Science 322, 940–942 (2008)


China's Ming Dynasty once commanded a million-man standing army and a fleet of treasure ships. But still more powerful, suggests new research, was the Asian Monsoon. Natural fluctuations in the seasonal wind appear to have triggered the Mings' overthrow and other historic milestones — but during the last 50 years, human influences have taken over as the driver of monsoonal changes, say scientists.

In a Chinese cave on the fringes of the monsoon's range, a team led by Hai Cheng of the University of Minnesota, found a 1,810-year-old stalagmite that proffers an unusually detailed record of past monsoon seasons. By analysing a range of isotopes from the stalagmite's layers, Cheng's team found that for centuries the strength of the monsoon was associated with natural factors such as solar variation and average Northern Hemisphere temperatures. The timing of major monsoonal shifts coincided with the rise and fall of several Chinese dynasties, implying that these societies' agricultural foundations were at the mercy of changing rainfall. The tables turned, however, at around 1960, say the researchers, when the correlation between the Asian Monsoon and temperature switched.

The authors conclude that from the mid-twentieth century, human-induced climate change has superseded natural variation as the dominant influence on the monsoon.