ELIZABETH JACKSON: Researchers at the University of California in Berkeley have just published a paper in the journal Science, suggesting a causal link between climate change and violence.
The researchers argue that even small rises in temperature result in significantly more civil conflicts as well as assaults, rapes and murders.
Madeleine Morris is speaking here to one of the lead researchers, Marshall Burke.
MARSHALL BURKE: What we find is that a one standard deviation increase in temperature leads to about a 10 to 15 per cent increase in many different types of civil conflict.
So in parts of sub-Saharan Africa, a standard deviation in temperature is about 0.3 or 0.4 degrees Celsius. If you average across the United States, it's more like three degrees.
MADELEINE MORRIS: But if we're talking about areas in Africa and certainly in parts of Australia which share a lot of the same latitude as Africa, that's really a very small increase in temperature to see a very significant increase in violence.
MARSHALL BURKE: That's what was so surprising to us: that these relatively small deviations from normal temperatures - and we also see it for rainfall, small deviations from normal rainfall - lead to these pretty large increases in many different types of conflict.
MADELEINE MORRIS: The big question is why? Do you know why?
MARSHALL BURKE: So if you think about developing countries in particular that depend on agriculture for their livelihoods, we know that agriculture is very sensitive to changes in climate, so a very hot year or a very dry year, when crops wither and die, poor people who depend on agriculture can become desperate and in the absence of other alternatives, they might take up arms.
Another explanation: so when we look at certain types of conflict - and these are kind of personal conflict, things like assaults and murders - the paper seems to suggest that this might be due to a real kind of physiological response on the part of humans to really high temperatures.
So on a really hot day, you often feel sort of grumpy, and what our results show is you find pretty large aggregate of effects of very hot temperatures on different types of violence. So this grumpiness actually, for some people, translates into more aggressive action and to violence.
MADELEINE MORRIS: If we were to see a two degree rise in global temperature, what then would be the effect?
MARSHALL BURKE: So one thing we want to be careful about is, societies in the future might be able to respond to climate better than we can today. But taken at face value, if we just assume that future societies will respond to temperature as current societies have, then we could see a 50 per cent or greater increase in civil conflict in sub-Saharan Africa as a result of climate change by about 2050.
But developed countries, most rich countries, do not experience civil wars any more, thankfully. But what they do experience, and especially in the US, we experience a lot of violent crime.
So what these studies suggest is that as temperatures increase in the future and we have increased exposure to extreme heat, it's highly likely that we'll see more violent crime.
ELIZABETH JACKSON: Marshall Burke, lead researcher on that study, speaking there to AM's Madeleine Morris.