Ash from the explosion may have led to crop failure and famine in southern Europe, leading some Italian cities to import grain—which possibly carried fleas infected with the bubonic plague

Sara Hashemi - Daily Correspondent

December 8, 2025 10:08 a.m.

The Black Death may have killed more than half of Europe’s population within just a few years. Trionfo della Morte, attributed to Buonamico Buffalmacco, photographed in Pisa by Martin Bauch

An erupting volcano may have spurred the deadliest pandemic known in human history: the Black Death.

Historical records from nature and written texts hint that a volcanic explosion around 1345—about two years before the bubonic plague began ravaging Europe—set in motion a devastating series of events, according to a study published December 4 in the journal Communications Earth & Environment. The findings could help explain the longstanding puzzle of when and how the pathogen behind the Black Death got to the continent.

The proposed chain of events begins with spewed volcanic ash blocking sunlight over the Mediterranean region for several years, leading to a drop in temperatures. That caused crops to fail and famine to spread across the area. So, some Italian cities imported grain from the Black Sea region, northeast of the Mediterranean, which also may have brought fleas with the plague-causing bacterium, *Yersinia pestis. *

“The plague bacterium infects rat fleas, which seek out their preferred hosts—rats and other rodents. Once these hosts have died from the disease, the fleas turn to alternative mammals, including humans,” says study co-author Martin Bauch, a historian of medieval climate and epidemiology at the Leibniz Institute for the History and Culture of Eastern Europe in Germany, to Jacopo Prisco at CNN.

“Rat fleas are drawn to grain stores and can survive for months on grain dust as an emergency food source, enabling them to endure the long voyage from the Black Sea to Italy,” he tells the outlet. Once the grain arrived in port cities, it was placed in central granaries and doled out. The rest, of course, is history.

As the bubonic plague spread across the continent, it may have killed up to 60 percent of Europe’s population between roughly 1347 and 1353.

Did you know? Beyond Europe

While Europe is known as one of the hardest places hit by the Black Death, the disease also decimated populations in the Middle East and North Africa. Researchers assume it struck China and India, too. The bubonic plague still exists today, although cases are rare and it can be treated with antibiotics.

Study co-author Ulf Büntgen, a tree ring researcher at the University of Cambridge in England, first found clues of mid-14th century volcanic activity while studying trees in the Pyrenees mountains in Spain, per Science’s Andrew Curry. Their rings, which collect snapshots of climate conditions that can be dated to specific years, suggested the trees had suffered from the cold during the two summers before the Black Death started to decimate Europe’s population.

In all, tree ring data from eight sites around the continent suggested abnormally frigid, wet summers across the Mediterranean in 1345, 1346 and 1347. The findings made sense with written reports of harvest failures and heavy rain at the time, which forced the Italian republics of Venice, Genoa and Pisa to import grain from the Black Sea region. Moreover, volcanic sulfur found in ice collected in Antarctica and Greenland, which also contains time-specific climate records, suggests a tropical volcano exploded around 1345.

The Dark and Deadly History of the Plague

“These results make the Black Death seem like even more of an anomaly,” Timothy Newfield, a historical epidemiologist at Georgetown University who was not involved in the work, tells Science. “It really demonstrates how many variables had to line up for the Black Death to start.”

But questions remain about the mysterious volcanic eruption that may have sparked Europe’s pandemic. The researchers’ ice analysis suggests that the phenomenon happened close to the equator, but Bauch tells Meghan Bartels at Scientific American more work is required to figure out which volcano is responsible for the climate downturn. “Nobody considers this eruption particularly interesting,” Bauch says to the outlet. “We hope that changes.”

The study illuminates how climate change and globalization can work hand in hand to fuel pandemics.

“We have to have a better understanding of pandemics,” says Monica Green, a historian of medicine at the University of Pittsburgh who was not involved in the study, to* *Scientific American. “That’s kind of the moral imperative.”

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