Slate: Global Cooling is Dangerous

Two decades ago, the rains in southern Sudan began to fail. According to U.N. statistics, average precipitation has declined some 40 percent since the early 1980s. Scientists at first considered this to be an unfortunate quirk of nature. But subsequent investigation found that it coincided with a rise in temperatures of the Indian Ocean, disrupting seasonal monsoons. This suggests that the drying of sub-Saharan Africa derives, to some degree, from man-made global warming.

But a look back through the last thousand years shows how quickly even a mild, natural shift in the climate can produce a period of cataclysmic violence. 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. Plunging agricultural yields, Zhang concluded, led to famine, rebellion, and war. He also found that dynastic collapses tended to follow the oscillations of the temperature cycle.