What was done
Historians typically point to political, economic, cultural and ethnic unrest as the chief causes of war and civil strife. In the present study, Zhang et al. argue that changes in climate play a key role as well; and to examine their thesis, they compared proxy climate records with historical data on wars, social unrest and dynastic transitions in China from the late Tang to Qing Dynasties (mid-9th century to early 20th century).
What was learned
War frequencies, peak war clusters, nationwide periods of social unrest and dynastic transitions were all significantly associated with cold as opposed to warm phases of China's paleotemperature reconstructions. More specifically, all three distinctive peak war clusters (defined as more than 50 wars in a 10-year time period) occurred during cold phases, as did all seven periods of nationwide social unrest and nearly 90 percent of all dynastic changes that decimated this largely agrarian society. As a result, the authors conclude that climate change was "one of the most important factors in determining the dynastic cycle and alternation of war and peace in ancient China."
What it means
Historically, warmer climates have been much more effective than cooler climates in terms of helping to "keep the peace" in China. Based on this model, perhaps we should all pray for a little global warming to give peace a better chance worldwide.
Zhang, D., Jim, C., Lin, C., He, Y. and Lee, F. 2005. Climate change, social unrest and dynastic transition in ancient China. Chinese Science Bulletin 50: 137-144.