Volcanic eruptions may have contributed to the collapse of dynasties in China, a new study has found. Photo courtesy of the U.S. Geological Survey
Nov. 11 (UPI) -- Volcanic eruptions helped collapse dynasties in China in the last 2,000 years by temporarily cooling the climate and affecting agriculture, a study published Thursday by Communications Earth & Environment found.
Large eruptions created a cloud that blocked some sunlight for a year or two, reducing the warming of land in Asia in the summer and leading to weaker monsoons and less rainfall, the data showed.
This, in turn, led to decreases in crop harvests, causing hunger and migration that were factors in the collapse of several ruling dynasties in the region, the researchers said.
"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," co-author Alan Robock said in a press release.
"The impact of a cooled climate on crops can also make conflict more likely, further increasing the probability of collapse," said Robock, a professor of environmental sciences at Rutgers University in New Brunswick, New Jersey.
Erupting volcanoes can pump millions of tons of sulfur dioxide into the upper atmosphere, forming vast sulfuric acid clouds that reflect sunlight and lower the Earth's average surface temperature.
Major eruptions can lead to "a double jeopardy of marked coldness and dryness during the agricultural growing season," the researchers said.
These impacts may be worsened by livestock deaths, accelerated land degradation and more crop damage from agricultural pests that survive during milder winters.
For this study, Robock and his colleagues reconstructed 156 explosive volcanic eruptions from 1 A.D. to 1915 by examining elevated sulfate levels in ice cores from Greenland and Antarctic.
They also analyzed historical documents on 68 Chinese dynasties and examined warfare in the region between 850 and 1911.
Smaller volcanic "shocks" to the climate may have caused dynasties to collapse when political and socioeconomic stress is already high, the data showed.
In addition, larger shocks may have led to collapses, even without other factors such as poor leadership, administrative corruption and demographic pressures.
The findings 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, the researchers said.
Future volcanic eruptions could also impact countries with a history of resource mismanagement, such as in Syria before the 2011 uprising, which may have been partly triggered by drought.
When combined with climate change, these eruptions are also likely to profoundly affect agriculture in some of the Earth's most populous and most marginalized regions, the researchers said.
Eruptions during the 20th and 21st centuries have been smaller than many during imperial China, but have still contributed to the Sahelian drought of the 1970s to 1990s, resulting in about 250,000 deaths and 10 million refugees in this economically marginalized region, they said.
"The relationship is complex," Robock said.
"If there is ongoing warfare and conflict, dynasties are more susceptible to collapse," he said.