When the mercury rises in East Africa, so does the likelihood of violence -- but wetter conditions can dampen that risk.
That's the conclusion of a study published yesterday in the Proceedings of the National Academy of Sciences. It adds to a growing body of research that attempts to understand how changes in Earth's climate affect humans' willingness to fight.
What appears to be a razed civilian structure in Um Bartumbu village. Photo by Ryan Boyette for Eyes and Ears Nuba, courtesy of ENOUGH Project
Many scientists, politicians and military leaders have warned that climate change could exacerbate existing tensions in the world's poorest and most vulnerable countries, where a shift to more extreme weather patterns could lead to agricultural collapse and resource wars.
But attempts to unravel the links between climate and conflict have produced a wide range of results, some conflicting, said the new study's lead author, John O'Loughlin, a political geographer at the University of Colorado, Boulder.
"We wanted to try and resolve the debate between those particular camps and see, is there any evidence for an additional effect [on conflict] from climate change?" he said.
To get at the question, O'Loughlin and colleagues with expertise in geography and climate science assembled a massive database that catalogs more than 16,000 individual instances of violence in East Africa between 1990 and 2009, pinpointing them by date and location. The trove includes everything from cattle raids to election violence in nine countries: Burundi, Djibouti, Eritrea, Ethiopia, Kenya, Rwanda, Somalia, Tanzania and Uganda.
Then they subjected those conflict data, along with temperature and precipitation records, to a sophisticated political and statistical analysis that analyzed the relative influence of climate and factors like population size and proximity to roads and international borders.
A clear relationship
"We tried everything to explain away a climate effect," O'Loughlin said. But in the end, the researchers saw a clear relationship emerge between climate conditions and conflict risk.
While population size was by far the biggest influence on the incidence of violence, the analysis also suggests that warmer temperatures raise the risk of conflict, while wetter conditions lower that risk.
In regions that were both unusually warm and wet, temperature seemed to be the overriding influence, the researchers said, and violence increased.
"It is a really a very interesting paper," said Ted Miguel, a professor of economics at the University of California, Berkeley. "I think this paper definitely provides very fine-grained evidence with very good data that climate can have a big impact on human conflict."
That is line with a comprehensive review of prior papers on the topic that Miguel has undertaken with a fellow Berkeley economist, Marshall Burke, and Solomon Hsiang, a postdoctoral fellow at Princeton University who published a study in Nature last year that found a link between El Niño and increased conflict risk in tropical nations (ClimateWire, Aug. 25, 2011).
Their analysis, now in review at a major journal, found "the remarkable majority of studies find results similar to this O'Loughlin piece, and similar to our earlier work," Miguel said. "There are a couple of studies that don't have those findings, but they are the exception rather than the rule."
Hsiang agreed. "It's a major contribution to assemble this high-resolution data that allow us to understand the spatial dynamics of how these conflicts move around in space, but I think it buttresses what we already understand on the link between climatic events and conflict," he said.
Hunting for the mechanisms
What is harder, experts said, is divining the mechanisms at work in areas where climate appears to exert a significant influence on conflict.
"It's actually a really hard problem," Hsiang said. "All of these things happen in a complex environment, and they're interacting with each other."
He compared it to the situation of medical doctors in the 1930s who had noticed that patients who smoked were more likely to develop lung cancer. It took decades from that initial insight for physicians to fully understand how smoking actually altered the behavior of the body's cells to produce tumors.
And that makes the current body of climate-conflict research of interest -- but not yet of much help -- to governments, aid organizations and other groups interested in developing policies to address the root causes of violence, said Cullen Hendrix, a professor of international relations at the College of William and Mary.
"We have a lot of studies that are showing statistically significant correlations, but so far, it's a literature and a body of findings in search of theoretical mechanisms," he said.
"This study helps us focus in on what matters and gives us a detailed empirical picture, but it's not yet moving us all the way to the point where we can develop and implement policy interventions based on these findings."
Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500. E&E Publishing is the leading source for comprehensive, daily coverage of environmental and energy issues. Click here to start a free trial to E&E's information services.