Researchers from University of California, Berkeley analyzed 60 studies on climate change, ultimately concluding that by 2050, human conflict could rise by 50 percent due to the growing temperatures. The study covered all major types of violence and revealed large and clear changes in human behavior in response to climate.

"It does change how we think about the value of avoiding climate change," said the study's lead author Solomon Hsiang. "It makes us think that avoiding climate change is actually something we should be willing to invest more in."

Hsiang and his colleagues looked at human behavior in relation to climate over the past 12,000 years in order to find a link between hot weather and aggression, which they did. Intergroup conflict rose 14 percent and interpersonal violence rose four percent for each temperature rise. The meta-analysis was published in the journal of Science, with 78 percent of the relevant data coming from 2009 and after.

According to the United States Environmental Protection Agency (EPA), over the past century, the Earth's average temperature has risen by 1.4°F. Although this seems minute at first glance, small average temperature changes translate to large and potentially dangerous shifts in climate, which researchers have now revealed also creates hostile environments.

Human activities, such as releasing large amounts of carbon dioxide and other greenhouse gases out into the atmosphere by burning fossil fuels for energy, play an important role in climate change. These gases trap heat energy in the atmosphere and cause it to warm, ultimately increasing the overall average temperature of the earth.

The researchers wanted to make sure that their findings were as accurate and thorough as possible, and in order to do this, they examined studies from a wide variety of fields including climatology, archaeology, economics, political science, and psychology.

The various aspects of climate, such as rainfall, drought, and temperature, were all examined and cross-analyzed with various forms and degrees of violence in broad categories. The factors were divided into the following groups with specific associations to historical events: personal violence and crime like murder, assault, rape, and domestic violence; intergroup violence and political instability like civil wars, riots, ethnic violence, and land invasions; and instructional breakdowns like abrupt and major changes in governing institutions or the collapse of entire civilizations.

The studies were performed in both a laboratory and in natural everyday human situations, finding increases as high as 16 percent in anything hostile from horn-honking to domestic violence, assault, rape, and murder during periods of hotter climates. In fact, out of all of the 27 modern-day societies studied, every single one showed a relationship between higher temperatures and violence. A temperature rise of just 2°F, in fact, could increase intergroup conflicts, such as civil wars, by over 50 percent.

How did the scientists figure out that heat makes us angrier, especially in designed studies? In one of the studies analyzed, researchers purposely caused traffic at a high temperature at an intersection in Phoenix in order to see whether drivers without air conditioning were more likely to honk angrily than drivers in climate-controlled vehicles. Results showed that, indeed, those that were hotter honked more.

"There is considerable evidence that when people are uncomfortably hot, they become more physically aggressive," said Craig A. Anderson, an Iowa State University psychology professor who studies violence but was not involved in the study. "They tend to interpret minor annoyances as being more serious and intentional provocations than they would in comfortable temperatures."

"We often think of modern society as largely independent of the environment, due to technologist advances," wrote Edwart Miguel, co-author of the UC Berkeley analysis. "But our findings challenge that notion."