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In his popular 2008 book Climate Wars, the US journalist and military historian Gwynne Dyer laid out a daunting scenario. Climate change would put growing pressure on fresh water and food over the coming century, he wrote, triggering social disorder, mass migration and violent conflict.

But is there real proof of a link between climate change and civil war — particularly in crisis-ridden parts of Africa — as many have claimed?

No, says Halvard Buhaug, a political scientist with the Peace Research Institute Oslo in Norway. In research published today in Proceedings of the National Academy of Sciences1, he finds virtually no correlation between climate-change indicators such as temperature and rainfall variability and the frequency of civil wars over the past 50 years in sub-Saharan Africa — arguably the part of the world that is socially and environmentally most vulnerable to climate change. “The primary causes of civil war are political, not environmental,” says Buhaug.

The analysis challenges a study published last year that claimed to have found a causal connection between climate warming and civil violence in Africa. Marshall Burke, an economist at the University of California, Berkeley, and colleagues, reported a strong historical relationship between temperature and the incidence of civil war. They found that the likelihood of armed conflict across the continent rose by around 50% in unusually warm years during 1981-20022. Projected future warming threatens to offset the positive effects of democratization and eradicating poverty in Africa, they warned.

Data-set discord

The two rival groups are now disputing the validity of each other’s findings.

Buhaug says that Burke’s study may have been skewed by the choice of climate data sets, and by their narrow definition of ‘civil war’ as any year that saw more than 1,000 fatalities from intra-national conflict. The definition is at odds with conventional measures of civil war in the academic literature, says Buhaug: “If a conflict lasts for 10 years, but in only 3 of them the death toll exceeds 1,000, [Burke et al] may code it as three different wars.”

“You’d really like to apply as many complementary definitions as possible before proclaiming a robust correlation with climate change,” Buhaug adds.

Burke maintains that his findings are robust, and counters that Buhaug has cherry-picked his data sets to support his hypothesis. “Although we have enjoyed discussing it with him, we definitely do not agree with Halvard on this,” says Burke. “There are legitimate disagreements about which data to use, [but] basically we think he’s made some serious econometric mistakes that undermine his results. He does not do a credible job of controlling for other things beyond climate that might be going on.”

Buhaug disagrees vigorously. “If they accuse me of highlighting data sets in favour of my hypothesis, then this applies tenfold more to their own paper.”

The debate has much wider implications for policy-makers. The link between climate and civil war has been mooted several times before — for example, in a 2003 report for the Pentagon on the national-security implications of climate change; in the Stern Review on the Economics of Climate Change, prepared for the UK government in 2006; and in the United Nations’ post-conflict environmental assessment of Sudan in 2007, which suggested that climate change was a factor behind the Darfur conflict.

Given the many causes of unrest, it is not surprising that a meaningful correlation with climate is hard to pin down, says Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research in Germany. “Even if the data and methods were up to the task — which they aren’t — the currently still weak climate signals in civil wars.”

It is extremely difficult to identify simple, robust cause-and-effect relationships between changes in climate and societal outcomes, agrees Roger Pielke, a political scientist and climate policy expert at the University of Colorado in Boulder.

“The climate signals are small in the context of the broader social factors,” Pielke says. “This does not at all diminish the importance of responding to climate change, but it does offer a stark warning about trying to use overly simplistic notions of cause and effect to advocate for such actions.”

  • References

    1. Buhaug, H. Proc. Natl Acad. Sci. USAdoi:10.1073/pnas.1005739107 (2010).
    2. Burke, M. B. et al. Proc. Natl Acad. Sci. USA 106, 20670-20674 (2009).

Nature News, 6 September 2010