Stalagmite analysis links dynastic collapses to climate change

Chinese dynasties have risen and fallen over the past 2,000 years like solar clockwork, flourishing and declining according to the intensity of the Sun, an academic study by Chinese and American researchers has found.

This cosmic view of Chinese dynasties may sound more like astrological divination than hard research, but the conclusion made the cover story of the journal Science yesterday.

The researchers from Lanzhou University and the University of Minnesota found that as solar activity declined, the Asian monsoon weakened, leading to reduced agricultural production.

The idea is not new. Last year, a team of German scientists found that the collapse of Tang dynasty, one of the golden periods of civilisation, was a result of climate change. The conclusion stirred much controversy in the scientific community, especially on the mainland.

Many scientists suspected the conclusion was too simple and attacked the study, saying the sample used was thought to be faulty and the Germans' data under-analysed.

But the Lanzhou and Minnesota analysts claim to have found robust evidence compiled with unprecedented precision. The key is a stalagmite in a cave that had to meet strict criteria, and was difficult to find.

'The internal structure must be extremely tight, it must live through a major span of Chinese civilisation and it must contain lots of uranium [for dating purposes],' said Zhang Pingzhong , the key author of the study, from Lanzhou University.