When a volcano erupts, clouds of ash may spew into the atmosphere and block the effects of the sunlight for more than a year. Volcano eruptions can also release millions of tons of sulfur dioxide into the upper atmosphere, forming vast sulfuric acid clouds that reflect sunlight and lower Earth’s average surface temperature. These environmental extremes can affect the growth of plants, as well as the survival of animals and humans alike.
In a new study by scientists at Rutgers University-New Brunswick, the fall of ruling dynasties in China has been associated with past major eruptions in volcanoes. In order to investigate this relationship, the scientists reconstructed 156 explosive volcanic eruptions between 1 A.D. and 1915 by identifying layers with elevated sufate levels in ice cores from Greenland and the Antarctic. The researchers also analyzed historical documents relating to 68 Chinese dynasties that ruled between 850 and 1911, and the warfare that took place during each dynasty’s rule.
“We confirmed for the first time that collapses of dynasties in China over the last 2,000 years are more likely in the years after volcanic eruptions,” said study co-author Professor Alan Robock. “But the relationship is complex because if there is ongoing warfare and conflict, dynasties are more susceptible to collapse. The impact of a cooled climate on crops can also make conflict more likely, further increasing the probability of collapse.”
The researchers found that major volcanic eruptions could lead to “a double jeopardy of marked coldness and dryness during the agricultural growing season.” This would have led to crop failures and famines, which could have been made worse by associated livestock deaths, accelerated land degradation and more crop damage from agricultural pests that could survive during the milder winters.
Smaller volcanic eruptions may also have caused dynasties to collapse, particularly when political and socioeconomic stress was already high. Larger eruptions may have led to collapses without substantial pre-existing stress. Other factors that could have been involved in the collapse of dynasties include poor leadership, administrative corruption and demographic pressures.
The scientists emphasize the need to prepare for future eruptions, especially in regions with economically vulnerable populations (perhaps comparable to the Ming and Tang dynasties in China) or that have a history of resource mismanagement, as in Syria before the 2011 uprising that may have been partly triggered by drought.
Although volcanic eruptions have been smaller during the 20th and 21st centuries than they were during the time of imperial China, they can still cause significant disruption to ecosystems and populations. Moderate eruptions may have contributed to the Sahelian drought of the 1970s to 1990s, which led to about 250,000 deaths and resulted in 10 million refugees in this economically marginalized region.
Future major eruptions, combined with climate change, are likely to have profound effects on agriculture and food security in some of the Earth’s most populous and marginalized regions, the study says.
The research is published in the journal Communications Earth & Environment.