An unlikely set of clues helps reconstruct ancient Chinese disasters
A few very different clues suggest the cause – or at least one of the causes – of this upheaval: modern weather simulations, archaeological sites hundreds of miles from China’s coast, coastal sediments in Japan and South Korea that record the intensity of ancient typhoons, and even divination texts from the Shang dynasty. These three pieces of evidence converged on the same dates, telling one horrific story.
Reconstructing ancient storm seasons
We have a pretty good idea of how the size and intensity of a storm determines the type of imprint it leaves on coastal sediments. Researchers look for similar traces in ancient sediments and use them to piece together what tropical storm seasons were like in the past (the field is called paleotempestology, which is your trusty correspondent’s new favorite word).
Based on paleotempestological records not only in China but also along the coasts of South Korea and southwest Japan, typhoons moving westward across the Pacific Ocean tended to be more intense during storm seasons around 2,800 years ago. Typhoons that curved north had more intense seasons about 3,800 years ago, and then again about 3,300 years ago.
These more intense typhoon episodes may be linked to something that happened off the coast of Peru about 3,000 years ago, when El Niño events suddenly became more frequent, more extreme and longer lasting. Paleoclimate researchers know this because at this time, shell species that live in cool waters (but cannot tolerate heat) virtually disappear from the Peruvian archaeological record, replaced by more heat-tolerant species. Around the same time, coastal residents gave up building huge monumental temples and villages shrank. You’re going to want to keep these dates in mind, because…
Ding and his colleagues mapped radiocarbon dates from sites in China’s Central Plains and the Chengdu Plain, hoping to identify population shifts and potential signs of a society in crisis. They noticed that the number of sites in the central plain, where the Shang dynasty lived, had declined sharply around 3,800 years ago, and then again around 3,300 years ago; at sites that were not abandoned, changes suggest smaller populations overall. In the Chengdu Plain, something similar happened about 2,800 years ago. Villages, towns and cities moved to higher ground; the layers of mud left by the floods suggest the reason.
