Tensions between the Peruvian government and the rebel group the Shining Path erupted into bloody clashes in 1982—the same year that an El Niño-Southern Oscillation (ENSO) event scoured potato fields across the hilly nation. Doomsayers might see cause and effect, but scientists have so far struggled to connect widespread violence with global climate phenomena. Now, a new study suggests that civil strife is twice as likely to break out in many nations worldwide during El Niño years.
"More and more of the evidence is pointing toward a strong link between adverse weather or adverse climate and political violence in the world's poor regions," says Edward Miguel, an economist at the University of California, Berkeley, who was not involved in this study. "This is an important piece of evidence in that debate."
In 2009, Miguel and colleagues published a controversial paper in the Proceedings of the National Academy of Sciences, arguing that spikes in temperature had played a dramatic role in igniting African civil wars. While some scientists criticized the study's statistical methods, many questioned its basic claim, says Solomon Hsiang, lead author of the new study, who studies the confluence of political and climate science at Columbia University. The question, Hsiang says, became, "Is it at all possible that global climate can affect conflict?" Scientists, he adds, don't have the know-how to turn the thermostat up or down on the planet and then sit back to watch how angry people get.
But the planet does flip from hot to cold naturally: every few years as waters in the tropical Pacific cool, during La Niña events, or heat up, during El Niño years. These rapid, periodic shifts in climate, Hsiang and his colleagues realized, might make a good proxy for studying how climate might impact war around the world.
So the team examined 234 clashes each claiming more than 25 lives between governments and rebel groups across the globe from 1950 to 2004. In the tropical nations most affected by ENSO swings, such as Peru, the Sudan, or India, the likelihood of civil violence erupting doubled during El Niño years, from about 3% to 6%, amounting to an extra 48 clashes, the group reports online today in Nature. In nations separated from the steep climatic shifts associated with ENSO events, including the United States, France, and China, the chances of civil strife remained at a steady low of 2%. But just how El Niño events fanned the flames in what were largely the world's poorest nations is unclear, Hsiang says.
Such a relationship between climate swings and political instability seems, at least anecdotally, to have a long history, says Thomas Homer-Dixon, a nature and society researcher at the University of Waterloo in Canada: "What we're seeing is a modern-day manifestation of a phenomenon that goes back millennia." The city of Angkor in modern Cambodia, for instance, known for its web of monsoon-fed irrigation canals, fell to invaders in the mid-15th century. A series of droughts began to dry up those famous canals during the same period in history. As Hsiang and colleagues found, those societies most at the whim of climate tended to also be the nations with economies still rooted in agriculture, Homer-Dixon notes.
But Halvard Buhaug, an international relations specialist at the Centre for the Study of Civil War in Oslo and a sharp critic of Miguel's 2009 study, doesn't see cause and effect just yet. "I still believe that socioeconomic and political factors are the most important, common drivers of civil wars," he says. "But the intriguing finding ... certainly deserves further scrutiny." Without knowing how exactly climate swings can lead to violence, if at all, he says, it becomes an uphill battle for humanitarian organizations to direct preventative measures.