In the rings of ancient and gnarled trees, a team of scientists has found evidence of a period of 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, researchers said. 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 eastern Asia to Eastern Europe, as well as parts of northern India and the Mideast. They also traveled 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.
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 scores of 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 soilless 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.
They took core samples from about a dozen trees, some of which dated back more than 1,000 years. They also found evidence of a climate narrative that they couldn't ignore. For a small stretch of time, some of the rings were visibly thicker.
"I was just excited that we had wood from the time of [Genghis] Khan," Pederson said. "And it was really the trees saying 'look how wide our rings are right here.' "
They returned two years later and those samples confirmed the initial findings: The expansion of the Mongolian empire coincided with what the trees recorded as a warmer and wetter climate than usual.
They said they are working with experts from disciplines including ecology, biology, and history to find more evidence of how the climate may have contributed to the making of the largest empire in history. Pederson said. "The climate information in the trees is just one little piece of the puzzle."
Los Angeles Times