"Climate change will take on a life of it's own and spiral out of control. Something like half the earth's currently-inhabited land would become too hot to survive on. I don't mean it's difficult to grow beans, or your air-conditioning bills are inconveniently high. I mean, if you go outside you die of hotness. Places that were an average of 80F will now be an average of 170, 180F. Will there still be human civilization under those circumstances?"
Wording and links lifted verbatim from this MeFi post.... it was so well done that I couldn't see any way to improve on it. The first link is a 15-minute TED talk that I found very engaging, and I don't tend to like video presentations as much as text. The latter two are text.