An unknown volcanic eruption (…) triggering a cool and overcast period in the Mediterranean, the eruption started a domino effect that led to a downturn in agricultural production, which required merchants to import grain — and the bacterium Yersinia pestis that causes bubonic plague — via the Black Sea.

“Unknown”?

When combing through contemporaneous historical accounts, the researchers noticed reports of reduced sunshine, increased cloudiness and a dark lunar eclipse, all independently reported by observers in parts of Asia and Europe between 1345 and 1349. All of these astronomical and weather phenomena could be attributed to a large-scale volcanic aerosol layer