The demise of some of China's ruling dynasties may have been linked to changes in the strength of monsoon rains, a new study suggests.
The findings come from 1,800-year record of the Asian monsoon preserved in a stalagmite from a Chinese cave.
Weak - and therefore dry - monsoon periods coincided with the demise of the Tang, Yuan and Ming imperial dynasties, the scientists said.
A US-Chinese team report their work in the journal Science.
Stalagmites are largely made up of calcium carbonate, which precipitates from groundwater dripping from the ceiling of a cave.
Chemical analysis of a 118mm-long stalagmite from Wangxiang Cave, in Gansu province, north-west China, told the history of strong and weak cycles in the monsoon - the rains that water crops to feed millions of people in Asia.
It also shows that, over the last 50 years, greenhouse gases and aerosols have taken over from natural variability to become ...