The history of imperial China stretches back at least 4,000 years, from the legendary Xia dynasty established by Yu the Great. Numerous dynasties followed the Xia, claiming a “mandate of heaven” after periods of warfare. Researchers in China, Europe, and the United States, however, have found that volcanic eruptions (as well as conflict) may have contributed to dynastic collapse because they cooled the climate and affected agricultural production.
Not Just Coincidence
Cooler land temperatures caused by sunlight-blocking clouds of sulfuric acid can weaken monsoon rains, cutting crop yields. In a study published in Communications Earth and Environment, the researchers described how they analyzed ice cores to compare evidence of explosive volcanic activity with events in Chinese history. They determined that dynastic collapse was more likely in the years following volcanic eruptions, but the effect was especially pronounced with preexisting conflict.
“These results for the first time confirm a repeated and systematic role for volcanic climatic shocks as causal agents in the collapse of successive dynasties in one of the world’s most populous and long-lasting civilizations, using the most complete and robust list of collapse dates yet compiled,” they wrote.
The finding may sound counterintuitive because China has had few volcanoes active in recent history. Most of the volcanoes in the period studied were not active in China itself, however, researchers believed. Instead, they said that volcanic activity in Indonesia and the Philippines significantly affected temperature and rainfall in China.
Study coauthor Chaochao Gao, an associate professor in the Department of Environmental Science at Zhejiang University in China, realized that many dynastic changes had happened around the time of big eruptions, so she and her collaborators set out to see whether there was a link.
To unravel any relationship between volcanism and political events, they examined ice cores from sites in Greenland and Antarctica and looked for spikes in sulfur levels relative to background levels; the more sulfate, the greater the potential for a larger climate impact. Aided by work on a new ice chronology by coauthor Michael Sigl of the University of Bern’s Physics Institute, they teased out 158 eruptions from 1 CE to 1915, a few years after the fall of the Qing dynasty (China’s last), and found a pattern.
“In some of our previous and ongoing studies, we found that severe drought or flood, frost damage, locust and plague outbreaks occurred in the posteruption years,” said Gao. “We also found significant influence of volcanic eruptions on ENSO [El Niño–Southern Oscillation] variations, which feed back to modulate monsoon climate, which is essential for Chinese agriculture. Other studies had established links between severe weather generally and major societal stresses in China, and some had even connected specific volcanic eruptions to specific cases of dynastic collapse, such as the eruption of Mount Parker in the Philippines in 1641 and the collapse of the great Ming dynasty in 1644, though the eruption certainly didn’t act alone.”
Social Unrest and Climate Change
One challenge in the research was grappling with the question of why some major volcanic events, such as the massive 1815 eruption of Mount Tambora in Indonesia, did not correspond to dynastic change, whereas more moderate events (when combined with warfare) did.
“What we found was that collapses could follow small to moderate eruptions when instability was already high,” said coauthor Francis Ludlow, an associate professor of history at Trinity College Dublin. “In this case you might think of the volcanic climatic shock acting as the ultimate cause of collapse. More or less as a final nail in the coffin. But larger eruptions might precede collapse even when preexisting instability was low. This suggested that these events could have enough of an impact to be thought of as more fundamental proximate causes of collapse.”
“I believe that explosive volcanism might occur at any time, including [during] the flourishing age of a dynasty,” said Fan Ka Wai, an associate professor in the Department of Chinese and History at City University of Hong Kong who was not involved in the study. “I do not believe that each explosive volcano would have an impact on the fall of a dynasty.”
China’s dynasties may be long gone, but the team’s findings are relevant today in that they come at a time of both increasing social unrest and climate change.
“In the 20th and (so far) 21st centuries, we have been lucky to avoid facing eruptions of the size faced by many Chinese dynasties over the past 2 millennia,” said Ludlow. “But the next big one can happen at any time, and we are also likely to be increasing the probability of extreme weather from anthropogenic climate change. How much chronic socioeconomic instability and inequality we wish to tolerate will strongly influence the level of impact these events will have. Ultimately, it is up to us to determine how prepared we wish to be.”
—Tim Hornyak (@robotopia), Science Writer