The volcanic eruption that may have unleashed the deadly Black Death plague on Europe

Eight people wearing white robes and pointed hats walk barefoot in procession behind a group of three men dressed in colorful clothing. Men carry flags. — photo caption, The Black Death radically changed medieval society.

- author, Helen Briggs
- Author title, BBC environment correspondent
December 4, 2025

A volcanic eruption around 1345 may have set off a chain reaction that caused Europe’s deadliest pandemic, the Black Death, according to scientists.

Evidence preserved in tree rings suggests that the eruption caused dramatic climate change and triggered a chain of events that brought disease to medieval Europe.

According to this hypothesis, ash and gases from the volcanic eruption caused a severe drop in temperatures and led to crop failure.

To avoid famine, Italy’s densely populated cities were forced to import grain from areas around the Black Sea, bringing with them plague-carrying fleas that also carried the disease to Europe.

Map titled "How did the Black Death spread across Europe?"Which indicates the transmission of the disease through the grain trade network. The map covers Europe, the Mediterranean, and the Black Sea. Major ports are marked: red dots for export ports (e.g. Tana, Alexandria), blue dots for import ports (e.g. Oslo, Messina) and orange dots for trade centers (e.g. Venice, Genoa, Pisa, Crete). Dashed black arrows indicate the direction of the plague's spread: starting at Tana on the Black Sea, moving southwest to Constantinople and Crete, then west to Messina in Sicily, north to Pisa and Genoa, then north to Venice. From Italy, the routes extend northwest to France and then north to Oslo. Another route extends from Alexandria in Egypt to the island of Crete and then integrates into the Mediterranean trade network. There is a small inset map highlighting the area within Europe. Source: University of Cambridge.

This “perfect storm” of climate impact, famine and trade reminds us how diseases can emerge and spread in a globalized, warming world, according to experts.

“Although the co-occurrence of factors that contributed to the Black Death appears rare, the likelihood of zoonotic diseases emerging from climate change and becoming pandemics is likely to increase in a globalized world,” said Ulf Böntgen of the University of Cambridge in England.

“This is especially important given our recent experiences with Covid-19,” he added.

A stunted tree with short, bare branches stands between rocks in a barren, rocky valley under a bright blue sky. — photo caption, Tree rings from the Spanish Pyrenees indicate unusually cold summers in 1345, 1346, and 1347.

The Black Death devastated Europe between 1348 and 1349, killing half the population.

The cause of the disease was a bacteria known as Yersinia pestis– It is transmitted by wild rodents, such as mice and fleas.

The outbreak is believed to have begun in Central Asia and spread around the world through trade.

The exact sequence of events that brought the disease to Europe, where millions of people died, has been the subject of exhaustive study by science.

Now, researchers from the University of Cambridge and the Leibniz Institute for Eastern European History and Culture (GWZO) in Leipzig, Germany, have completed a key piece of this puzzle.

They used information from tree rings and ice cores to study climate conditions around the time of the Black Death.

Their evidence suggests that volcanic activity around 1345 caused temperatures to drop sharply for several years in a row due to the release of volcanic ash and gases that blocked some of the sun’s rays.

This in turn led to crop failure throughout the Mediterranean region.

To avoid famine, Italian city-states traded with grain producers from the Black Sea region, unwittingly allowing deadly bacteria to establish themselves in Europe.

The small, wingless insect that feeds on blood has a red color on a purple background. — photo caption, Fleas transmit plague from infected mice to humans.

Martin Bausch, a historian specializing in medieval climate and epidemiology at the GWZO, said the climate events coincided with a “complex system of food security”, creating a “perfect storm”.

“For more than a century, these powerful Italian city-states established long-distance trade routes across the Mediterranean and the Black Sea, which allowed them to activate a highly efficient famine prevention system,” he explained.

“But this will ultimately inadvertently lead to a much greater disaster.”

These results were published in the scientific journal Earth and Environment Communications.

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