A massive mid-14th-century volcanic eruption likely triggered the spread of the "Black Death"

By Hugo Francisco de SouzaReviewed by Susha Cheriyedath, M.Sc.Dec 9 2025

New interdisciplinary evidence shows how a mid-14th-century volcanic cooling reshaped Mediterranean food security, redirected grain ships from the Black Sea, and inadvertently opened the door to one of history’s deadliest pandemics.

Study: Climate-driven changes in Mediterranean grain trade mitigated famine but introduced the Black Death to medieval Europe. Image Credit: Steve Allen / Shutterstock

In a recent study published in the journal Communications Earth & Environment, researchers argue for a likely causal chain between a sudden climate downturn and the onset of the Black Death.

The study combined paleoclimatic data with historical records to present evidence that a large, unidentified volcanic eruption or cluster of eruptions around 1345 CE triggered a prolonged period of unusually cold conditions accompanied by pronounced regional hydroclimatic variability in southern Europe, leading to widespread agricultural dearth and, in some regions, famine.

To mitigate starvation, Italian maritime republics imported grain from the Black Sea region, a response embedded within sophisticated food security institutions that the authors propose most likely facilitated the transport of plague-infected fleas into the heart of the Mediterranean. 

The study thus highlights how environmental shocks and globalized trade networks can converge to facilitate the rapid spread of pandemics.

Historical Uncertainty Around Black Death Origins

The "Black Death" is the name given to the first wave of the second plague pandemic that spread through Europe between 1347 and 1353 CE. It remains one of the most devastating human disasters in history, claiming up to 60 percent of the European human population at the time (more than 50 million people).

While it is scientifically accepted that the causative bacterium, Yersinia pestis, originated in rodent populations in Central Asia and traveled into Europe via the Black Sea, the specific mechanisms regarding the timing and virulence of its arrival have long been debated.

Previous research has sought to determine whether the disease spreads primarily through human-to-human contact, rodent-to-human contact, or through goods, but with limited success. 

Furthermore, while the mid-14th century is well known for its social instability, the role of climatic changes in facilitating the pandemic has remained a subject of controversy among natural and social scientists.

Integrating Paleoclimate Reconstructions With Medieval Records

The present study aims to bridge these knowledge gaps by leveraging a rigorous interdisciplinary methodology that connects paleoclimatology with historical analysis.

To conduct the climate reconstruction, the study analyzed high-resolution estimates of volcanic stratospheric sulfur injection (VSSI) derived from geochemical analyses of ice cores from Antarctica and Greenland.

Maximum Latewood Density (MXD) measurements from tree rings collected across eight European regions, including the Alps, Scandinavia, and the Pyrenees, were subsequently analyzed to estimate local temperature impacts, specifically, summer temperature anomalies that might have altered pandemic dispersal patterns during the 1347–53 seasons within a broader Northern Hemisphere extratropical climate context.

For the historical analysis, previously analyzed climatic data were cross-referenced with a vast array of narrative and administrative sources from 1344 to 1348 CE. Study data included:

• Grain prices, Wheat and millet price reconstructions from Italy, Catalonia, and the Middle East

• Policy measures, Administrative records detailing grain export bans, forced loans, and import premiums in Italian city-states such as Venice and Genoa

• Grape harvests and records of wine yields in northwestern Italy served as an additional proxy for agricultural productivity.

Volcanic Cooling and Agricultural Crisis in the 1340s

The results from the multidisciplinary analyses suggest that a sequence of natural disasters, particularly volcanic eruptions, likely played a key role in driving the trade movements for the transport of grain that imported the plague.

Ice core data revealed a large, unidentified tropical volcanic eruption, or a cluster of eruptions, around 1345 CE. This event was estimated to have injected approximately 14 teragrams (Tg) of sulfur into the stratosphere, substantially more than the 6 Tg released by the eruption of Mount Pinatubo in 1991. This eruption likely triggered a period of sharp cooling across the Northern Hemisphere extratropics, with especially strong impacts in the Mediterranean.

Tree-ring analysis validated this hypothesis by identifying 1345, 1346, and 1347 CE as the coldest consecutive summers in the Northern Hemisphere extratropics since 1257. In the Pyrenees, the cold was so severe that it caused "Blue Rings", a rare wood anatomical feature indicating a lack of cell-wall lignification due to freezing temperatures during the growing season.

Climate-Driven Grain Shortages and Trade Realignments

The study proposes that this cold, spatially heterogeneous climate led to catastrophic harvest failures. Wheat prices in 1347 CE were documented as reaching their highest levels in eight decades.

In response, Venice and Genoa reportedly lifted trade embargoes and sourced grain from the territories of the Golden Horde around the Sea of Azov. Pandemic records from the period finally reveal a synchronization between grain deliveries and disease. Venetian ships, carrying grain that may plausibly have been infested with Y. pestis-carrying fleas, returned from the Black Sea in late 1347.

The first documented cases of plague in Venice are reported to have appeared less than two months after these ships arrived. Conversely, cities like Milan and Rome, which did not rely on Black Sea grain imports during this specific crisis, were spared the initial wave of the Black Death outbreak. 

The authors note, however, that alternative mechanisms, such as multiple reintroductions or other transmission pathways, remain possible and require further investigation.

Interplay of Climate Shocks and Trade Networks in Pandemic Spread

The present study presents the first multidisciplinary evidence aimed at addressing the role of climate change and stochastic events that facilitated the unprecedented dispersal and virulence of the Black Death.

Study results identified the onset of the Black Death not as a random biological event, but as the result of a "unique spatiotemporal coincidence" of natural and societal factors. The sophisticated conventional Italian food security system, designed to provide resilience against dearth, paradoxically served as the gateway for the pandemic. 

The authors further emphasize broader implications, noting that in an increasingly interconnected and warming world, climate shocks interacting with globalized trade networks are likely to raise the probability that zoonotic pathogens cross ecological and geographic boundaries, echoing dynamics observed in recent pandemics.