The Black Death’s horrifying spread across the 14th century has long been linked to rats, fleas and the webs of global trade that ferried disease between continents. But historians and climate scientists now say the devastating pandemic may have been set in motion by a force far more dramatic: volcanic eruptions.
A new study published in Communications Earth & Environment by researchers from the University of Cambridge and Germany’s Leibniz Institute for the History and Culture of Eastern Europe (GWZO) argues that one or several major eruptions around 1345 likely triggered a series of environmental shocks that helped pave the way for the bubonic plague. The pandemic went on to kill between 30 and 50 per cent of people across Africa, Central Asia and Europe.
“This is something I’ve wanted to understand for a long time,” says Ulf Büntgen, geographer at the University of Cambridge and co-author of the study. “What exactly set the Black Death in motion? Why did it emerge at that particular moment in European history? These are big questions, ones no single field can answer alone.”
Story continues below this ad
Ancient trees reveal a climate clue
To investigate, Büntgen and GWZO historian Martin Bauch collected high-resolution historical and environmental data from the years leading up to the plague. They aimed to understand the food systems, shortages and crises that built what they describe as a medieval “perfect storm”.
The crucial evidence, however, came from an unexpected source: tree rings found in the Spanish Pyrenees. These centuries-old trees recorded unusually cold, wet summers between 1345 and 1347. While a single cool year could be coincidental, multiple consecutive summers of abnormal conditions are rare and often linked to volcanic activity.
Story continues below this ad
The team cross-checked these findings with historical accounts. Medieval writings described murky skies and strangely dark lunar eclipses, signs that align with volcanic aerosols. Crop records from the same period showed poor harvests and widespread shortages. By 1347, major Italian maritime republics such as Venice, Genoa and Pisa were importing grain from Mongol territories around the Sea of Azov.
“For more than a century, these city states had perfected long-distance trade routes across the Mediterranean and Black Sea to prevent famine,” Bauch explains. “But those same supply lines may have set the stage for something far more catastrophic.”
According to the study, the grain ships likely carried infected fleas, silent passengers that unleashed the plague across Europe. Once ashore, the fleas spread to rodents, accelerating the Black Death’s deadly march.
Story continues below this ad
Uneven impacts and modern parallels
The plague’s toll varied sharply from region to region. It was shaped not only by biology, but by class, access to resources and the ability of cities to withstand food shortages.
“In so many European towns and cities, signs of the Black Death still linger almost 800 years later,” Büntgen says. “But we also found evidence that some large Italian cities, Milan and Rome among them, likely escaped the worst of it because they didn’t need to import grain after 1345.”
The researchers say this “climate-famine-grain” connection may help explain the timing of other plague outbreaks throughout history.
Story continues below this ad
Büntgen warns that while the 14th-century cascade of events may seem extraordinary, conditions that promote emerging infectious diseases are increasingly common in a warming world.
“With climate change, the probability of zoonotic diseases emerging and developing into pandemics is likely to rise, especially in a globalised society,” he notes. “Our experience with COVID-19 underscores that risk.”
Understanding these ancient, climate-driven crises, the researchers argue, is essential for planning. Faster, more effective sustainability and public-health strategies will be critical to reducing the kinds of cascading failures that once helped unleash one of the deadliest pandemics in human history.
