In addition to hotter temperatures, sea level rise, and extreme weather events, climate change may also cause more violent behavior in humans, researchers from UC Berkeley report. The study, published Thursday in the peer-reviewed journal, Science, draws a link between increased rates of violent crimes and a warming climate.

Authors of the study found that incidences of conflict, including domestic violence and ethnic violence, increased with rising temperatures. The researchers looked at 27 studies of modern societies, which all showed a correlation between higher temperatures and increased rates of violence.

“The authors suggest that even a small increase in average temperatures or unusual weather can spark violent behavior. They found an increase in reports of domestic violence in India and Australia at times of drought; land invasions in Brazil linked to poor weather; and more controversially, a rise in the number of assaults and murders in the US and Tanzania,” The Guardian reports.

The study projects that war and civil unrest may increase by as much as 56 percent between now and 2050 as a result of warmer temperatures and extreme rainfall patterns. Episodes of murder, rape, assault, and domestic abuse could increase by 16 percent.

“Drawing from archaeology, criminology, economics, geography, history, political science, and psychology,” the three Berkeley researchers collected 60 existing studies containing 45 data sets and analyzed the data using a “common statistical framework.”

The study assumes a global temperature increase of 4 degrees Fahrenheit over the next fifty years, based on data from the World Climate Research Programme in Geneva. The researchers concluded, “We find strong causal evidence linking climactic events to human conflict across… all major regions of the world… Amplified rates of human conflict could represent a large and critical impact of anthropogenic climate change.”

It has long been understood that a changing climate could produce conflict due to human displacement resulting from flooding, drought, loss of habitable land, and extreme weather events. Severe weather can lead to water crises, food shortages, and vast infrastructure damage. And displacement can lead to religious conflict, political violence, and the spread of contagious disease.

In 2008, the National Intelligence Council concluded that “climate change by itself would have significant geopolitical impacts around the world and would contribute to a host of problems, including poverty, environmental degradation and the weakening of national governments.”

While the authors observed a link between conflict and temperature across every region of the world and every time period they examined, they can only speculate about the reasons behind the link. “The physiological mechanism linking temperature to aggression remains unknown,” they stated.

“We like to compare it to smoking,” researcher Marshall Burke told the Los Angeles Times. “In the 1930s scientists were figuring out there was this really strong relationship between smoking and lung cancer, but it wasn’t for many decades after that they figured out the precise mechanism that links smoking to lung cancer.”
