Clues contained in tree rings have identified mid-14th-century volcanic activity as a potential catalyst for the devastating Black Death in Europe. Researchers from the University of Cambridge and the Leibniz Institute for the History and Culture of Eastern Europe (GWZO) in Leipzig have combined climate data and documentary evidence to present a comprehensive picture of the ‘perfect storm’ that resulted in the deaths of tens of millions and brought profound demographic, economic, political, cultural, and religious changes.
Their findings suggest that a volcanic eruption—or a series of eruptions—around 1345 led to a significant drop in annual temperatures due to the haze from volcanic ash and gases. This climatic shift caused widespread crop failures across the Mediterranean region. In response, Italian city-states leveraged their trade connections to import grain from producers around the Black Sea, inadvertently facilitating the spread of the deadly bacterium that caused the Black Death.
Linking Climate and Catastrophe
This study marks the first instance where high-quality natural and historical proxy data have been used to draw a direct line between climate, agriculture, trade, and the origins of the Black Death. Published in the journal Communications Earth & Environment, the research provides new insights into one of history’s largest disasters. Between 1347 and 1353, the Black Death claimed millions of lives across Europe, with mortality rates reaching up to 60% in some areas.
While it is widely accepted that the disease was caused by the bacterium Yersinia pestis, which originated from wild rodent populations in central Asia and reached Europe via the Black Sea region, the precise timing, location, and rapid spread of the Black Death have remained enigmatic. Professor Ulf Büntgen from Cambridge’s Department of Geography expressed a long-standing interest in understanding the drivers of the Black Death’s onset and transmission.
“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?” – Professor Ulf Büntgen
Reconstructing the Past
Professor Büntgen, whose research group uses tree rings to reconstruct past climate variability, collaborated with Dr. Martin Bauch, a historian of medieval climate and epidemiology from the Leibniz Institute. They examined the period before the Black Death in terms of food security systems and recurring famines to contextualize the situation post-1345. Their goal was to assess the climate, environmental, and economic factors that triggered the second plague pandemic in Europe.
Their research combined high-resolution climate data with documentary evidence, revealing that a volcanic eruption around 1345 likely initiated a sequence of events leading to the Black Death. Tree rings from the Spanish Pyrenees indicated consecutive ‘Blue Rings,’ pointing to unusually cold and wet summers in 1345, 1346, and 1347 across southern Europe. Such consecutive cold summers are rare, and documentary evidence from the same period notes unusual cloudiness and dark lunar eclipses, suggesting volcanic activity.
Trade Routes as a Double-Edged Sword
The resulting climatic downturn led to poor harvests and famine. However, Italian maritime republics like Venice, Genoa, and Pisa managed to import grain from the Mongols of the Golden Horde around the Sea of Azov in 1347, thanks to their established long-distance trade routes. While this averted immediate starvation, it also set the stage for a larger catastrophe.
“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.” – Dr. Martin Bauch
The grain ships from the Black Sea likely carried fleas infected with Yersinia pestis. Once these fleas arrived in Mediterranean ports, they became vectors for disease transmission, allowing the bacterium to jump from rodents to humans, spreading rapidly across Europe.
Lessons from History
Evidence of the Black Death is still visible in many European towns and cities nearly 800 years later. For instance, Corpus Christi College in Cambridge was founded by townspeople after the plague devastated the local community. However, some Italian cities, such as Milan and Rome, were likely spared due to their lack of reliance on imported grain after 1345.
The researchers suggest that the ‘perfect storm’ of climate, agricultural, societal, and economic factors leading to the Black Death can be seen as an early example of globalization’s consequences. The probability of zoonotic diseases emerging under climate change and evolving into pandemics is likely to increase in today’s interconnected world.
“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 globalized world.” – Professor Ulf Büntgen
Resilience to future pandemics, the researchers argue, requires a holistic approach addressing a wide spectrum of health threats. Modern risk assessments should incorporate historical knowledge of the interactions between climate, disease, and society.
The research was supported by the European Research Council, the Czech Science Foundation, and the Volkswagen Foundation, highlighting the importance of interdisciplinary collaboration in understanding historical pandemics and preparing for future health challenges.
