Ash spewing from a volcano may have been the trigger that brought the Black Death to Europe in the 14th century, new research says. This pandemic-scale plague killed tens of millions of people.
Scientists studied tree-ring data, ice cores and historical accounts. In these, they found signs of a powerful volcanic eruption in the tropics around 1345. It spewed clouds of ash around the world, darkening Europe’s skies. This cooled the climate and fostered rain.
Those effects lingered through several growing seasons, it now appears. Widespread crop failures in Southern Europe made grain scarce and costly. Hunger soon gripped the Mediterranean region.
This famine triggered a catastrophic chain of events, researchers now report. Climate historian Martin Bauch works at the Leibniz Institute for the History and Culture of Eastern Europe. That’s in Germany. Ulf Büntgen is an environmental systems scientist at the University of Cambridge in England. The two shared their new analysis Dec. 4, 2025, in Communications Earth & Environment.
A plague of converging factors
To ease starvation, in 1347 some city-states in Italy decided to import grain. Grown in central Asia, such as Kyrgyzstan, this grain was brought back from Asian ports on the Black Sea and the Sea of Azov.
But grain wasn’t the only cargo these ships brought home. As early as 1338, the bacterium Yersinia pestis had been spreading through wild rodents near the Black Sea. This infectious microbe causes the black plague (PLAYG).
Bauch and Büntgen traced routes those ancient trading ships had taken. They had brought grain from where the first plague outbreaks had showed up in 1347.
Then the researchers turned to tree rings to understand the climate back then. They found a rare series of “blue rings” in trees from the Spanish Pyrenees. These rings dated to 1345, 1346 and 1347. They point to three straight years of cold, wet summers.
Written accounts from that time also note constant cloudiness and dark lunar eclipses. Such observations help scientists pin down the timing of ancient volcanic eruptions.
The plague likely would have arrived in Europe via ships at some point. But this chain of events now seems to explain why its onset occurred so close in time in so many cities, the team says.
The plague behind the Black Death was due to a mix of geologic, climatic, farming, societal and income issues, Bauch and Büntgen believe. It highlights how — long before COVID-19 — global trade has played a big role in the spread of some pandemics.
