If any one you watch PBS (which I love), there was just a documentary about the impacts of global/environmental change on sociological and political conditions historically.

If I can find the link I will post it here.

Basically it shows the link between climate change, food shortages, human migration to deal with the food shortages and the ensuring strife caused by over crowding with minimal food supplies.

The documentary even explains, with concrete evidence, why the Roman Empire fell, the Inca civilization fell, and why the great plagues hit Rome and the U.K.

There is evidence of that exact thing happening now, including the loss of an entire large village in India because of rat infestation (they are looking for food).

History repeats itself....

Oh, and by the way, the start of the climate change was associated with a change in atmospheric conditions and the subsequent impacts on the icecaps.