Well, in spite of the fact that I like Chris and respect his intellect, I have a far different take on the matter. Oh, not the history of this issue because that is well established ( [history.aip.org] ), but the outlook for the future. After all, when it comes to looking ahead more than 2 or three minutes, it is all conjecture anyway --- and we are dealing with human beings and how they behave under stress.

Because of the dynamics involved, there is a smooth spectrum of possibilities stretching from horizon to horizon wherein one may pick whatever "end result" that happens to fit their personality or agenda. The 3 he has chosen certainly are possibilities, but they are not eventualities and they are not fixed points.

It is likely we will have some difficult decades ahead because much of what has led us to this point is difficult to change and once changed will take as much as a century to have the desired effect. But take heart, there are many places on the globe where the changes are already beginning --- some of them have progressed quite a bit. Like the proverbial snowball, it will gain mass as it continues down the hill until it is unstoppable. I don't see our species winking out of existence, but it is entirely possible that there will come a great dying. That will be sad on one hand, but a boon for Earth and the remaining people on the other.

All is not lost. We are destined to find our way among the stars.

Some observations presented here are supremely negative:

And here is why there is more than ample reason for a positive outlook.