How a Volcanic Eruption May Have Sparked the Black Death

A multidisciplinary team of researchers argues that a volcanic eruption around 1345 triggered multi-year cooling that damaged Mediterranean harvests and helped set in motion the chain of events leading to the Black Death. The study, published in Communications Earth & Environment, combines tree-ring records, ice-core chemistry and contemporary documentary evidence to reconstruct a linked climate–trade–disease sequence.

Evidence: Tree Rings and Ice Cores

Environmental scientist Ulf Büntgen analysed thousands of tree-ring samples from living and subfossil wood across Europe. The rings show a pronounced climatic downturn — two to three consecutive years of colder-than-normal conditions — consistent with crop failures in the mid-1340s. Independent ice-core chemical records from both Antarctica and Greenland reveal synchronous sulfur spikes that point to a large, sulfur-rich volcanic eruption, likely in the tropics, around 1345.

Documentary and Historical Evidence

Historian Martin Bauch compiled administrative records, letters, poems, plague treatises and inscriptions that document severe food shortages and unusual social strain in the two years before the plague outbreaks. Those records suggest that Mediterranean grain supplies were stressed enough to prompt emergency imports.

Proposed Mechanism: From Volcano To Plague

The researchers propose this sequence: a large volcanic eruption injected sulfur aerosols into the stratosphere, causing several years of summer cooling; cooler, darker summers reduced Mediterranean harvests and created grain shortfalls; maritime city-states such as Venice and Genoa imported emergency grain from the Black Sea; and those shipments likely carried Yersinia pestis — the plague bacterium — transported on rat fleas and grain dust, introducing the pathogen into busy port cities and enabling rapid urban spread.

“Rat fleas are drawn to grain stores and can survive for months on grain dust as an emergency food source, enabling them to endure long voyages,” said study coauthor Martin Bauch, a historian of medieval climate and epidemiology at the Leibniz Institute for the History and Culture of Eastern Europe.

Geographic Differences and Uncertainties

The volcanic hypothesis may help explain the uneven geographic impact of the Black Death. Cities such as Rome and Milan experienced less severe outbreaks, possibly because they relied more on nearby grain-producing areas and did not depend on imported Black Sea grain as urgently as major maritime hubs.

Important uncertainties remain: the exact location and number of volcanic sources are unknown, and causation cannot be proven definitively more than six centuries later. The paper frames the eruption as a plausible “first domino” in a cascade of environmental, economic and epidemiological factors.

Peer Response and Implications

Independent experts praised the study’s interdisciplinary approach. Mark Welford, head of geography at the University of Northern Iowa, noted the work strengthens understanding of how climate change and disease dynamics can intersect. Mark Bailey (University of East Anglia) and Alex Brown (Durham University) highlighted the study’s sensible emphasis on a rare coincidence of natural and social forces and its value for both historical inquiry and modern pandemic preparedness.

Conclusion

By linking tree-ring cooling, ice-core sulfur spikes and documentary accounts of famine-driven trade, the study offers a compelling hypothesis: a mid-14th-century volcanic eruption helped set off food shortages that rerouted grain trade and unintentionally transported infected fleas into Mediterranean ports, contributing to the outbreak of the Black Death. Whether the eruption was the decisive trigger or one of several contributing factors, the research underscores how climate extremes can amplify disease risk and reshape societies.

Publication: Communications Earth & Environment. Key Authors: Martin Bauch and Ulf Büntgen. Estimated Death Toll: At least 25 million people in Europe between 1347 and 1351; global population before the pandemic was below 450 million.