Science - Lamont-Doherty Study Nails Down Asian Monsoon Failures Coincident With Social Collapses

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By sampling the wood of thousands of ancient trees across Asia, scientists at Columbia University's Lamont-Doherty Earth Observatory assembled an atlas of past droughts, gauging their relative severity across vast expanses of time and space. "Global climate models fail to accurately simulate the Asian monsoon, and these limitations have hampered our ability to plan for future, potentially rapid and heretofore unexpected shifts in a warming world," said Edward Cook, head of Lamont's Tree Ring Lab, who led the study.

"Reliable instrumental data goes back only until 1950. This reconstruction gives climate modelers an enormous dataset that may produce some deep insights into the causes of Asian monsoon variability." There is some evidence that changes in the monsoon are driven at least in part by cyclical changes in sea-surface temperatures.

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The tree-ring records in the study reveal at least four great droughts that are linked to catastrophic events in history. For starters, the study suggests that climate may have played a powerful role in the 1644 fall of China's Ming dynasty.

The tree rings provide additional evidence of a severe drought in China referenced in some historical texts as the worst in five centuries. This study narrows it down to a three-year period, 1638-1641. The drought was most sharply expressed in northeastern China, near Beijing, and is thought to have influenced peasant rebellions that hastened the demise of the Ming. Another severe monsoon failure came in 1756-1768, coinciding with the collapse of kingdoms in what are now Vietnam, Myanmar and Thailand. The drought roiled political structures all the way to Siberia, and the tree rings also indicate that western India was severely affected. This drought is not documented in historical records; scientists first identified it in teak rings from Thailand, and later in Vietnamese cypress trees.

Some historians have speculated that climate must have played a role for such sweeping political changes to have happened simultaneously; fragmentary accounts suggest that dry periods may have been punctuated with devastating floods. The study appears to provide an explanation for the so-called "strange parallels" that Victor Lieberman, an historian at the University of Michigan, has spent his career studying. "It provides confirmation that there are very strong climate links between monsoon regimes in India, Southeast Asia and southern China," said Lieberman in an interview.

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http://www.terradaily.com/reports/Study_Reconstructs_Devastating_Droughts_Across_Asia_999.html