Volcanic eruptions may have triggered abrupt climate changes contributing to the repeated collapse of Chinese dynasties over the past 2,000 years, according to new research.
The study, published in Communications Earth & Environment, illustrates how volcanic eruptions can profoundly impact vulnerable or unstable regions and highlights the need to prepare for future eruptions. The researchers combined historical evidence with polar ice-core records of 156 volcanic eruptions, which date from 1 A.D. to 1915. This exercise found that 62 of the 68 dynastic collapses were closely preceded by at least one volcanic eruption.
Large eruptions create a cloud that blocks some sunlight for a year or two. That reduces warming of the land in Asia in the summer and leads to a weaker monsoon and less rainfall, reducing crop harvests and causing livestock death.
“China has a remarkably long and richly documented history of multiple ruling dynasties, including major world powers like the Tang Dynasty, which collapsed in 907 CE, or the Ming Dynasty, which collapsed in 1644,” explains Francis Ludlow, Associate Professor of Medieval Environmental History at Trinity, who jointly led the study. “With so many precisely dated collapses, we can look not just at individual cases of collapse that may or may not have followed a change in climate, but rather look simultaneously at many collapses to see whether there is a repeated pattern where a change in climate was followed by collapse. This can tell us whether climatic change played a very minor role in dynastic collapse, or whether it posed a systematic threat to these powerful and sophisticated societies.”
Major eruptions can lead to “a double jeopardy of marked coldness and dryness during the agricultural growing season,” the study says. Impacts may be worsened by livestock deaths, accelerated land degradation and more crop damage from agricultural pests that survive during milder winters.
Scientists found that smaller volcanic “shocks” to the climate may cause dynasties to collapse when political and socioeconomic stress is already high. Larger shocks may lead to collapses without substantial pre-existing stress. Other factors include poor leadership, administrative corruption and demographic pressures.
“Mandate of heaven,” an influential Chinese concept, allowed for some continuity between dynasties. Elites and “commoners” more readily accepted a new dynasty that, by seizing power, demonstrated a divine mandate to rule that the former dynasty had lost.
“Researchers have identified a lot of historical eruptions through sulphate deposits in the polar ice, so we expect that some collapses will have been preceded by eruptions purely by chance,” adds John Matthews, postdoctoral fellow at the Trinity Centre for Environmental Humanities and co-author on the paper. “To convince ourselves we were seeing something significant, we ran the numbers and found there would be just a 0.05% chance of seeing so many collapses preceded by so many eruptions if that had actually happened randomly. This study shows a repeated link between volcanic eruptions and dynastic collapse.”
Some dynasties, the authors note, withstood numerous large eruptions before eventually succumbing, suggesting that the role of volcanism in collapse is far from straightforward and that dynasties were often resilient to sudden, volcanically triggered, climate shocks.
To gain further insight, the researchers assessed the role of explosive volcanism in tandem with other sources of stress or instability that a dynasty might experience by examining levels of warfare prevailing in the decades before collapse. Warfare was found to be elevated before most collapses, but the study also revealed a strong link between the magnitude of a volcanic climatic shock and the level of pre-existing stress.
“We found that even a small volcanic eruption might help trigger a collapse when pre-existing instability was high,” the researchers explain. “Larger eruptions, however, could trigger a collapse even when pre-existing instability was minimal. So as ever, historical context is key to understanding how climate can impact a society. It is also clear that we should be preparing for the impacts of the next big eruption – so far in the twentieth and twenty-first centuries, the eruptions we’ve experienced have been minnows compared to some that these dynasties had to deal with.”
Along with researchers from Trinity College Dublin, Rutgers University and Zhejiang University in China. Chaochao Gao, an Associate Professor at Zhejiang University, China, concludes, “This study tells us how important it is to build a resilient society to cope with the natural hazards that we face, be they volcanically-induced or otherwise.”
The article, “Volcanic climate impacts can act as ultimate and proximate causes of Chinese dynastic collapse,” by Chaochao Gao, Francis Ludlow, John A. Matthews, Alexander R. Stine, Alan Robock, Yuqing Pan, Richard Breen, Brianán Nolan and Michael Sigl, is published in Communications Earth & Environment. Click here to read it.
Top Image:Detail of China and East Asia from a 1763 Chinese map of the world – Wikimedia Commons