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A previously unknown volcanic eruption may have set off a chain reaction that ultimately brought the Black Death to medieval Europe, killing tens of millions in what became humanity's most devastating pandemic, according to new research published Thursday.
The study, which analyzed tree rings from Spain's Pyrenees mountains, suggests that volcanic activity in 1345 cooled the climate across southern Europe, destroying harvests and forcing Italian merchants to import grain from central Asia on ships that unknowingly carried plague-infected rodents.
The findings offer a fresh perspective on how the bubonic plague outbreak reached Europe and spread with such catastrophic speed during the mid-14th century, wiping out up to 60 percent of the population in some regions.
Researchers established through tree ring analysis that southern Europe experienced unusually cold and wet summers from 1345 to 1347. By cross-referencing this climate data with historical written accounts, they determined that temperatures likely dropped due to reduced sunlight following one or more volcanic eruptions in 1345.
The abrupt climate shift devastated agricultural production across the region, ruining harvests and creating the conditions for widespread famine. Tree ring analysis, which examines growth patterns in wood to reconstruct past environmental conditions, has become an increasingly valuable tool for understanding historical climate fluctuations.
Italian city-states including Venice, Genoa and Pisa had established extensive Mediterranean and Black Sea trade networks that initially appeared to offer salvation from starvation. Martin Bauch, a historian at Germany's Leibniz Institute for the History and Culture of Eastern Europe, noted that these "powerful Italian city states had established long-distance trade routes across the Mediterranean and the Black Sea, allowing them to activate a highly efficient system to prevent starvation."
However, Bauch added, these same commercial lifelines "would inadvertently lead to a far bigger catastrophe."
The merchant vessels brought grain from the Mongol Golden Horde in central Asia, where researchers believe the plague first emerged. Previous studies have indicated these ships carried unwanted passengers: rats harboring fleas infected with Yersinia pestis, the bacterium responsible for plague.
Between 25 and 50 million people died over the following six years as the disease swept through Europe. While the pandemic resulted from a confluence of natural, demographic, economic and political factors, the researchers argue that the volcanic eruption served as the critical initial trigger for the disaster.
Study co-author Ulf Buentgen of Cambridge University in the UK drew connections to contemporary concerns, stating that "the probability of zoonotic diseases emerging under climate change and translating into pandemics is likely to increase in a globalised world." He added, "This is especially relevant given our recent experiences with Covid-19."
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