The question is no longer just whether climate change will kill us, but also whether climate change will make us kill each other.
Almost 25 percent of armed conflicts in ethnically divided countries occur around the same time as climate-related disasters. This is the main take-away of a new study by researchers that adds crucial data to a debate that's been simmering for several years: Is there evidence (PDF) that ties war and civil unrest to the changing climate? Another finding directly applies to this and humanity's key climate change choke points: food and water. Over the three decades ending in 2010, 9 percent of wars took place in the wake of heat waves or droughts.
Shooting wars generally require a complex web of short- and long-term causes. Anecdotal fodder abounds pointing toward extreme climate events as one of them. Syria's civil war erupted amid the area's worst drought in 900 years, though consequences of the Arab Spring were its primary genesis. Further meteorological chaos could push Venezuela's economic implosion over the edge, but the oil glut and political chaos will probably play larger roles. As early as 2007, United Nations Secretary General Ban Ki-moon touted a link between climate change and the conflict in Darfur that's killed hundreds of thousands of people.
The new study, by mostly German researchers, adds weight to the common-sense notion that, at the very least, climate-related catastrophes contribute instability to places in which neighbors already stand poised to shoot each other. The authors aren't suggesting a direct and causal relationship between weather and war, at least not yet. What they have concluded is, when looking at the record of weather and war, their coincidence is dramatically higher in countries with inter-ethnic tensions than in those without them. Ethnic division and disaster was a more potent recipe for conflict than when disaster mixed with poverty or income inequality, or even with a past propensity for conflict.
"Although we do not report evidence that climate-related disasters act as direct triggers of armed conflicts," they wrote in the Proceedings of the National Academy of Sciences, "the disruptive nature of these events seems to play out in ethnically fractionalized societies in an particularly tragic way."
The authors sorted through recent thinking about climate and conflict in Syria, Somalia, Afghanistan, and more generally, Northern Africa and the Middle East. Climate change has "the potential to amplify already existing societal tensions and stressors and thus to further destabilize several of the world's most conflict-prone regions," they write.
Previous work suggesting a link has compared conflict and the meteorological record (temperature and precipitation). The European researchers went a step further, by comparing the economic toll of disasters on gross domestic product, which they posit is a more effective measure of nation-level pain. The damages data come from reinsurer Munich Re, which logged estimates for about 18,000 "climate events" over 30 years. The record of conflicts is a database maintained by Uppsala University in Sweden, which includes 241 incidents in which more than 25 people were killed in fighting. The authors include Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research and a leading climate-science adviser to Pope Francis.
The new study subtly nods at specialists on this topic who work outside the world of scientific "peer review"—namely, the U.S. Department of Defense. The phrase "threat multiplier" is one that has lived in military-speak for many years, meaning a risk to national security that's likely to beget risk even more broadly. It gained currency in 2007 when a group of retired military leaders used it in a report linking climate change and national security. It made it into the Pentagon's 2014 Quadrennial Defense Review as a description of climate change risk.
And there it sits, winking in a bright-blue sidebar called "Significance" on page one of the new study ...
... adding teeth to the Pentagon's concern.