Tree rings suggest warming may have led to Mongol conquests

Los Angeles Times : Ancient pine trees record a period of unusual raininess and warmth on the Mongolian steppe between 1211 and 1225, which coincides with Genghis Khan ‘s conquests. Amy Hessl of West Virginia University and Neil Pederson of Columbia University collected the tree samples in 2010 and 2012 and noticed a distinct period of consistent growth. They argue that the extended warm and wet climate caused an increase in productivity in the grasslands that may have allowed the Mongols to be so successful. The increased growth of the grasslands would have supported an increased population of grazing animals. Mongol soldiers were reported to have five horses each, and their armies were supplied with food from large herds of livestock that followed them. However, Hessl and Pederson admit that further examination will be necessary to directly tie the climatic variation to human history.