I'm working on a book set partially near the collapse of the Mayan civilizations on the Yucatan peninsula. In my research, I've come across numerous references to climate change as a probable cause for the quick decline of rich, vibrant civilizations. Yes, there are others, including a significant asteroid strike (which could have also contributed to climate change).
Like we are now, that civilization was one of the historically ascendant and stable populations of its time, with a rich economy and ready access to resources.

The climate change in that time (a shift to a dryer climate) appears to have been largely local. The one we are in the midst of now is not. It is global. We should take the history lesson to heart.

I'd also like to link to Glen Hiemstra's excellent blog post about the meaning of the Gore appointment to help England deal with it's global warming actions.