The Black Death May Be Linked to a Mysterious Volcanic Eruption

How a neglected eruption could have triggered the Black Death

By Meghan Bartels edited by Andrea Thompson

The infamous Black Death – a pandemic that killed between a third and half of Europeans in just a few years – may have been aided in its devastation by an unknown volcanic eruption.

This is the hypothesis presented in research published on December 4 in Earth and Environment Communicationswhich claims the eruption triggered several seasons of climate instability and poor harvests. This instability, in turn, forced several Italian states to import grain reserves from new sources, particularly from regions surrounding the Black Sea. According to the researchers, on these grain granaries there were fleas infected with Yersinia pestisthe bacteria responsible for the plague.

Martin Bauch, a medieval and environmental historian at the Leibniz Institute for Eastern European History and Culture in Germany, studies the historical famine. Looking through historical records, he noticed a particularly severe crop failure beginning in northwest Italy in late 1345 after severe rainstorms. In just two years, the Black Death had begun, so he was curious if there might be a connection.

On supporting science journalism

If you enjoy this article, please consider supporting our award-winning journalism by subscription. By purchasing a subscription, you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

Analysis of grain trade records suggests that some Italian cities exhausted their usual food supplies, forcing them to import grain from the Black Sea region. Although this measure helped feed people, it may have introduced the Black Death to Europe as a nightmare, Bauch and his co-author suggest.

Researchers analyzed tree ring data from across Europe to see how temperatures fluctuated in the century before the Black Death to better understand the massive rains that Bauch had seen referenced in records. Then they consulted other scientists’ studies of polar ice cores, looking for signs of volcanic eruptions that injected high-altitude sulfur into the atmosphere, where they can affect climates far from the volcano itself, including changes in precipitation patterns. Here a powerful eruption stood out in 1345.

The eruption itself remains mysterious. Researchers suspect it happened relatively close to the equator because its debris is visible in the ice sheets at both poles. But it will take significant additional work to identify the culprit. “No one considers this eruption particularly interesting,” says Bauch. “We hope that will change.”

Historians once thought the plague was carried to Italy by sailors fleeing a battle in the east, but that theory has collapsed in recent years. Meanwhile, researchers have found growing evidence that the disease was circulating in Asia in the decades before the Black Death began, setting the stage for the pandemic. “None of this could have happened without a lot of other things happening before,” says Monica Green, a medical historian who works extensively on the plague and the Black Death and who was not involved in the new research.

Even without a particular outbreak having been identified, the new research offers a refreshingly specific hypothesis, says Henry Fell, a disease ecologist who studies plague at the University of Nottingham and the University of York in England, who was not involved in the new research. “Climate is regularly cited as a driver of the Black Death; however, it is relatively difficult to determine what mechanism links climate to the plague,” he says. Indeed, plague is a complex disease system, in which people, bacteria, fleas, and multiple species of rodents all interact across time and space.

Although researchers of all stripes have spent centuries understanding the causes of the Black Death, the new study highlights that this research is not yet complete. And it remains vital even today, both as plague continues to circulate in pockets of the globe and as COVID reminds us of the price of pandemics.

“We need to understand pandemics better,” Green says. “It’s sort of a moral imperative.”

It’s time to defend science

If you enjoyed this article, I would like to ask for your support. Scientific American has been defending science and industry for 180 years, and we are currently experiencing perhaps the most critical moment in these two centuries of history.

I was a Scientific American subscriber since the age of 12, and it helped shape the way I see the world. SciAm always educates and delights me, and inspires a sense of respect for our vast and magnificent universe. I hope this is the case for you too.

If you subscribe to Scientific Americanyou help ensure our coverage centers on meaningful research and discoveries; that we have the resources to account for decisions that threaten laboratories across the United States; and that we support budding and working scientists at a time when the value of science itself too often goes unrecognized.

In exchange, you receive essential information, captivating podcasts, brilliant infographics, newsletters not to be missed, unmissable videos, stimulating games and the best writings and reports from the scientific world. You can even offer a subscription to someone.

There has never been a more important time for us to stand up and show why science matters. I hope you will support us in this mission.