survive in closed-loop habitats shielded from the outside world, ala Biosphere 2.0.