The idea of a connection between conflict and climate change is fairly new, and one that had been mostly relegated to academic journals until earlier this year. Then, in June, U.N. Secretary-General Ban Ki-moon went on record to suggest global warming as a cause for the fighting in the Darfur region of Sudan. He pointed out that warming in the tropical and southern oceans, fueled in some part by climate change, led to a decades-long drought and clashes between herders and farmers over the degrading land. When a rebellion broke out against the central government, Sudan's leaders fought back by arming and supporting the herders against the farmers—and the entire region fell into war.

Other early hot spots for warming-related conflict are likely to be in sub-Saharan Africa, Central Asia, or the Caribbean—places where institutions are weak, infrastructure is deficient, and the government is incompetent or malevolent.

And Canada and Denmark take turns pulling up each other's flag on Hans Island, a stretch of icy rock the size of a football field. These countries may be arguing over small fries right now, but what happens when oil is at stake?

David Zhang, a professor at the University of Hong Kong, scoured China's dynastic archives for records of war and rebellion and compared them with historical temperatures in the Northern Hemisphere. In the span between the 11th and 20th centuries, Zhang counted 15 periods of intense fighting. All but three of them occurred in the decades immediately following a period of unusual cold.

In his study, Zhang saw a lag of 10 to 30 years between the temperature shifts and the outbreaks of war—it takes time for a society to deplete its resources and for tensions to build.

In the modern world, it will be the poor countries that suffer the first serious effects.

Drought-stricken Australia can spend billions on wind and solar-powered desalinization plants, but the Pakistanis who rely on melting glaciers for their water supply will be able to do nothing but suffer the shortages.

In Darfur, the drought has eased, but water remains scarce; now U.N. officials are scratching their head over how to provide each of the planned 26,000 peacekeepers with at least 85 liters a day. (Meanwhile, humanitarian groups struggle to provide the displaced with enough water for drinking and cooking.)