Why hot climate fuels aggression, violence

New York: The combination of a hot climate and less variation in seasonal temperatures leads to a faster life strategy, less focus on the future and less self-control -- all of which contribute to more aggression and violence, according to a new model that explains the link between climate and crime rates.

Many studies have shown that levels of violence and aggression are higher in hot climates, but the lead explanations of why this is so are not satisfactory, according to the researchers.

So they developed the new model CLASH (Climate Aggression, and Self-control in Humans) that they believe can help explain the impact of climate on rates of violence in different parts of the world.

"Climate shapes how people live, it affects the culture in ways that we don't think about in our daily lives," said co-author of the study Brad Bushman, Professor of Communication and Psychology at The Ohio State University in the US.

"We believe CLASH can help account for differences in aggression and violence both within and between countries around the world," he said. 

The General Aggression Model suggests hot temperatures make people uncomfortable and irritated, which makes them more aggressive. 

"But that doesn't explain more extreme acts, such as murder," Bushman said.

Another explanation is that people are outdoors and interacting more with others when the weather is warm, which leads to more opportunities for conflict. But that does not explain why there is more violence when the temperature is 35 degrees Celsius than when it is 24 degrees Celsius -- even though people might be outside under both circumstances.

The CLASH model states that it is not just hotter temperatures that lead to more violence -- it is also climates that have less seasonal variation in temperature.

"Less variation in temperature, combined with heat, brings some measure of consistency to daily life", Maria Rinderu from Vrije Universiteit Amsterdam in the Netherlands explained.

That means there is less need to plan for large swings between warm and cold weather. The result is a faster life strategy that is not as concerned about the future and leads to less need for self-control.

"Strong seasonal variation in temperature affects culture in powerful ways,” lead author of the study Paul van Lange, Professor of Psychology at the Vrije Universiteit Amsterdam added.

People living in these climates are oriented to the present rather than the future and have a fast life strategy - they do things now.

With a faster life strategy and an orientation toward the present, people have to practice less self-control, Bushman said. 

That can lead people to react more quickly with aggression and sometimes violence, said the researchers who described the new model in an online article in the journal Behavioral and Brain Sciences.

"We think it provides a strong framework for understanding the violence differences we see around the world," Bushman noted.