Volcanic eruptions could have facilitated the spread of the Black Death

In 1347, the Black Death reached southern Europe, rapidly sweeping across the Italian peninsula and claiming up to half of the population in some regions. Contemporary accounts describe entire households being wiped out, mass graves being dug, and widespread panic engulfing cities. While the Yersinia pestis bacteria and its transmission via rats and fleas have been extensively studied, a new investigation suggests that volcanic eruptions may have played a key role in the diseases rapid expansion.

The plague, which likely emerged in human populations in the early 1300s and devastated Central Asia during the 1330s, did not reach the Mediterranean until 1347. A recent study published in Communications Earth & Environment links the timing of the Black Deaths arrival in Italy with volcanic events that cooled the climate, triggered famine, and prompted extensive grain imports that may have inadvertently carried the disease.

A combination of factors had to align for this to happen. Remove any one of them, and the pandemic may not have occurred, explains historian Hannah Barker from Arizona State University. The outbreak was fueled by an interplay of climate shifts, animal vectors, and human decisions, allowing the Black Death to spread at speeds exceeding a mile per day.

Evidence from Tree Rings and Ice Cores

Geographer Ulf Bntgen of the University of Cambridge uncovered clues linking climate to the pandemic through a study of tree-ring records, which help reconstruct temperature and precipitation over the past two millennia. He found that Mediterranean temperatures were slightly below average from 1345 to 1357. Investigating further, Bntgen collaborated with ice-core specialists and identified elevated sulfur levels in Greenland and Antarctic cores, indicating one or more volcanic eruptions around 1345, likely in the tropics.

Historical Clues and Societal Impact

Bntgen partnered with medieval historian Martin Bauch, who found corroborating hints in historical records. Observers in China and Bohemia reported unusual lunar eclipses, potentially caused by volcanic particles in the atmosphere. The resulting years of cooler climate likely reduced crop yields, prompting Mediterranean city-states to secure food through long-distance trade networks.

During 13461347, grain prices surged as cities like Venice and Genoa imported wheat from North Africa and the Black Sea to avoid famine. Previously, trade conflicts with the Mongols had blocked grain shipments. As plague reduced the Mongol population and Italian cities faced shortages, the trade resumed, inadvertently bringing Yersinia pestis via grain shipments. Fleas carrying the pathogen could survive on grain dust as well as on rats and mice aboard trading vessels.

While these measures helped prevent starvation, they also facilitated the plagues arrival in Italian cities. Imported grain was sent to Padua and Trento, likely sparking outbreaks there. By the end of 1348, the Black Death had struck much of Italy and the Mediterranean.

Connecting Climate and Disease

Previous research had linked grain trade to plague spread, but the volcanic influence was a new discovery. Historian Timothy Newfield notes that the study demonstrates the value of collaboration between historians and climate scientists, providing deeper insights into historical pandemics. Combining historical records with paleoclimatic data offers a clearer understanding of the environmental and societal factors driving disease transmission.

Although modern medicine has drastically reduced deaths from Yersinia pestis, studying the Black Death remains valuable. The pandemic illustrates how rare alignments of climate events, human activity, and animal vectors can produce catastrophic disease outbreaks. Such historical case studies help researchers anticipate and understand the complex interactions between climate and health in both the past and present.

Author: Caleb Jennings