Washington, Nov 7 : A new study has linked the rise and fall of China's ancient dynasties with monsoon cycles, with the weakening of the natural phenomenon proving to be the last straw for the kingdoms.
According to a report in National Geographic News, the study was led by researchers from the University of Minnesota and Lanzhou University in China.
The work rests on a 2,000-year-old record of monsoon activity preserved in the layers of stone in a 118-millimeter-long stalagmite found in Wanxiang Cave in Gansu Province, China.
The climate record was preserved in a stalagmite-a rock formed by mineral-rich waters dripping onto the cave floor year after year.
The stalagmite was formed over 1,810 years; stone at its base dates from A.D. 190, and stone at its tip was laid down in A.D. 2003, the year the stalagmite was collected.
Like trees, stalagmites have annual growth rings that can provide clues about local environmental conditions for a particular year.
The team measured the amount of oxygen-18-a rare form of "heavy" oxygen-in the stalagmite growth rings.
Growth rings with large amounts of oxygen-18 indicate years of weak summer monsoons and less rain.
Comparing the stalagmite record with Chinese history, the researchers found that a period of strong monsoons was associated with the "golden age" of the Northern Song dynasty.
During that time, improved rice yields allowed the population to increase from 60 million to as many as 120 million.
Furthermore, weak monsoon seasons coincided with droughts and the declines of the Tang, Yuan, and Ming dynasties.
Weak monsoons may have helped trigger one of the most tumultuous eras in Chinese history, called the Five Dynasties and Ten Kingdoms period, according to the study.
During this time, five dynasties rose and fell within only a few decades, and China fractured into several independent nation-states.
"Climate in many cases acts like the straw that broke the camel's back," said Peter deMenocal, a paleoclimatologist at Columbia University's Lamont-Doherty Earth Observatory in New York.
"The synchrony between these cultural events and climate change events is really compelling." he added.
According to Harvey Weiss, an archaeologist at Yale University, the new study "is a brilliant analysis of the problematic coincidence of abrupt climate changes and changes in political organization."