Climate change could be to blame for many of the wars in China during the past millennium, says an article published recently in Human Ecology. The study, the first quantitative examination of the link between conflict and temperature changes, is a milestone in climate change research.

David Zhang and co-authors compared the 899 wars that occurred in eastern China between A.D. 1000 and 1911 with climatic data for the same period. They found that warfare frequency in eastern China—particularly in that region’s southern part—correlated strongly with temperature oscillations. Warfare ratios in the cold phases were twice as high as in the warm phases. Furthermore, almost all dynastic changes and warfare peaks coincided with cold phases.

“In general, rebellion was the dominant category of war,” write the authors. “The rebellions were predominantly peasant uprisings induced by famine and heavy taxation, since farmers were always the first to suffer from declining agricultural production.”

The authors surmise that by affecting agriculture, cooler temperatures disrupted food supply, especially in the ecologically vulnerable northern part of eastern China. Food scarcity could have triggered rebellions or forced people to migrate, further exacerbating food shortages in certain areas. Migration could also have generated tension between groups, producing local conflicts—especially when China was populated by nomadic tribes that could move freely. The authors also hypothesize that food scarcity may have encouraged opposing Chinese armies to conduct cross-border raids on each other’s crops. However, additional, more detailed analysis of the pathways leading from cooler temperatures to conflict in eastern China is needed.

It is unclear whether the correlation observed by Zhang in eastern China will hold true for other parts of the world. We should also be careful not to use this one study to draw premature connections to today’s unprecedented climate change. However, we hope additional quantitative studies will be carried out; they would be solid contributions to the research on climate and security, which currently suffers from a scarcity of empirical data.