March 12, 2014, by Tim Radford
FOR IMMEDIATE RELEASE
Scientists have unearthed possible evidence that climate change played a role in the expansion of the Mongol empire of Genghis Khan. They say an exceptionally warm period promoted grass growth, vital for the Mongols’ legendary horses.
LONDON, 12 March – Climate change – already implicated in the fall of Bronze Age civilisations in the Mediterranean and in the Indus Valley – may also account for the rise of one of the most fearsome empires in history.
US researchers mapping the pattern of rainfall in medieval Mongolia think they may have identified a season of plenty that put Genghis Khan on the road towards world domination.
Archaeologists and climate scientists have identified sustained drought as a reason for the fall of the Minoan civilisation in Crete, and the decay of the Harappan culture in 1,000 years earlier. But a team from Columbia University report in the Proceedings of the National Academy of Sciences that annual growth rings in a trove of stunted larches and Siberian pines in the Khangai mountains of Mongolia tell a different story.
The seasonal growth rings record a chronicle of harsh dry centuries dating back to 658AD. But between the years 1211 to 1230, something unusual happened.
Rain fell, and central Mongolia had one of the wettest periods in its history. The same period was unusually warm. Since those years coincide with the rise of the Mongol empire the connection suggested itself immediately: the Mongols were herdsmen and nomads.
Wet and warm weather means plenty of grass. Suddenly, tribesmen who wandered far to find grazing space had a surplus of feed, and soon of animals, including a glut of war horses and cattle.
The Mongol cavalry were famous for their horsemanship. “The weather may literally have supplied the Mongols with the horsepower they needed to do what they did,” says Neil Pederson of Columbia’s Lamont Doherty Observatory.
For a brief period, the Mongols, led by a commander of remarkable military and political genius, and then by his descendants, conquered and ruled most of modern Russia, Korea, China, Persia, India, the Middle East and eastern Europe.
There is never just one reason for a civilisation’s rise or fall, and historians have also argued that the Mongol invasions might have been driven instead by hunger and poverty in the Mongol heartland.
So the researchers would like to back up their tree ring evidence with studies of lake sediments, analyses of historical documents and so on, to establish that the steppes really could have provided for the great khan and his horde. The jury is still out.
The tree rings also show that after the first growth of the Mongol empire, the climate returned to its normal cold dry state. In the last 40 years, temperatures have risen. And since 1990, the country has experienced a series of devastating summer droughts often followed by a more than usually long cold winter.
Modern day drought
After the last such, an estimated eight million animals died, herdsmen became impoverished, and the poorest have moved to the capital of Ulaanbaatar, which is now home to half of the nation’s 3 million people.
“That last big drought is an example of what may happen in the future, not just in Mongolia but in a lot of inner Asia,” says Pederson. “The heat is a double whammy – even if the rainfall doesn’t change, the landscape is going to get drier.”
The potential consequences for modern Mongolia, the authors warn, could be severe.- Climate News Network
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.