Passenger pigeons did not have the capacity to alter their environment.

I simply find it unlikely that any amount of climate change (beyond the eventual death of our sun) will result in the complete elimination of humanity.

Yes, there are many likely bad scenarios that would drastically reduce the population.

The easy scenario to imagine where humans become extinct due to climate change is the scarcity of resources that will lead to the drastically reduced population will cause full on nuclear war to secure those scarce resources. Given our history I actually find it quite plausible. "If I can't have it nobody will."

Extinction is commonplace. I think it's pretty outlandish to assume, after having only been on the scene for a million years or so, that we're going to make it to a billion.

If survival is so easy, why isn't the sky teaming with alien radio chatter?