Sudden change in climate ‘helped Genghis Khan rise to power’

In the rings of ancient and gnarled trees, a team of scientists has found evidence of a period of consistent warmth and wetness in Mongolia between 1211 and 1225 - the exact time that Genghis Khan rose to power.

Coincidence? They think not.

This unusual stretch of mild temperatures and heavy rain in an area traditionally known for its cold and arid climate would have increased the productivity of grasslands in the Mongolian steppe, the researchers say. The abundant grass would in turn increase the number of grazing animals that could live off it.

Members of Genghis Khan's army reportedly had five horses apiece, which allowed them to swiftly conquer an enormous area that stretched from East Asia to eastern Europe, as well as parts of northern India and the Middle East. They also travelled with a herd of livestock that provided them with food.

"I think of it as nature set the table, and Genghis Khan came to eat," said Amy Hessl, a tree-ring scientist at West Virginia University, in a video describing the research published on Monday in the Proceedings of the National Academy of Sciences. "He didn't have to come eat, and he didn't have to eat the way he did, but the table was set and it was a matter of whether or not the culture and the people capitalised on that."

Her colleague Neil Pederson of Columbia University's Lamont Doherty Earth Observatory put it this way: "Grass was the power of the day."

The story of the unusual wet period in Mongolian history was written in ancient Siberian pine trees that Pederson and Hessl first sampled on a whim during a research trip in 2010. The trees were growing on a nearly soil-less lava field in central Mongolia, dotted with horse skeletons. The researchers said that because the trees are severely water stressed, they are especially sensitive to changes in the weather.