🌋 Could a volcanic eruption be the origin of the Black Death in Europe?

The 14th century in Europe was marked by a demographic upheaval of unprecedented scale with the Black Death. An interdisciplinary study published in Communications Earth & Environment reconstructs the chain of causality, where a distant natural event directly conditioned the course of human history by creating the conditions for large-scale pathogen transfer.

The study conducted by a team of historians and geographers does not simply analyze the spread of the bacterium Yersinia pestis. It meticulously traces how a sudden climatic disturbance disrupted the agricultural and commercial systems of the Mediterranean, forcing decisions that had tragic consequences. This approach makes it possible to understand why the pandemic struck with such violence at a precise moment, and not decades earlier or later.

The signature of a forgotten volcano in the 14th-century climate

Ice cores extracted from Greenland and Antarctica reveal a sulfate peak around the year 1345. The similarity of concentrations at both poles indicates a major volcanic eruption, likely located in the tropics. This event projected a veil of aerosols into the stratosphere that filtered solar radiation for several years. The growth rings of European trees, particularly sensitive to temperature, record the direct consequences of this episode.

Dendrochronological data show that the summers from 1345 to 1347 were exceptionally cold in southern Europe. The narrow growth rings, even "blue rings," testify to significant physiological stress in trees. At the same time, medieval chronicles report unusual optical phenomena, such as abnormally dark lunar eclipses or a persistently veiled sky. These historical accounts perfectly corroborate the physical evidence of a prolonged volcanic winter.

This period of rapid cooling had an immediate and severe impact on Mediterranean agriculture. Grain and vine harvests, dependent on sufficient summer temperatures, suffered repeated failures. Soils, already weakened by abnormally wet autumns, experienced increased erosion. Within a few years, a structural food shortage situation set in, jeopardizing the supply of densely populated cities in Italy.

From food crisis to the introduction of the pathogen

Faced with local famines, powerful Italian maritime republics like Genoa and Venice had to resort to massive wheat imports. Their already extensive trade networks turned to the grain granaries of the Black Sea, under the control of the Mongol Golden Horde. Agreements were concluded in the spring of 1347 to lift embargoes and organize emergency maritime convoys. This logistical reaction, although vital to feed the populations, created a direct corridor between an area where the plague was endemic and the heart of Europe.

The ships returning from Crimea in the summer of 1347 carried far more than grain in their holds. Researchers suggest that fleas infected with Yersinia pestis survived the long journey by feeding on grain dust and organic residues. This passive mode of transport, already documented in the early 20th century, would have allowed the pathogen to cross the Black Sea and the Mediterranean without requiring live hosts for the entire crossing.

The arrival of these ships in Italian ports chronologically coincides with the first human plague outbreaks. Venice and Genoa were affected just weeks after the cargoes were unloaded. The epidemiological cycle could then begin: infected fleas first contaminated urban rodent populations, before transferring to humans once their primary hosts were decimated. The commercial infrastructure, designed to address a climatic crisis, had become the vector of a health catastrophe.