People who live in places with a varied climate are generally less violent than those who live in consistently hot areas, according scientists who have been trying to explain why violent crime is often higher near the equator.

Several studies have shown that levels of violence and aggression are higher in hotter countries, but according to the scientists, the leading theories are incomplete.

One model, known as the Routine Activity Theory, suggests that people are outside more in warm weather. However, this does not explain why there is more violent crime when it is 35C, rather than 25C.

Another model, the General Aggression Model, suggests that high temperatures make people uncomfortable and irritable.

But Brad Bushman, a co-author of the new study, says the analysis fails to explain more extreme acts such as murders.

Instead, researchers at Ohio State University and Vrije Universiteit Amsterdam have proposed a theory called CLASH, which stands for Climate Aggression and Self-control in Humans. The model suggests that it is not simply the heat that leads to an increase of violent crime, but also the lack of seasonal variation.

In climates which are hot and remain similar throughout the year, there is less need to prepare for lean times. For example, there is no need to hoard food, or prepare firewood for the winter. This dictates how much a culture values time and self-control.

This allows people who live in warm climates to have a "faster life strategy", in which they are freer to do what they want in the moment and are less concerned about the future.

The researchers argue that this strategy explains why people who live near the equator have babies earlier and more often. They also state that with less self-control, people are quicker to react aggressively.

The findings of the report could be contested by some warm climate countries, particularly Qatar, the United Arab Emirates and Singapore, which have some of the lowest crime rates anywhere in the world.

Professor Paul van Lange, lead author of the study, says his findings do not mean that people in hot climates always have to be violent.

"How people approach life is a part of culture and culture is strongly affected by climate. Climate doesn’t make a person, but it’s one part of what influences each of us. We believe it shapes the culture in important ways."