The Black Death moved across Europe from 1347 to 1353 CE, with mortality rates reaching as high as 60% in some areas. Although its impact is well documented, the precise reasons for when and how the pandemic began remain unclear.

Climate Records Reveal Signs of a Major Eruption

To explore these questions, Martin Bauch and Ulf Büntgen evaluated earlier research on tree ring growth from eight regions in Europe, measurements of volcanic sulfur preserved in Antarctic and Greenland ice cores, and written reports from the fourteenth century. Together, these records point to a significant volcanic eruption somewhere in the tropics around 1345 CE. The eruption appears to have increased atmospheric sulfur and ash, which contributed to colder and wetter conditions across southern Europe and the Mediterranean.

Historical accounts describe widespread crop failures and famine during this period in Spain, southern France, northern and central Italy, Egypt, and the Levant. These hardships prompted Italian maritime powers — such as Venice and Genoa — to negotiate a ceasefire in a conflict with the Mongols of the Golden Horde so they could secure grain shipments from the Black Sea region around 1347 CE.

Grain Imports and the Possible Spread of Plague

Venetian sources state that these imports helped prevent mass starvation. However, the timing of arriving grain ships and the first plague outbreaks in cities that received them raises another possibility. Fleas carrying Yersinia pestis may have traveled with the grain. As the shipments were moved to additional cities, including Padua, these fleas could have helped accelerate the spread of the Black Death throughout Europe.

The authors conclude that this combination of climatic disruption, famine, and grain transport offers a plausible explanation for how the Black Death began and spread across Europe.