Volcano eruption may have led to the Black Death coming to Europe

The Black Death, a bubonic plague outbreak that killed up to 60 per cent of the population of medieval Europe, may have been set in motion by volcanic activity around 1345.

The plague bacterium, Yersinia pestis, is spread by fleas feeding on rodents and then carried to humans bitten by infected fleas. It is unclear what led to the 14th-century outbreak in Europe, but historical sources suggest that the transport of grain from the Black Sea to Italy may have played a role.

“The Black Death is a central event of the Middle Ages and I wanted to understand why such an extraordinary amount of grain had to be brought to Italy specifically in 1347,” says Martin Bauch at the Leibniz Institute for the History and Culture of Eastern Europe in Germany.

To investigate, Bauch and his colleague Ulf Büntgen at the University of Cambridge reviewed evidence about the climate from tree ring data, ice cores and written accounts.

Observers in Japan, China, Germany, France and Italy all independently reported reduced sunshine and increased cloudiness between 1345 and 1349. This was probably the result of a sulphur-rich volcanic eruption – or several eruptions – in an unknown tropical location, Bauch and Büntgen suggest.

Ice cores from Greenland and the Antarctic, along with thousands of tree ring timber samples collected across eight different European regions, also suggest a dramatic climate event may have happened.

What’s more, the researchers found official records showing that, facing famine caused by the cold weather and failing crops, Italian authorities implemented an emergency plan to import grain from the Mongols of the Golden Horde around the Sea of Azov in 1347.

“They acted in a highly professional, rational and efficient manner and achieved their goal to alleviate high prices and impending famine through grain imports before starvation deaths could occur,” says Bauch. “Precisely because these societies practised excellent famine prevention, the plague bacterium arrived in Italy as a stowaway, carried in with the grain.”

At the time, the cause of plague wasn’t known and the outbreak was blamed on things such as “astral constellations and toxic vapours released into the atmosphere by earthquakes”, he says.

While the plague may have reached Europe eventually anyway, perhaps the population losses would have been smaller if this emergency response hadn’t occurred, says Bauch. “My argument is not against preparedness, but rather for an awareness that effective precautionary measures in one sphere can create problems in unexpected areas.”

Aparna Lal at the Australian National University in Canberra says it is likely that “a perfect storm of factors” led to the Black Death entering Europe. “Rising food prices, the widespread famine documented, together with the cold, wet weather, may have resulted in reduced immunity due to inadequate nutrition, and induced behaviour change such as spending more time indoors near others for extended periods,” she says.

However, more work will be required to untangle causation from correlation, she says. “The short-term perturbations caused by the eruptions appear to have had considerable impact on local weather patterns as documented, but whether they were the cause of the Black Death entering Europe, as stated, requires more evidence,” says Lal.

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