A volcanic eruption might have helped bring the Black Plague to Europe

An erupting volcano may have kicked off a chain of events that led to the swift dance of the Black Plague across Europe in the 14th century, in a pandemic that killed tens of millions of people.

New analyses of tree ring data, ice cores and historical accounts suggest that a powerful volcanic eruption somewhere in the tropics around 1345 sent clouds of ash around the world, darkening the skies over Europe, researchers report December 4 in Communications Earth & Environment. The ash lingered through several growing seasons, turning Europe’s climate colder and wetter — and that, in turn, caused widespread crop failure across southern Europe and the Mediterranean region. Grain became scarce and prices skyrocketed. Famine gripped the region.

Tragically, the catastrophe didn’t stop there, say climate historian Martin Bauch of the Leibniz Institute for the History and Culture of Eastern Europe in Germany and environmental systems scientist Ulf Büntgen of the University of Cambridge in England.

To ease the burden of starvation, in 1347 many of Italy’s city-states, including Venice and Genoa, decided to import grain from the Mongol-controlled lands around the Black Sea and the Sea of Azov.

That lifesaving grain wasn’t the only cargo the Italian trade ships brought back. A strain of the bacterium Yersinia pestis, which had originated in the steppes of central Asia around 1338, was by 1347 spreading through the wild rodent populations around the Black Sea. And, the researchers note, the routes of the trade ships delivering grain from port to port around the Italian peninsula closely tracks to the region’s first plague outbreaks in 1347.

To understand the climate of the time, the researchers turned to tree rings, finding a rare consecutive series of “blue rings” in trees in the Spanish Pyrenees dating to 1345, 1346 and 1347 Those rings suggest a string of unusually cold, wet summers across southern Europe. Historical accounts from the time recounted incessant cloudiness and especially dark lunar eclipses, observations that scientists have used to help determine the timing of past eruptions.

Although the arrival of the Black Plague via trade shipping might have occurred sooner or later, this chain of events explains how its onset was synchronized across so many different cities so close together, the team says.

It was a perfect storm of geologic, climatic, agricultural, societal and economic factors, they add. And it highlights how globalization has long fostered the spread of pandemics, such as COVID-19.