Researchers from the University of Cambridge and the Leibniz Institute for the History and Culture of Eastern Europe (GWZO) in Leipzig have provided new insights into the origins of the Black Death, linking a series of volcanic eruptions to one of history’s deadliest pandemics. Their study, published in Communications Earth & Environment, combines climate data with historical records to trace how environmental events set off a chain reaction that led to tens of millions of deaths across Europe.
The research suggests that around 1345, a major volcanic eruption or cluster of eruptions released ash and gases into the atmosphere, causing annual temperatures to drop for several years. This cooling led to widespread crop failures throughout the Mediterranean region. In response, Italian city-states turned to their established trade routes with grain producers near the Black Sea to secure food supplies and prevent famine.
While this shift in trade helped avoid starvation, it also had unintended consequences. The ships transporting grain also carried fleas infected with Yersinia pestis, the bacterium responsible for the Black Death. This facilitated the entry and rapid spread of plague across Europe.
“This is something I’ve wanted to understand for a long time,” said Professor Ulf Büntgen from Cambridge’s Department of Geography. “What were the drivers of the onset and transmission of the Black Death, and how unusual were they? Why did it happen at this exact time and place in European history? It’s such an interesting question, but it’s one no one can answer alone.”
Büntgen collaborated with Dr Martin Bauch from GWZO on this interdisciplinary project. “We looked into the period before the Black Death with regard to food security systems and recurring famines, which was important to put the situation after 1345 in context,” said Bauch. “We wanted to look at the climate, environmental and economic factors together, so we could more fully understand what triggered the onset of the second plague pandemic in Europe.”
Their analysis drew on tree ring data from Spain’s Pyrenees mountains—where consecutive ‘Blue Rings’ indicate cold summers between 1345 and 1347—and written accounts describing unusual cloudiness and dark lunar eclipses during that period as further evidence for volcanic activity.
“For more than a century, these powerful Italian city-states had established long-distance trade routes across the Mediterranean and the Black Sea, allowing them to activate a highly efficient system to prevent starvation,” said Bauch. “But ultimately, these would inadvertently lead to a far bigger catastrophe.”
Although previous studies identified ships as carriers for plague-infected fleas entering Mediterranean ports via grain shipments, this new research clarifies why there was such urgent demand for imported grain at that specific time.
Once arrived in port cities during those years following 1345, infected fleas found new hosts among rodents—and potentially domesticated animals—enabling Yersinia pestis transmission to humans. The disease then spread rapidly throughout Europe.
“And yet, we could also demonstrate that many Italian cities, even large ones like Milan and Rome, were most probably not affected by the Black Death, apparently because they did not need to import grain after 1345,” said Bauch. “The climate-famine-grain connection has potential for explaining other plague waves.”
The researchers argue that this sequence represents an early example of globalisation’s risks: interconnected societies facing health threats amplified by environmental changes.
“Although the coincidence of factors that contributed to the Black Death seems rare, the probability of zoonotic diseases emerging under climate change and translating into pandemics is likely to increase in a globalised world,” said Büntgen. “This is especially relevant given our recent experiences with Covid-19.”
They recommend modern risk assessments draw lessons from history by considering interactions between climate change, disease emergence and societal responses when preparing for future pandemics.
The study received support from several organizations including The European Research Council (ERC), Czech Science Foundation (GAČR), and Volkswagen Foundation.