An exhaustive study of a wide range of conflicts over thousands of years has found that rising temperatures are inevitably linked to an increase in violence.

According to Climate News Network, three US scientists have analysed 60 studies by 190 scholars published in 26 journals of 45 different conflicts around the world.

They concluded that with every significant shift in temperature there was an increased risk of social or societal violence, and have published their findings in the journal Science.

The studies were drawn from climatology, archaeology, economics, political science and psychology. A common statistical framework was used to examine the pattern of outcomes and it was found that increased temperature or extended drought were significant factors.

The authors specifically looked to see if there could be a link between climate and conflict within three different categories.

These included personal violence such as assault, murder and domestic violence; intergroup violence and political instability; and institutional breakdowns such as abrupt changes in government. They found a connection in all three types of conflict.

Conflict responded most consistently to temperature – of 21 studies of modern societies, all 21 showed a positive relationship between higher temperatures and raised levels of violence.

A separate research paper in Science warns that global average temperatures could increase by 2°C between 2046 and 2065, and by 4°C between 2081 and 2100.

Because a study of contemporary and historic conflict required the researchers to identify common factors in very different cultures in very different latitudes, they chose a statistical yardstick called a standard deviation: the difference from the normal, or average.

One standard deviation would be the equivalent to a warming of a country in Africa of 0.4°C for an entire year, or the warming of a US county by 3°C for a given month.

According to co-author Marshall Burke from the University of California at Berkeley, one standard deviation shift towards hotter conditions causes the likelihood of personal violence to rise 4% and intergroup conflict to rise 14%.

His colleague Edward Miguel said: “We often think of modern society as largely independent of the environment, due to technological advances, but our findings challenge that notion.”

Quite how climate links with conflict may differ in each case, they pointed out. For instance, in poorer rural countries drought and extreme heat affect harvests and thus food prices in city markets.

In the developed world however, crowded cities and hot nights mean more opportunities for sudden flashes of violence between different communities.

Maxine Perella

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