A study links a volcanic eruption around 1345 to climate disruptions that prompted Italy to import plague-carrying grain from the Black Sea region in 1347. This emergency measure, aimed at averting famine, likely introduced the bacterium Yersinia pestis to Europe, fueling the Black Death pandemic. Researchers analyzed tree rings, ice cores, and historical records to support this connection.
The Black Death, which devastated medieval Europe by killing up to 60 percent of its population, originated from the bacterium Yersinia pestis. Transmitted via fleas on rodents to humans, the plague's 14th-century outbreak in Europe remains partly mysterious. Historical accounts point to grain shipments from the Black Sea to Italy as a key vector.
Martin Bauch from the Leibniz Institute for the History and Culture of Eastern Europe in Germany sought to explain the massive grain imports to Italy in 1347. Collaborating with Ulf Büntgen at the University of Cambridge, they examined climate data from tree rings, ice cores, and contemporary writings. Between 1345 and 1349, observers in Japan, China, Germany, France, and Italy noted reduced sunlight and greater cloud cover, indicative of a sulphur-rich volcanic eruption—or multiple—in an unidentified tropical area.
Supporting evidence includes ice cores from Greenland and Antarctica, plus tree ring samples from eight European regions, signaling a major climate shift. This led to cold, wet conditions causing crop failures and famine in Italy. In response, officials efficiently imported grain from the Mongols of the Golden Horde near the Sea of Azov.
"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," Bauch explained. However, this success inadvertently carried the plague bacterium as a stowaway in the grain. At the time, the disease was attributed to factors like astral influences or earthquake-released toxic vapors.
Bauch cautions that while the plague might have reached Europe regardless, the rapid imports amplified the disaster. "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 from the Australian National University agrees a "perfect storm" of elements—rising food prices, famine, poor nutrition weakening immunity, and indoor crowding—likely facilitated the outbreak. Yet she stresses the need for further research to distinguish cause from correlation, noting the eruptions' short-term weather impacts but questioning direct causation for the plague's entry.
The findings appear in Communications Earth & Environment (DOI: 10.1038/s43247-025-02964-0).