When farming fails, fighting starts.Corbis

Most of the armed conflicts in eastern China over the past 1,000 years were triggered by food shortages caused by climate, say researchers.

The finding lends weight to the idea that future climate change, resulting in water and food shortages, might have similar effects, says Earth scientist David Zhang, of the University of Hong Kong. "Regions with rich resources and those lacking resources could be hot spots for conflicts."

Between 1000 and 1911, there were 899 wars in eastern China, where most of the country's food is grown. Zhang's team classified each decade as a time of either very high (more than 30 wars), high (15-30 wars), or low (less than 15 wars) conflict.

Over the same period, climate data for the Northern Hemisphere show six major cycles of warm and cold phases. Crop and livestock production dropped significantly during the cold phases.

All four decades of very high conflict, and most periods of high conflict, coincided with cold phases, they found. Warfare generally lagged 10-30 years behind the start of a cold phase.

"In situations of ecological stress, warfare could become the ultimate means of redistributing shrinking resources," the team writes in Human Ecology¹.

"The result surprised me very much," says Zhang. "All high war periods and dynastic changes occurred during cold periods. I felt that human beings were still animals."

Rising tensions

The match between climate and warfare "would seem to make perfect sense", says economist Gary Yohe of Wesleyan University in Middletown, Connecticut, a contributor to the most recent Intergovernmental Panel on Climate Change.

He agrees that migrations or shortages brought on by climate change could lead to increased tensions and warfare. "The potential for human conflict within and across national boundaries is certainly something that climate change could exacerbate," he says. "There is a long history of nation states invading other nation states for natural resources."

Recently, a United Nations report declared that climate change was one of the causes of the conflict in Darfur, although experts on the region have criticized this conclusion as being too simplistic (see 'Darfur's climate roots challenged')

Sinologist Rudolf Wagner of the University of Heidelberg in Germany says that poor growing weather would be one of several contributing factors for war in China. "In extreme cases, I think there is definitely something to it."

But, he adds, organizational, social and political factors — such as whether governments could control their territory, and how they treated their people — are also important. "The paper is interesting but I think a bit overdone," he says.

Zhang, however, believes that the strife-inducing effect of cold weather was probably not confined to China. "In the coldest period of the Little Ice Age, we can find the general crisis of the seventeenth century in Europe, Japan, Korea and the Ottoman Empire," he says.

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• References

  1. Zhang, D. D., Zhang, J., Lee, H. F. & He, Y.-Q. Hum. Ecol. 35, 403-414 (2007).