CLIMATE

Monsoons shaped dynasties’ fate?

Monsoons may have played a role in the rise and fall of Chinese dynasties, a new study finds.

Researchers from the University of Minnesota in Minneapolis and Lanzhou University in China, led by R. Lawrence Edwards, have reconstructed 1,810 years of the Asian monsoon, moisture-laden winds that blow north from the Indian Ocean bringing rain to many Asian regions, especially India and China. The winds bring with them the rain needed for a bountiful growing season.

Edwards and colleagues looked at a stalagmite, a rock column formed by the solidification of minerals from water, that had grown continuously from 190 to 2003 A.D. a kilometer inside the Wanxiang Cave in China. They first measured uranium and thorium in the stalagmite to date the different layers, and then measured the ratio of two different isotopes of oxygen in the stalagmite. The source of oxygen was dripping water from the cave roof which in turn came from the rain, and a measure of the ratio helped them calculate the rainfall during a particular time period.

They found that a drop in monsoon rains coincided with the declines of three dynasties. Rainfall was low between 850 and 930 A.D., spanning the time when the Tang dynasty declined and collapsed. This time also coincided with dry weather in the Americas and the demise of the Mayans. Similar dry periods in the late 14th and early 17th centuries coincided with the demise of the Yuan and Ming dynasties.

A period when the monsoon was strong – between 960 and 1020 A.D. – was a “golden age” in China when the Northern Song dynasty flourished, the population doubled and rice cultivation expanded.

BOTTOM LINE: There is evidence suggesting that climate played a role in the rise and fall of Chinese dynasties. CAUTIONS: This is the first study of its kind and more work is needed to confirm these findings. WHAT’S NEXT: Researchers will look further back in history to see if the same trend appears. WHERE TO FIND IT: Science, Nov. 7