MINNEAPOLIS, Nov. 11 (UPI) -- U.S. and Chinese scientists say they've discovered a linkage between the cyclical weakening of Asian monsoons and the fall of Chinese dynasties.
Scientists from the University of Minnesota and China's Lanzhou University said a weakening of the summer Asian monsoon season accompanied the fall of the Tang, Yuan, and Ming dynasties.
The work rests on climate records preserved in a 1,810-year-old stalagmite found in a Gansu Province cave in China. By measuring amounts of uranium and thorium in the stalagmite, the researchers could determine the date each layer formed. And by analyzing the "signatures" of two forms of oxygen in the stalagmite, they linked amounts of rainfall -- a measure of summer monsoon strength -- to those dates.
"Summer monsoon winds originate in the Indian Ocean and sweep into China," said Hai Cheng, corresponding author of the paper and a researcher at the University of Minnesota. "When the summer monsoon is stronger, it pushes farther northwest into China."
Those moisture-laden winds, said Cheng, bring rain necessary for cultivating rice. But when the monsoon is weak, winds stall farther south and east, depriving northern and western China of summer rains, thereby contributing to social upheaval and perhaps the fall of dynasties.
The research is reported in the journal Science.
