Via CDT, an interesting piece that argues the Tang dynasty may have been done in by climate change. (The full report can be found in the journal Nature, but is available to subscribers only.)
According to a collaborative effort between scientists from Germany and China, between 700 and 900 CE the climate changed, the winter monsoon was strong but the summer monsoons weakened. This period was also marked by cooler temperatures and shorter growing seasons.
What eventually brought down the dynasty were the prolonged droughts, which caused significant crops failures and subsequent peasant uprisings. This ultimately led to the collapse of the dynasty in 907. The team led by Gerald Haug of the Geoforschungszentrum (GFZ) in Potsdam, eastern Germany, suggests that this shift in tropical precipitation occurred on both sides of the Pacific, and not just in coastal East Asia. The same migration of the rainband occurred in Central America and doomed the so-called classic period of the Mayan civilisation, at almost exactly the same time as the Tang era, they state in this week’s Nature. Comparisons of the titanium records from the Huguangyan Lake, in Guangdong province, and from the Cariaco basin, in Venezuela, have thrown up remarkable