Rare set of varied factors triggered Black Death

Tree ring data enabled Büntgen et al. To determine whether a volcanic eruption (or a group of eruptions) occurred around 1345, look specifically at the so-called “blue rings” that indicate unusually cold or wet summers – in this case, for three consecutive years (1345, 1346 and 1347). Textual sources also mention details such as unusually high levels of clouds and a black lunar eclipse, which are indicative of the after-effects of volcanic activity.

That cold climate in turn led to widespread crop failures and famine, especially in Spain, southern France, Egypt, and parts of northern and central Italy. While Milan and Rome were largely self-sufficient, according to the authors, smaller urban centers such as Bologna, Florence, Genoa, Sienna, and Venice depended on a complex grain supply system to import grain from the Mongols of the Golden Horde through trade routes established along the Black Sea coast. Textual evidence supports this, showing a substantial price increase for grain and the imposition of grain trade regulations in 1346. This saved people from starvation but also introduced Y. pestis with devastating consequences.

According to the authors, while the factors that spread the Black Death to Europe are unique, the study reflects the risks of a globalized world and calls for a similar interdisciplinary approach to future threats. “Although a combination of factors contributing to the Black Death appears rare, the likelihood of zoonotic diseases emerging and turning into pandemics under climate change is likely to increase in a globalized world,” Büntgen said. “This is particularly relevant given our recent experiences with COVID-19.”

Communicating Earth and Environment, 2025. DOI: 10.1038/s43247-025-02964-0 (About DOI).