A recent study from Nature Communications Earth and Environment establishes a possible link between volcanic eruption driven climate changes and civilisational collapse of Chinese dynasties from the first two millennia BCE.
The study employed ice core reconstructions as proxies for explosive volcanism, which was a key driver in severe, short-term ecological change. Ice cores from Greenland and Antarctica were assessed for elevated sulphate levels, an indicator of volcanic eruptions, and nearly 156 tropical and extratropical eruptions in the Northern Hemisphere were identified.
These were corroborated by historical (literary and artistic) records. Most studies trying to ascribe a palaeo-climatic agency in social or civilisational collapse are encumbered by the lack of reliable, temporally contextualised, scientific proxies; and instead rely on anecdotal accounts from that day and age.
The two millennia of the Common Era (CE; aka Anna Domini or AD) witnessed the fall of nearly 68 dynasties in China. Upon associating records of volcano explosions and dates of collapses, it was found that 62 out of 68 dynastic collapses were preceded by a volcanic eruption.
Geoscience: Chinese dynastic collapses linked to volcanic eruptions | Communications Earth & Environment | Nature Portfolio: https://t.co/QyUH74XMGo
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While the association might be a mere coincidence, when subjected to statistical scrutiny, the results “confirm a repeated and systematic role for volcanic climate shocks as causal agents in the collapse of successive dynasties” in China, one of the oldest and long-lasting civilisations.
Earlier, the pattern of dynastic rise and fall was attributed to decadence, moral decay, weak rulers and corruption.
Environmental changes have only recently taken the centre stage as a key player in the ‘dynastic cycle.’ In many cases, inclement weather or climate conditions were just seen as a withdrawal of the ‘mandate of heaven,’ that a volcanic eruption was essentially engineered by heaven to punish bad performance.
Other common environmental factors like drought and cold have also been invoked for the collapse of various Chinese dynasties: Tang (907 CE), Yuan (1368 CE) and Ming (1644 CE) dynasty.
There is strong evidence for a volcanic eruption and pre-existing socio-economic stressors acting in concert before the dynasty ultimately kneeled. For instance, volcanic eruptions lead to pronounced summer cooling, as the incoming solar radiation gets scattered by aerosols in the air.
Explosive volcanism has been considered a key driver for external climate forcing in recent climate research as well. A 2015 study, by comparing tree -ring records with mathematical models concluded that two large eruptions in 1257 and 1815 led to an extra tropical summer cooling of 0.8 to 1.3 deg C.
If the eruption happens in the sowing/harvesting season, it can have severe effects such as livestock death and accelerated land degradation. Volcanoes would, thus, have accentuated prevailing vulnerabilities like agricultural failures or fiscal instability or other political/economic factors.
Volcanic eruptions and the sudden abandonment of cities is not something seen only in Chinese history. Pompeii is an oft-cited, classic example: within a few hours of the volcanic eruption of Mt Vesuvius in August, 79 CE, the entire city was covered in volcanic debris and it lasted for centuries. It was not before the 1700s that archaeological excavations uncovered an entire city, with its building and entire population, frozen in time.
Similarly, in 630 CE, the Eastern Turkic Khanate, then the most powerful country in Northeast Asia, suddenly collapsed. A 2006 study argued that a volcanic eruption in 626 CE could have triggered a series of ‘severe disasters of snow and frost’ leading to widespread deaths and famine.
Another indicator of pre-existing vulnerabilities that the authors considered was warfare. Warfare, the researchers acknowledge, could be “a response to and an amplifier of such stress.”
By pulling up reconstructions of warfare events between 850 and 1911 CE, the authors found “an often-marked elevation of warfare in the decades immediately before collapse” as well as an increase in warfare in one or two years immediately after collapse.
However, the authors caution against jumping on causal inferences between volcanic eruptions and ‘collapse’. It is not as if the city always gets abandoned in entirety overnight every time there is an eruption. Some dynasties actually were fairly resilient and continued to survive for nearly ten years after an eruption, while others collapsed quickly.
Chaochao Gao, Associate Professor, Zhejiang University, China, who co-led the research, said in a release: “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 author is a freelance science communicator. (mail[at]ritvikc[dot]com)