Zhejiang University: Scientists explore the role of volcanic-induced climate stress on societal collapses

A comprehensive assessment of the influence of climate on past societal changes is key to understanding human vulnerability to present and future climate change. However, few studies have advanced beyond qualitative associations and often indulge in environmentally deterministic or overly simple monocausal explanations. Even where links can be convincingly argued in individual cases, such as between an abrupt change in climate and the collapse or fall of a civilization, major questions remain regarding how systematic the role of climate has been throughout human history.

Prof. GAO Chaochao from the Zhejiang University College of Environmental and Resource Sciences, and Prof. Francis Ludlow from School of Histories & Humanities, Trinity College Dublin led a study to systematically explore the role that abrupt climate stress, induced by explosive volcanism, may have played on the Chinese dynastic collapse throughout the Common Era. The results are presented in a research paper titled “Volcanic Climate Impacts Can Act as Ultimate and Proximate Causes of Chinese Dynastic Collapse”, which is published in Communications Earth & Environment and highlighted in Nature on Nov.11th.

The relative role of climatic versus internal human stressors in societal collapse remains persistently controversial across the many disciplines that engage with this question. A significant source of uncertainty is the chronological accuracy and precision of the evidence underlying both proposed collapses and potential climatic influences.

To address this, the study established the consensus collapse dates of 68 Chinese dynasties by surveying 58 major works of history and employed Nature’s landmark 2015 multi-ice-core reconstruction of explosive volcanism that corrected long-standing errors in previous ice-core-based eruption dates. Combining these two long and chronologically precise series for the first time reveals a repeated association between the dates of explosive volcanism and Chinese dynastic collapse, highly statistically significant at >99% confidence, across the past two millennia.

Large eruptions can create an aerosol cloud that can block incoming sunlight for a year or two, cooling the land in Asia in the summer and leading to a weaker monsoon, reducing crop harvests and causing agroecological and socioeconomic disruption. But volcanic climatic impacts do not act alone. “We wanted to understand how a sudden climate change caused by a major eruption might interact with other existing stressors experienced by a dynasty”, said Ludlow.

This study thus took warfare, richly documented in Chinese historical sources, as a proxy for broader socioeconomic and political stress, and revealed a key dynamic in which volcanically induced climate shocks could act along a spectrum of causality. This ranged from small to moderate eruptions that could act as the ultimate cause of a collapse if societal stresses were already high, while larger eruptions had the potential to act more independently as proximate causes even when pre-existing societal stresses were low.

The severity of societal impact from a volcanically induced climatic shock, including the probability of a political collapse, was thus heavily mediated by the historical context in which eruptions occurred. “There is no simplistic environmentally deterministic story here,” said Ludlow, “but it is also clearly a mistake to ignore climatic forces in explaining the history of these powerful and sophisticated dynasties.”

“People today could not see the ancient moon, the moon once shone on the ancient people”, as lamented by LI Bai – one of the greatest Chinese poets of all times (701-762 CE). Ice core records have told us the history of past volcanism, and now in this study we can see the societal influence of these eruptions. But we can also see that despite the strong link between eruptions and collapses, there were many large eruptions that were not followed by a collapse, suggesting the frequent resilience of past dynasties. This shows us both the complexity of the human-nature system and the possibility that we can also build a society resilient to and prepared for future climatic hazards,” said Gao.

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