A group of Norwegian and Swiss researchers have uncovered links between climatic changes in central Asia and repeated outbreaks of the Bubonic plague in Europe, starting with the Black Death in the 14th century.
In an article published this week in the Proceedings of the National Academy of Sciences, the researchers examined tree ring records throughout Europe and Asia, and found 16 instances, ranging between the 14th and 19th centuries, where periods of warm springs and wet summers would corresponded with an upsurge in plague in Europe about 15 years later.
Our findings support a scenario where climate fluctuations that positively affect tree-ring growth in the juniper trees in the Karakorum mountain range [in the border region of China, India and Pakistan] also affect climate in a larger region in a way that can promote and synchronize plague outbreaks among the rodent populations of Central Asia. When the climate subsequently becomes unfavorable, it facilitates the collapse of plague-infected rodent populations forcing their fleas to find alternative hosts. Such large-scale wildlife plague outbreaks in Asia would, during the time of the second plague pandemic, frequently result in the arrival of plague to Europe harbors.
They add that the plague could have spread by trade caravans that crisscrossed Asia along the Silk Road – infecting people or camels, or perhaps with the fleas finding a home in the cargo. This challenges the idea that the plague bacterium Yersinia pestis sustained itself among the wildlife in Europe, especially the black rat.
The researchers, who come from Oslo University and the Swiss Federal Research Institute WSL, note that the ultimate confirmation of this hypothesis depends on the availability of appropriate genetic material of ancient plague victims not only from different periods throughout time but also from different parts of Eurasia. The advent of aDNA techniques and international research collaboration across disciplinary boundaries will most likely be able to shed new light on this fascinating topic at the interface of human history and environmental variability.