Chinese history is replete with the rise and fall of dynasties, but researchers now have identified a natural phenomenon that may have been the last straw for some of them: a weakening of the summer Asian Monsoons.
Such weakening accompanied the fall of three dynasties and now could be lessening precipitation in northern China. Results of the study, led by researchers from the University of Minnesota and Lanzhou University in China, appear in the journal
Science. The work rests on climate records preserved in the layers of stone in a 118-millimeter-long stalagmite found in Wanxiang Cave in Gansu Province, China.
© Zina Deretsky, National Science Foundation
Asian monsoons, Northern Hemisphere temperatures and alpine glacier data across 1,800 years are compared.
By measuring amounts of the elements uranium and thorium throughout the stalagmite, the researchers could tell the date each layer was formed. And by analyzing the "signatures" of two forms of oxygen in the stalagmite, they could match amounts of rainfall--a measure of summer monsoon strength--to those dates.
