I just finished watching a fascinating video of a presentation by Brian Fagan at PopTech in 2004.  The video may be dated - but Brian's thinking is definitely not.

He's an archeologist and has been studying the impact of climate change on humanity - but from a very long term historical perspective.  He talks about how there have been times of massive climate change in the past and humans have had to make choices on how to adapt.

The first recorded one was about 8,000 years ago when Lake Agassiz began draining into the Atlantic.  Apparently so much water entered the Atlantic that it slowed and cooled the Gulf Stream - meaning that Europe almost went back to an ice age.

However, since Europe at the time consisted primarily of nomadic communities, they simply relocated and survived.

This contrasts with other societies that failed as they couldn't move when climate change occurred (sound familiar?): ancient Egypt (almost collapsed), numerous cities in Babylon and parts of ancient Peru.  One of the exact opposite societies was the Anasazi - after two centuries they abandoned their entire cities to move when a long-term drought occurred.

Incidentally, it's likely climate change that led to agriculture.  Apparently the cradle of modern civilization (Syria, Iraq, etc.) was originally a relatively lush area, until climate change (possibly because of the draining of Lake Agassiz; it took 1,000 years to empty) made the area less hospitable.  To counter the growing desert, the early occupants began planting grasses - which over the next few centuries led to widespread fields of wheat and eventual cultivation (how's that for a long-term unintended consequence of climate change?).