Have you been paying attention at all to European or American politics? Even the very small amount of migration being driven by the Syrian civil war has caused massive amounts of discontent and unrest in the richest nations on Earth. Now imagine whole regions full of people wanting to move because rainfall patterns change, or sea level rise displaces them.

Social unrest is the biggest risk that climate change creates. People like things the way they are, and get very upset when they think things are going to change.

http://journals.ametsoc.org/doi/abs/10.1175/WCAS-D-13-00059....