There is strong causal evidence linking climatic events to human conflict, says a new study. (Reuters)
The research from the University of California, Berkeley, in the United States, suggests that, as global temperatures increase, by the end of the century intergroup conflicts such as civil wars and riots could increase by more than 50%.
The study, published in the journal Science on August 1, found a significant statistical link between changes in climate and personal violence such as murder, assault and rape; inter-group violence; and institutional breakdowns, from major changes in governing institutions to the fall of empires.
The research found "strong causal evidence linking climatic events to human conflict … across all major regions of the world", the authors write in the paper titled "Quantifying the Influence of Climate on Human Conflict", which spans events from 10 000 BCE to the present.
Current climate-change estimates predict an average 2°C increase in global temperatures before the end of the century, but a 2007 report by the United Nations' Intergovernmental Panel on Climate Change forecast that world temperatures could rise by between 1.1°C and 6.4°C.
Although there has been a great deal of research into changing climates and human conflict, "the research stems from disparate research fields ranging from climatology, archaeology and economics to political science and psychology", the paper says.
"What was lacking was a clear picture of what this body of research as a whole was telling us," said lead author Solomon Hsiang, assistant professor of public policy at the university's Goldman School of Public policy. "We collected 60 existing studies containing 45 different data sets and we reanalysed their data and findings … The results were striking."
Personal violence, intergroup violence and institution breakdown all exhibited "systemic and large responses to changes in climate, with the effect on intergroup conflict being the most profound", the article said. "Conflict responded most consistently to temperature, with all 21 out of 21 studies of modern societies finding a positive relationship between high temperatures and greater violence."
This echoes the findings of a study published in Proceedings of the National Academy of Science last year, titled Climate Variability and Conflict Risk in East Africa 1990-2009. Researchers from Colorado University in the US analysed a "conflict database that contains 16 359 individual geolocated violent events for East Africa from 1990 to 2009", the authors write. "The relationship between temperature and conflict shows warmer than normal temperatures raise the risk of violence."
However, Halward Buhaug, research director and professor at the Peace Research Institute in Oslo told the Mail & Guardian: "Rather than being an exhaustive meta analysis, the authors apparently selected only a subset of the indicators used in the surveyed studies and ignore several variables that were considered statistically insignificant in the original analysis."
But the big question is why violence increases. "Say you look at the data on car accidents and you see that they become more frequent on rainy days," Hsiang says. "Does that mean that rain is the only [factor] responsible for accidents? Of course not. Driver error ultimately causes accidents, but rain can make it more likely. Similarly, violent conflicts might occur for a variety of reasons that simply become more likely when climatic conditions deteriorate."
Some possible reasons include economic conditions, the need to protect increasingly scarce resources, and physiological responses to climate change.