Hot, sticky and miserable weather brings out the bear in almost anyone. Who hasn't lashed out at children, friends, pets and significant others when the temperature heats up?

While this connection between weather and mood may seem like a small-scale, personal problem, with global warming, it may carry much more serious consequences.

A compelling new study, carried out by teams at the University of California, Berkeley, and Princeton University and published in the journal Science, measured how climate can affect our behavior in considerable — and negative — ways.

These are moderate changes, but they have a sizable impact on societies.

The researches reviewed 60 earlier studies from the present all the way back to 10,000 BC to see whether outcomes varied along with temperature. They looked at the relationship between weather patterns like heat, drought, and rainfall with the frequency of violence in three categories: personal violence (domestic violence, rape, assault), intergroup violence (like civil war, riots, and ethnic violence), and institutional violence (major changes in government and breakdowns of civilizations).

“The results were striking, ” said study author Solomon Hsiang in a news release. All three of the different types of violence were linked to climate change — either increases in temperature or extreme rainfall. For example, when temperature rose by one standard deviation from the average in an area, there was a 4% rise in personal violence and a 14% rise in intergroup conflict.

“For a sense of scale,” said author Marshall Burke, “this kind of temperature change is roughly equal to…warming a United States county by 3°C (5°F) for a given month. These are moderate changes, but they have a sizable impact on societies.”

Studies over the past several decades have found that as temperatures go up, so does violence. The reasons for the broader connections seen in this study aren’t totally clear, but it’s likely to be a combination of factors. It could be, for example, that climate may affect a country’s resources, and therefore its economy, which could trigger acts of violence, revolt, and so on.

It could also be something more immediate – perhaps just the extra stress that high temperatures put on the body. “The studies showing that high temperature increases violence crime in the USA and other wealthy societies seems to suggest that physiological responses are important, too, with very short-run exposure to heat contributing to more aggressive and violent behavior,” said Burke.

Although we think of ourselves as being far removed from the environment – perhaps too "civilized" to be affected by it – the reality is quite different, the authors point out. It may be a while before we fully understand the relationship between weather and behavior, but since the earth seems to be heating up, the results are relevant.

Surface temperature is projected to increase by several degrees by just 2050. According to Burke, the results of the study suggest that, “A global temperature rise of 2 degrees Celsius could increase the rate of intergroup conflicts, such as civil wars, by over 50 percent in many parts of the world.”

For all these reasons, it’s important to do what we can to lessen global warming (by reducing our individual footprints) while at the same time putting significant energy into addressing violence in our own country and abroad.