. and one that - perhaps surprisingly - climate scientists have been studying. New research at Columbia University in New York has found a link between civil war and unusually hot and dry conditions in tropical countries.
Presenter: Cathy Harper
Solomon Hsiang, Colombia University; Mahendra Kumar, director of the Centre of Climate Change at the University of Fiji; Andy Solow, Woods Hole Oceanographic Institution in Massachusetts
HARPER: Historians have suggested that changes in climate may have contributed to the collapse of various ancient kingdoms. Now, researchers at Columbia University are looking at whether unusually hot and dry weather conditions contribute to civil war today. A new study has found El Nino weather patterns in the Pacific Ocean double the risk of civil war across Africa, Asia and the Americas.
The report's lead author is Solomon Hsiang.
HSIANG: What we found was that when we look at tropical countries, when the globe is in its cooler and wetter La Nina state the risk of conflicts throughout the tropics was about 3 per cent per year. So that means three out of one hundred countries were to be expected to begin a new civil war. But when the global climate shifted into it's hotter and drier El Nino stage the risk of civil war rose to about 6 per cent. So that's actually a doubling. And this is actually a very large effect in absolute terms. What it means is that about one out of five civil conflicts since 1950 were in some way influenced by El Nino.
HARPER: So why is it that El Nino would cause a war?
HSIANG : When an El Nino event occurs things become hotter and drier, and agricultural sectors in societies affected suffer dramatically. So there's economic contraction, particularly in the societies that are lower income and rely more heavily on agriculture. And that sort of economic loss could translate into conflicts through a variety of mechanisms. So for example economists have put forward the idea that when labour markets are bad for workers - so when wages are down or unemployment is high it becomes a lot easier to hire people into non-civilian activity. So if you can imagine being the leader of a rebel group and you have to raise enough army to try and overthrow the government, it's actually much cheaper to do it when the economy is doing badly. .....
HARPER: Can we talk a little bit more about specifically the Asia Pacific region and what you've found in terms of El Nino on that area?
HSIANG: One thing that we did in this study is that we tried to see whether or not Africa was really driving our results, or whether it was really a true global phenomenon. So we actually threw out Africa from our data in one of our experiments and found that our main results hold. So countries in South East Asia, in South Asia and Oceania, in those regions, we observed that the same pattern holds. So countries such as Indonesia, and Myanmar and India have had conflict that seem like they are associated with El Nino.
HARPER: Mahendra Kumar is the director of the Centre of Climate Change at the University of Fiji.
He says in the case of the Pacific, El Nino certainly leads to more cyclones, which often cause crop failure.
KUMAR: Of course that could be a trigger for behaviour which could lead to conflict. The 1997-98 - in Fiji the drought actually wiped out two thirds of our sugar industry But it may be very premature to suggest that these events led to any national conflict.
HARPER: Andy Solow is a statistician at the Woods Hole Oceanographic Institution in Massachusetts in the United States. He wrote a commentary that accompanied Columbia University's study.
SOLOW: It's main value ... It's a statistic study so it's not based on any particular model or understanding of human dynamics that lead to civil conflict it's just a kind of a correlational study but the result is quite robust. And so one thing that it ought to do is to lead a more focused complimentary research on the nature of these conflicts and their connections to the weather and if we can understand that better then it may be possible to intercede in some way to remove the kind of limit the kind of problem that's leading to conflict.