Marshall Burke, from the University of California, Berkeley, said: "This is a relationship we observe across time and across all major continents around the world. The relationship we find between these climate variables and conflict outcomes are often very large."

The researchers looked at 60 studies from around the world, with data spanning hundreds of years. They report a "substantial" correlation between climate and conflict. Their examples include an increase in domestic violence in India during recent droughts, and a spike in assaults, rapes and murders during heatwaves in the US.

The report also suggests rising temperatures correlated with larger conflicts, including ethnic clashes in Europe and civil wars in Africa. Yet, Burke said: "We want to be careful, you don't want to attribute any single event to climate in particular, but there are some really interesting results."

"There is lots of evidence that changes in economic conditions affect people's decisions about whether or not to join a rebellion, for example." But he said there could also be a physiological basis, because some studies suggest that heat causes people to be prone to aggression. "It is a major priority for future research to distinguish between what is going on in each particular situation."

The scientists say that with the current projected levels of climate change the world is likely to become a more violent place.

They estimate that a 3.6F rise in global temperature could see personal crimes increase by about 15%, and group conflicts rise by more than 50% in some regions.