A dramatic headline begins the piece: volcanic eruptions may have lit the fuse for Europe’s Black Death. New research traces the chain of events from climate shocks to catastrophe, using both tree-ring data and historical records to craft the most complete picture yet of how the plague unfolded. Proponents from the University of Cambridge and the Leibniz Institute for the History and Culture of Eastern Europe (GWZO) combine climate reconstructions with documentary evidence to explain a sequence that culminated in tens of millions of deaths and sparked profound shifts across society.
The study, published in Communications Earth & Environment (https://doi.org/10.1038/s43247-025-02964-0), suggests that a volcanic eruption—or a series of eruptions—around 1345 cooled European skies for several years. The resulting ash and gases dimmed sunlight, depressed temperatures, and ravaged crops throughout the Mediterranean. In response to the threat of riots and famine, Italian city-states leveraged well-established grain trade routes with Black Sea producers to secure food supplies.
For more than a century, these maritime powers had built a robust, globe-spanning trade network that helped prevent hunger. Yet this very system helped seed a far greater disaster. The climate-driven disruption of long-distance commerce reduced famine risk in the short term but also transported Yersinia pestis—the bacterium behind the plague—on grain ships, seeding the first and deadliest wave of the second plague pandemic into Europe. This represents the first direct synthesis of high-resolution natural and historical proxies linking climate, agriculture, trade, and the plague’s origins.
The Black Death stands as one of humanity’s most devastating episodes. Between 1347 and 1353, millions died across Europe, with mortality rates reaching as high as about 60% in some regions. Although it is widely accepted that Yersinia pestis originated in wild rodent populations in Central Asia and reached Europe via the Black Sea, researchers continue to debate why the outbreak began precisely when and where it did, why its impact was so catastrophic, and how its spread accelerated so rapidly. As Professor Ulf Büntgen of Cambridge’s Department of Geography notes, understanding the drivers of onset and transmission—and their rarity—has long been a guiding question in the field.
Büntgen’s team specializes in reconstructing past climate from tree rings, collaborating with Dr. Martin Bauch, a medieval climate and epidemiology historian at the GWZO. Bauch explains that examining the pre-1345 era’s food-security framework and recurring famines is essential for contextualizing the post-1345 period. The goal was to integrate climate, environmental, and economic perspectives to illuminate what triggered the European second plague pandemic.
By fusing high-resolution climate data with documentary sources and fresh interpretations of human-environment links, the researchers argue that a volcanic eruption in 1345—or a cluster of eruptions—likely initiated a chain of events leading to the Black Death.
Evidence from the Spanish Pyrenees—specifically a streak of unusually cold and wet summers labeled as consecutive “Blue Rings”—points to 1345–1347 as a period of exceptional climatic downturn across southern Europe. While a single cold year can occur, back-to-back cold summers are unusual. Contemporary accounts also describe cloudiness and dark lunar eclipses, reinforcing the volcanic signal. The resulting harvest failures and famines spurred drastic social and economic responses. Yet the Italian maritime republics—Venice, Genoa, and Pisa—managed to import grain from the Mongol-controlled Golden Horde around the Sea of Azov in 1347, revealing how longstanding trade networks could both avert hunger and unintentionally accelerate a catastrophe. Bauch emphasizes that this is precisely how a climate-driven food crisis can become a pandemic vector through trade.
The ships carrying grain likely bore fleas infected with Yersinia pestis, a mechanism supported by prior discoveries. Although the exact origin of the bacterium remains debated, ancient DNA points to possible reservoirs in wild gerbils across Central Asia.
When plague-bearing fleas reached 14th-century Mediterranean ports via these grain shipments, they transmitted the pathogen from rodent hosts to humans, rapidly spreading across the continent. Büntgen notes that countless towns and cities still bear traces of the Black Death’s impact nearly eight centuries later, with examples such as Corpus Christi College in Cambridge rising from communities devastated by the outbreak. Similar legacies appear across Europe.
The researchers also caution that climate-driven emergence of zoonotic diseases—and their potential to become pandemics—could become more common in a highly connected world.
Büntgen adds that some major Italian cities, including Milan and Rome, likely escaped the worst effects because their grain needs diminished after 1345, underscoring how regional differences in resilience shaped the trajectory of the plague. This climate–famine–trade linkage may illuminate other waves of plague as well.
Looking ahead, the team argues that responding to future pandemics requires a holistic approach that considers the full spectrum of climate, agriculture, and societal factors. Modern risk assessments should learn from history’s lessons about how environmental shocks and global networks interact to shape health outcomes.
Funding for the study came from the European Research Council, the Czech Science Foundation, and the Volkswagen Foundation. Source: University of Cambridge (07.12.2025).
