A volcanic eruption may have catalyzed the plague’s arrival in Europe, study suggests

When the Black Death struck Europe beginning in 1347, the plague wiped out more than half of the continent’s population, upending societies and halting wars.

New research suggests that one or more volcanic eruptions, unknown to Europe’s residents, most likely catalyzed the pandemic’s arrival on the continent’s shores.

The theory, outlined in a study published Thursday in the journal Communications Earth & Environment, suggests that the eruptions triggered a series of events that allowed the fleas that spread the plague to proliferate in Europe.

The eruptions lowered global temperatures for a few years, causing a sudden climate change that affected crops in Europe. Facing poor harvests and growing fears of famine, some wealthy Italian city-states like Florence and Venice imported grain from elsewhere in the world. And on these ships were most likely fleas infected with the plague.

The actions of Florence’s leaders averted a mass famine: tens of thousands of famine refugees emigrated there and the city was able to feed them in addition to its own citizens. But the imports unwittingly sparked a pandemic.

The city’s leaders were proud that they had managed to provide enough food for so many people, said Martin Bauch, author of the new study and a medieval historian at the Leibniz Institute for Eastern European History and Culture in Germany.

“They couldn’t have had any idea of ​​the danger that existed there,” he said.

The research offers a historic example of how climate change can alter human societies and animal ecosystems in ways that are difficult to predict and with incredible downstream consequences.

Researchers have debated and sought details about the origin and spread of plague for decades, but this study is the first to describe in detail the potential role of a volcanic eruption. Previous research has suggested that climate change may be responsible for the introduction of plague at different times in history, but most studies have been vague on this, according to Henry Fell, a postdoctoral researcher at the University of Nottingham and the University of York in England.

“I think this paper is really useful because it’s very specific about the mechanism behind it,” said Fell, who was not involved in the study but has studied the Black Death and climate change. “We are seeing an increase in grain trade from these ports, and the cause is climate. »

Volcanic eruptions can cool the planet by injecting sulfur into the stratosphere, reducing the amount of sunlight that can reach the Earth’s surface.

“It literally blocks some of the sun, which leads to cooling,” Fell said.

The effect can last for several years after significant breakouts.

To understand 14th century volcanic activity for the new study, researchers examined tree ring records, ice core data and written historical observations. All three lines of evidence agreed: a period of cooling and a Mediterranean famine from 1345 to 1347 preceded and coincided with the emergence of the plague in Europe.

The team studied the chemical composition of ice cores in Greenland and Antarctica, because ice layers in polar regions can trap chemicals from falling snow, providing a timeline of sorts. They found that the year 1345 had the 18th strongest sulfur signal in the last 2,000 years. The amount of material injected into the stratosphere that year exceeded the best recent example of this dynamic, the Mount Pinatubo injection in 1991.

Meanwhile, tree rings from the same period show biological spots called “blue rings” that indicate stress and a likely cold snap. Blue rings appear consecutively, which is extremely rare.

Finally, written accounts from the time in China, Japan, Germany, France and Italy today report less sunshine and increased cloudiness, according to the study.

Researchers couldn’t identify the particular volcano or volcanoes that erupted in 1345. But they did determine the region of the world: “It must have been a tropical eruption,” Bauch said.

The reason: Ice cores from Earth’s two poles contained roughly equal amounts of volcanic sulfate.

Historical records document poor harvests and high wheat prices during this cool period, with severe famine across much of Spain, southern France, Italy, Egypt and the eastern Mediterranean, according to the new study.

At the time, Italian city-states were wealthy, Bauch said, and had developed grain storage systems and huge trade networks established over centuries.

But as the famine worsened, their options dwindled.

“They really start to realize in 1347, ‘We have to import from the Black Sea. This is the last place where they still have enough grain for our needs,'” Bauch said.

“Of course, they don’t know how the plague reaches them,” he added. “I have records from Venice in 1349, and they’re really happy, and they say, ‘Look, in the last famine, grain from the Black Sea really saved us, and it worked really well.'”

Bauch said he suspected the plague would likely have eventually reached Europe, but that events triggered by volcanic eruptions would likely have accelerated the process.

Up to 60% of the population died in parts of Europe between 1347 and 1353, making it one of the deadliest periods in history.

Previous research into the origins of the plague has relied on written accounts, archaeological evidence and even genetic clues. In 2022, scientists found DNA evidence of the bacteria that causes the plague in bodies buried in what is now Kyrgyzstan, in the far east of Europe. Gravestones indicate that many of those killed were buried in 1338 and 1339 (about a decade before the plague hit Europe) and that they died of the “plague.”

The same research group also found that marmots living today in the Tian Shan mountain range near the burial site carry a closely related strain of the bacteria, indicating that the Black Death may have originated there before spreading elsewhere.

The new study could explain what happened next, Fell said, adding that he thought the authors had made a compelling argument that a volcano was to blame.

After the plague first exploded in Europe, it reappeared for centuries, reshaping human history.

“In the European context, this is very important to our history,” Fell said. “Any study covering a long period across Europe will be a scourge.”

This article was originally published on NBCNews.com