Science http://doi.org/ncd (2013)

There is increasing recognition that changes in climate lead to violence and social unrest, but available evidence is scattered across disciplines. Consistency among different studies would inform governments about the strength of the climate–conflict relationship.

Solomon M. Hsiang of Princeton University, USA, and colleagues developed the first comprehensive synthesis of existing research — from archaeology, criminology, economics, geography, history, political science and psychology — to examine whether human conflicts are affected by climatic changes. Sixty comparable studies were analysed, covering 45 different conflict data sets and representing the work of over 190 experts from around the world. They found strong evidence linking climatic events to human conflict across the world, throughout history and at all scales of social organization. For each one standard deviation change in climate towards warmer temperatures or more extreme rainfall than the average, the median estimates show that the frequency of interpersonal violence rises by 4% and that of intergroup conflict by 14%.

Expected warming by 2050 is thus likely to increase the rate of human conflicts.