Climate makes history, a study proves once again: When the Chinese imperial dynasties fell in the last 2,000 years, the consequences of volcanic eruptions apparently often played a role. An interdisciplinary team of researchers was able to prove this statistically by combining data from ice cores and historical information. However, complex interactions also became clear: if the political systems were already unstable, the dynasties were particularly sensitive to the critical developments resulting from the volcanic climate effects, the researchers report.
Droughts, floods or devastating storms: it is well known that climatic capers and their consequences, such as crop failures, can have a significant impact on the lives of millions of people and damage the economy. This, in turn, can lead to societal explosives that destabilize political systems. There are numerous examples of this from history – including recent ones: It is assumed, for example, that repeated droughts played a role in the developments in Syria that led to the refugee crisis. Such developments could now occur more frequently in the wake of climate change, so a fear.
In addition to these long-term risks, special events can also cause climatic capers: volcanic eruptions. Violent eruptions can release clouds of sulfuric acid into the atmosphere, blocking some of the sunlight for a year or two. The consequences can be complex and far-reaching changes in the climate – such as heavy rainfall in certain regions and droughts in others. In this context, researchers have previously shown possible connections between volcanic eruptions and certain historical developments. In the current case, an international team has dealt with the possible effects of volcanic eruptions on the course of the long history of the Chinese Empire. It is known that volcanic eruptions in the northern hemisphere in Asia can lead, among other things, to cold summers in the north and a weaker monsoon and thus less precipitation in the south. Both effects have the potential to trigger significant crop failures.
Patterns emerge
For the study, the interdisciplinary research team first reconstructed a total of 156 explosive volcanic eruptions from 1 AD to 1915. The results are based on the analysis of ice cores from Greenland and the Antarctic, in which they were able to detect and date volcanically increased sulfur concentrations. They then compared this data with historical information on 68 Chinese dynasties over the past 2,000 years. “China has a remarkably long and well-documented history,” says co-author Francis Ludlow of Trinity College Dublin. “Since there were so many precisely dated political collapses, we could not just look at individual cases, but many at the same time to see if there was a repeating pattern associated with volcanic eruptions,” said the scientist.
At first it became clear that 62 of the 68 dynastic collapses were preceded by at least one volcanic eruption. “We were able to show for the first time that in China after volcanic eruptions it was much more likely that dynasties would collapse. There is a system behind this, ”says co-author Michael Sigl from the University of Bern. The researchers were able to make this clear through their statistical analyzes: “Our calculations show that the probability that eruptions preceded so many dynastic collapses only by chance is only 0.05 percent,” says co-author John Matthews of Trinity College.
Factors in a complex system
The researchers emphasize, however, that the consequences of volcanic eruptions cannot be defined as the sole cause of political collapse – they always represent an aspect in a complex system of interactions. Some dynasties also showed themselves to be comparatively resistant to the consequences of volcanic eruptions. It is becoming apparent that the level of political and socio-economic pressure already in place played an important role. Factors included, for example, the quality of leadership, the spread of corruption, demographic pressure and armed conflicts.
“We found that even a small volcanic eruption could help trigger a collapse if the pre-existing instability was high. However, larger eruptions could cause a collapse even if the instability was comparatively small beforehand, ”says Matthews. “As always, the historical context is the key to understanding how the climate can affect a society”.
The scientists are thus directing their gaze to the present: According to them, the combination of man-made climate change with the ever-possible volcanic eruptions could be particularly problematic today. “It is clear that we should prepare for the next big eruption”. Matthews emphasizes: “So far, the volcanic eruptions that we have experienced in the twentieth and twenty-first centuries were minor compared to those with which the Chinese imperial dynasties had to deal,” says the scientist. Co-author Chaochao Gao from Zhejiang University in China concludes: “This study shows us the importance of building a resilient society in order to cope with the natural hazards we are exposed to – be they volcanic or volcanic not.”
Source: Trinity College Dublin, University of Bern, specialist article: Commun Earth Environ, doi: 10.1038 / s43247-021-00284-7