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Medieval volcanoes may have ignited the Black Death

Medieval volcanoes may have ignited the Black Death
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    Source: Popular Science
    Category: Science
    Originally Published: 2025-12-04
    Curated: 2025-12-04 16:25

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    While fleas, rats, and global trade played a major role, no single organism or action allowed the bubonic plague (Yersinia pestis) to wreak havoc during the 14th century. Understanding the complex network of preceding events and their consequences is the only way to get a clearer picture of the Black Death’s infamous devastation. Now, researchers say newly analyzed evidence suggests an additional, unexpected reason for the plague’s medieval resurgence.

    Writing in the journal Communications Earth & Environment, a team from the University of Cambridge in the United Kingdom and Germany’s Leibniz Institute for the History and Culture of Eastern Europe (GWZO) say one or multiple volcanic eruptions around 1345 helped usher in the pandemic that ultimately killed 30 to 50 percent of the population across Africa, Central Asia, and Europe.

    “This is something I’ve wanted to understand for a long time,” Ulf BĂŒntgen, a University of Cambridge geographer and study coauthor, said in a statement. “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.”

    Close-up of tree ring samples taken from the Pyrenees, showing ‘blue rings.’ Credit: Ulf BĂŒntgen

    Tree rings tell a story

    To investigate these lingering questions, BĂŒntgen’s team collaborated with GWZO medieval climate and epidemiology historian Martin Bausch to collect high-resolution data and documentary evidence from the years before the Black Death’s arrival. Researchers were particularly interested in examining food security systems and famines during that time to better contextualize what they describe as a “perfect storm” for the plague.

    However, the breakthrough came in the form of a comparatively innocuous dataset: centuries’ old trees in Spanish Pyrenees. Each ring in a tree trunk tells the story of a particular year. Many of the rings hinted at unusually cold and wet summers in 1345 to 1347. A single cooler summer isn’t particularly telling, but it’s far rarer to see multiple consecutive summers with similarly cold temperatures.

    Researchers then corroborated these summers to written primary sources, which noted oddly cloudy skies and dark lunar eclipses. Taken together, the written sources and tree rings imply nearby volcanic activity around 1345. This was further supported by documentary evidence of poorer crop yields, weak harvests, and resultant famines. By 1347, the Italian republics of Genoa, Pisa, and Venice began importing grain from the Mongols living near the Sea of Azov.

    “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,” Bauch explained. “But ultimately, these would inadvertently lead to a far bigger catastrophe.”

    The study’s authors believe that these grain ships arrived with stowaways: plague-infected fleas. Once in Europe, the fleas transferred to rodents and the Black Death began its infamous spread.

    A warning for today

    The effects of the Black Death in Europe famously weren’t uniform. Instead, the plague also tells a story of class, resources, and privilege.

    “In so many European towns and cities you can find some evidence of the Black Death, almost 800 years later
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 BĂŒntgen. “The climate-famine-grain connection has potential for explaining other plague waves.”

    BĂŒntgen added that while such a unique set of cascading effects may sound like a rare occurrence, the chances may be increasing due to climate change .

    “The probability of zoonotic diseases emerging under climate change and translating into pandemics is likely to increase in a globalised world,” he said. “This is especially relevant given our recent experiences with COVID-19.”

    Faster and more effective sustainability strategies remain crucial to staving off the worst effects of the climate crisis and its effect on health. But by better understanding climate-induced crises of the past, researchers like BĂŒntgen and Bauch are helping plan for the future.

    This article was curated from Popular Science. All rights belong to the original publisher.