People living in these climates are oriented to the present rather than the future, and that can lead them to react more quickly with aggression.

A new study explains why some violent crime rates are higher near the equator than other parts of the world.

The combination of hot climates and less variation in seasonal temperatures leads to a faster life strategy, less focus on the future and lower self-control, it has found.

The researchers call the new model ‘CLimate Aggression, and Self-control in Humans’ (CLASH).

“Climate shapes how people live, it affects the culture in ways that we don’t think about in our daily lives,” said Brad Bushman, from the Ohio State University in the U.S.

“We believe our model can help explain the impact of climate on rates of violence in different parts of the world,” said Paul van Lange, from Vrije Universiteit Amsterdam (VU).

The General Aggression Model suggests hot temperatures make people uncomfortable and irritated, which make them more aggressive. “But that doesn’t explain more extreme acts, such as murder,” Prof. Bushman said. Another explanation known as Routine Activity Theory is that people are outdoors and interacting more with others when weather is warm, which leads to more opportunities for conflict.

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,” said Maria Rinderu of VU. 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, researchers said.

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, he said.

That can lead people to react more quickly with aggression and sometimes violence.

The study was published in the journal Behavioural and Brain Sciences.