Will global warming lead to more war, crime and violence?

Scientists say an analysis of 60 earlier studies offers strong evidence of a link between higher temperatures and human conflict in all regions of the world. Solomon Hsiang, Marshall Burke and Edward Miguel of the University of California at Berkeley report that research suggests higher temperatures, drought and extreme rainfall can increase the risk of both individual and societal violence. In a paper published in the journal Science, the authors write that for every standard deviation of temperature increase, personal violence such as assault, domestic abuse and rape can be expected to increae by four percent, and societal violence such as rioting and war, can be expected to rise by 14 percent. Global temperatures are expected to rise at least two standard deviations by 2050, according to a story by Ed Yong in The Scientist.com. 

Thomas Homer-Dixon, an environmental and political scientist at Waterloo University in Ontario, who was not involved in the study, told Yong the research is exceptionally strong and added that the world is likely to be a pretty violent place by mid-century if climate change continues unabated. "Our results shed new light on how the future climate will shape human societies," Burke said in a Berkeley news release. "The findings of the study suggest that a global temperature rise of two degrees Celsius could increase the rate of intergroup conflicts, such as civil wars, by over 50 percent in many parts of the world.

Hsiang's team looked at data gathered by 190 scholars in diverse fields that included psychologists examining the impact of temperature on aggression and archeologists looking at violence in ancient civilizations. Worldwide data stretched from 10,000 BCE to the present. A Fastcoexist story reports researchers from the University of Minnesota found the collapse of the Tang, Yuan and Ming Dynasties all followed long periods of drought or scant rainfall, and worldwide warming has been documented around the time the Tang Dynasty fell. U.S. crime statistics show more murders, assaults and rapes on hot days. Hsiang's earlier research shows civil conflicts in the tropics are twice as likely during hot El Nino years, and Brazilian farmers are more likely to invade each other's land during years that are extremely wet or dry.

Skeptics say climate and conflict are complex subjects, and the relationship between them is unclear and nonlinear. A Washington Post story by Brad Plumer asserts the 2000s were the warmest decade on record and also the least violent since the 1970s. The Post report has links to several stories about the new study. Economic and political conditions not always related to climate contribute to violence. When climate contributes to famine induced by crop failure, or the relocation of refugees fleeing natural disasters, proportionality of the causes may be hard to assign.

Hsiang told The Scientist that while climate and conflict were consistently linked in his team's research, climate is only one influence. Further, his team did not attempt to show reasons for the link. Humans will inevitably be impacted in some way by climate change and environmental upheaval. In Hsiang's view thinking about the future of climate change and its consequences can help people adapt.

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