Climate-driven changes in Mediterranean grain trade mitigated famine but introduced the Black Death to medieval Europe

The first wave of the second plague pandemic, the Black Death, claimed much of Europe’s human population in just a few years after 1347 CE. While it is accepted that the causative bacterium Yersinia pestis originated from wildlife rodent populations in central Asia and reached Europe via the Black Sea region, reasons for the timing, spread and virulence of the onset of the Black Death are still debated. Here, we argue that a post-volcanic climate downturn and trans-Mediterranean famine from 1345–1347 CE forced the Italian maritime republics of Venice, Genoa and Pisa to activate their well-established supply network and import grain from the Mongols of the Golden Horde around the Sea of Azov in 1347 CE. This climate-driven change in long-distance grain trade not only prevented large parts of Italy from starvation but also introduced the plague bacterium to Mediterranean harbours and fueled its rapid dispersal across much of Europe. Post-volcanic climate downtown in southern Europe around 1345–1347 CE caused widespread famine, leading to Italian maritime republics importing grain from the Black Sea region and introducing fleas carrying the plague bacterium that caused the Black Death, according to tree ring analysis and documentary sources.