It's increasingly clear that the consequences of climate change won't stop at just heat waves and sea-level rise. Scientists expect numerous social issues to arise around the world as well, such as food shortages, decreased water quality and forced migrations. And many experts now believe that violence, war and other forms of human conflict may be driven or worsened by the effects of climate change.

A new study, published Monday in the journal Proceedings of the National Academy of Sciences, lends support to the growing body of evidence behind this idea. The study finds that climate-related disasters may enhance the risk of armed conflict around the world — specifically in countries with high levels of ethnic divides.

"This debate comes up time and again — is climate change really something like a trigger for violent conflict?" said Hans Joachim Schellnhuber , director of the Potsdam Institute for Climate Impact Research and senior author of the new paper. "Some people say yes, others say no. There's a heated debate about it."

Many studies in the past have addressed the question of whether climate events might drive human conflict. Some of these have examined the issue on a global scale, while others have zeroed in on specific events — for instance, several studies have implicated drought as one of many factors that aided in the outbreak of civil war in Syria. Overall, multiple studies have indicated a connection between climate and conflict, although several have suggested that the link may be weak. So the concept has remained something of a controversial topic.


The new study seeks to help lay some of the debate to rest. The researchers compiled a list of armed conflicts and a list of natural disasters around the world between the years 1980 and 2010. They analyzed each disaster in terms of the amount of economic damage it caused to the nation where it occurred. They then conducted statistical tests to determine whether any of the conflicts and disasters coincided.

"What we do is not just correlational analysis, but so-called coincidence analysis, which also looks at which event is coming first and then which other one follows — so you get a certain causality," Schellnhuber explained. In other words, the tests help to indicate whether one event — say, a drought or a heat wave — might have helped trigger an event that followed it, such as an outbreak of war.

The researchers also grouped countries in terms of other nation-specific factors that might have influenced the outbreak of conflict, such as income inequality, religious divides and ethnic divides.

Altogether, they found a significant link between climate disasters and the outbreak of violent conflict specifically in countries with high degrees of ethnic fractionalization. Notably, the other factors did not seem to play an important role -- only when countries were examined in terms of their ethnic divides did climate events significantly exacerbate the outbreak of conflict. This seemed to be the case for climate disasters that caused both large and small amounts of economic damage. In all, about 23 percent of armed conflicts in highly ethnically divided nations coincided with climate-related disasters.

"We cannot explain the full complexity of the emergence of violent conflict, but here we have found something really robust, a factor that really matters," Schellnhuber said.

The authors have emphasized that their results don't necessarily suggest that climate events are the root cause behind any given conflict. Rather, they indicate that these events may increase the likelihood of violence erupting in a place that was already predisposed to conflict, or potentially serve as the final straw in an area where trouble was already brewing.

"If a society has already the sort of divisive lines, fault lines ... where, in a sense, hostility along the fault lines can emerge, then you need a triggering shock," Schellnhuber said. This is similar to the arguments that have been made in studies of specific conflicts -- for instance, research on Syria didn't identify drought as the only factor contributing to the civil war, but rather one of many issues that helped contribute to the outbreak of violent conflict.

It's important to understand the specific conditions that may predispose a region to conflict under certain climate scenarios, he noted, because this knowledge may help scientists identify areas that could be headed for trouble in the future.

"We could turn it into something like a radar system," he suggested.

The current paper only identifies regions where these factors have coincided in the past and makes no projections for the future, although the researchers have suggested that certain conflict-prone regions of the world where deep ethnic divides already exist — such as in North and Central Africa and Central Asia — are also expected to be particularly vulnerable to the future impact of climate change, making them particular regions of concern. Schellnhuber argues that predictions for the coming decades, using the type of information gathered for this study, could be a focus of future research.

"That would be the logical follow-up paper that could have a very high practical importance," he said.