Claims that global warming can drive civil unrest are hotly disputed. In his popular 2008 book Climate Wars, the US journalist and military historian Gwynne Dyer laid out a daunting scenario. Climate change would put growing pressure on fresh water and food over the coming century, he wrote, triggering social disorder, mass migration and violent conflict. But is there real proof of a link between climate change and civil war — particularly in crisis-ridden parts of Africa — as many have claimed? No, says Halvard Buhaug, a political scientist with the Peace Research Institute Oslo in Norway. In research published...