And it's not just about mass extinction; humanity itself is already a mass extinction event. But it will also be harder to feed people if the climate becomes unpredictable. Inhabited places can become less habitable. And the big one: if the eastern Antarctic ice cap starts melting, we're eventually going to have to evacuate most major population centers.
That is indeed not something we'll be able to handle. And we have frankly no idea when the exact deadline is that we may be able to prevent that from happening, or whether we may already have passed it, but we do know that many other ice caps are already melting, which is bad enough in itself, but also a warning for what might still come.