Global warming, more wars? Climate could spark more conflict, study says.

Peacemakers are likely to be in great demand by 2050 if global warming proceeds unabated.

That is the implication of a new analysis exploring the links between climate change and conflict. The work represents the first attempt to survey a burgeoning number of studies on the subject to see if they point in a common direction and to quantify the overall effect the studies identify, researchers say.

The scientists conducting this "metastudy" estimate that if greenhouse-gas emissions from human industrial activity follow the business-as-usual path, and especially if people respond to changing climate in the future in much the same way they have throughout human history, warmer temperatures could significantly increase the risk of tribal, ethnic, or civil wars, as well as battles between countries.

The largest increase in risks appears in countries in the tropics, where people are expected to bear the brunt of climate change, the researchers note. Significantly warmer temperatures and increases in extreme rainfall could push the risk of so-called group conflict up by 56 percent over today's risk. The risk of friction among individuals could rise by 16 percent, the study implies.

They also point to a change in relative risk since 1950, after which changes in temperature have emerged as a higher risk factor than changes in precipitation, and the risk of group violence is greater than the risk of person-to-person conflict.

The researchers caution that climate clearly is not the only factor at work. Not all climate events affect all conflicts. Nor does a changing climate alone determine whether conflicts will occur.

Still, "for a long time, people have been arguing: Is there an effect or not, yes or no?" says Solomon Hsiang, a researcher at the University of California, Berkeley who focuses on sustainable development and the effects of climate on societies.

The answer is yes, says Dr. Hsiang, who along with two colleagues from Princeton University and Berkeley conducted the analysis. The results are set to appear in Friday's issue of the journal Science.

The new questions, he continues, are why, and how heavily does climate influence conflict compared with other influences, such as personal or national wealth, political stability within a region or country, or how governments respond to migration within or across their national borders.

Other researchers exploring the links between climate, social, economic, and political conditions and conflict say the new study overstates climate's effect on the risk of conflict.

John O'Loughlin, a geographer at the University of Colorado at Boulder who explores the interplay of environmental conditions and conflict, notes that in his research, as in the new study, climate conditions play a role. But his own work suggests that warming temperatures or extreme precipitation are poor predictors of risk compared with the social, economic, and political drivers for conflict.

Still, the new study "really is a heroic effort. They're the first people to sit down and say: Can we make sense of this?" he says, referring to the 60 studies the team included in its analysis.

The studies span some 10,000 years of human history, "conflicts" ranging in scales from incidents of domestic violence to all-out war, and shifts in temperatures and rainfall that range from events lasting a few hours to centuries.

The studies involved criminologists, geographers, psychologists, and archaeologists who "all had been working on related issues," Hsiang says. "We set about trying to understand what everyone was finding."

The studies varied in important ways, he adds. But once his team set the studies into "a single coherent framework, we saw that people were seeing the same thing around the world."

The common thread: Higher temperatures, or higher extremes in precipitation – either more of it or less of it – "are associated with higher levels of human conflict around the world, throughout time, in different types of societies," Hsiang says.

How tightly associated, compared with other factors linked to conflict, is another issue, other researchers say.

The deepest concern about the link between climate and conflict centers on Africa, says Andrew Solow, a scientist at the Woods Hole Oceanographic Institution in Massachusetts who studies sustainable development and marine resources.

He points to a study conducted several years ago by researchers in Norway who noted that since the early 1990s, civil conflicts in Africa have declined, despite recent headlines, even as temperatures were warming and extreme rainfall or drought were rising. Factors that overwhelmed any climate effect on conflicts included the end of the cold war – with its proxy wars in Africa – and economies in many countries picking up steam, he says.

From a policy perspective, he cautions, the new study could become a distraction, diverting attention from the need to help countries in Africa grow in a sustainable way and focus on other factors that historically have helped reduce conflicts.

"It's certainly worth worrying about what will the role of climate change be in all of this. We need to be thoughtful and careful about that," he says. But if conflict is the concern, the lesson from the Norwegian and other studies is that a higher standard of living, an equitable society, and other non-climate factors "are where the attention is best placed."

Others, such as Dr. O'Loughlin, see shortcomings in the study itself that suggest the team is overreaching in its conclusions and exaggerating climate's effect on conflicts.

Still, he suggests, the team's agenda for future research on the topic is enough to make it noteworthy.

The study represents "a very valuable brush-clearing exercise," he says. "I think all future work on this topic will have to reference this paper" for the scientific road map it draws and the questions it raises.