Climate patterns from cave mineral deposits linked to Chinese dynasty collapses

China’s dynastic history spans 13 periods of rule from 2070 BC until the last emperor abdicated in 1912. While factors leading to the transitions between dynasties are a complex mixture of environmental, social and economic issues, the role of climate change has often been invoked as a significant factor in these geopolitical shifts. This is because China’s reliance upon agriculture prior to the industrial era means the country was sensitive to abrupt changes in climate that could lead to a variety of social and economic impacts.

New research, published in Quaternary Science Reviews, has focused on the role changing precipitation patterns may have played, particularly in regards to variability in Asian monsoons. These natural phenomena result in cold, dry winters leading to drought, and warm, wet summers that see heavy rain between May and September, with tropical cyclones making landfall and wreaking destruction.

To investigate this, Dr. Haowen Fan of China University of Geosciences and colleagues analyzed speleothem records from Heshang Cave in central China that span 2,000 years. These mineral deposits form in caves, accumulating as calcium leaches from groundwater, and are more commonly known as stalactites (growing down from the cave ceiling) and stalagmites (growing up from the cave floor).

Within these speleothems, annual growth bands are present as distinct layers, from which oxygen isotopes (δ¹⁸O) were measured as a proxy for monsoon precipitation through time. For example, during the period 1–400 CE, δ¹⁸O was depleted in the speleothem and coincided with the Roman Warm Period with more precipitation, while the following 400–800 CE experienced increased δ¹⁸O and corresponds to the Dark Age Cold Period with less precipitation.

The research team found that when Asian monsoons are in their positive phase (when sea surface temperatures are higher in the western Indian Ocean and cooler to the east, and therefore, precipitation is higher to the west but lower to the east), these periods often coincided with transitions of China’s dynasties on multidecadal timescales (peak cycles at 13, 35 and 75 years). Notably, the prolonged droughts in Eastern China reduced grain harvests, which caused issues with food sustainability and economic decline.

Significantly, Dr. Fan notes that the variability in climate patterns across China leading to civil unrest is an important finding rather than a universal change throughout the country. Over 80% of China’s population has lived in Eastern China since 221 BC, forming the core territory of the Han, Tang, Northern Song, Yuan, Ming and Qing Dynasties among others, making this region highly susceptible to the consequences of climate change on socio-economics.

For example, the Wei, Jin and North-South Dynasties (181–540 CE) and Tang Dynasty (618–907 CE) occurred during colder periods when monsoons were weaker, while the Ming and Qing Dynasties (1321–1920) prevailed during comparatively warmer conditions when monsoon intensity was stronger. The weakest recorded monsoon occurred 1500–1650 CE and matches the time of the Ming Dynasty collapse, when conditions deteriorated through the Little Ice Age and grain yields declined 20%–50% per capita due to droughts, leading to uprisings that overthrew the dynasty.

Linking monsoon phases to droughts and these water shortages impacting ancient agricultural practices is a fascinating insight into how reduced food supplies may have led to famine, economic downturn and civil unrest that ultimately changed the course of China’s history.

© 2024 Science X Network