The Black Death may have decimated the medieval European population in part because of volcanic eruptions that took place several years prior, according to a new study.
Researchers found that a spell of unusually cold summers in the mid-1340s – likely linked to one major volcanic eruption or several smaller ones – contributed to severe famine across the Mediterranean.
The knock-on effects, they argue, ultimately brought plague-bearing fleas into European ports, where the disease went on to kill up to 60 per cent of the population.
“This is something I’ve wanted to understand for a long time,” said Professor Ulf Büntgen, a palaeoclimatologist from the University of Cambridge’s geography department. “What were the drivers of the onset and transmission of the Black Death, and how unusual were they?
“Why did it happen at this exact time and place in European history? It’s such an interesting question, but it’s one no one can answer alone.”
Büntgen told BBC Science Focus how clues from tree rings and ice cores (layers of ancient ice that capture chemicals from old volcanic eruptions), pointed towards volcanic activity as the culprit for an unusual climate.
“If we see a certain year was particularly cold or warm or dry or wet, we want to understand why,” Büntgen told BBC Science Focus.
“We often collaborate with ice core experts to get an idea about past volcanic eruptions, because volcanoes release a lot of sulphur very high in the atmosphere.
“That can – and often does – cause a cold summer afterwards. It’s post-eruption cooling.”
It was up to climate historian Dr Martin Bauch – from the Leibniz Institute for the History and Culture of Eastern Europe, in Germany – to connect this climate data to historical records.
He found that this cold weather caused a huge famine across the Mediterranean region – and that it was the reactions of the Italian republics of Venice, Genoa and Pisa that ultimately brought the plague to Europe.
“For more than a century, these powerful Italian city states had established long-distance trade routes across the Mediterranean and the Black Sea, allowing them to activate a highly efficient system to prevent starvation,” said Bauch. “But ultimately, these would inadvertently lead to a far bigger catastrophe.”
Fleas infected with the plague bacterium Y. Pestis likely arrived at Mediterranean ports on these grain ships, where they jumped to rats, cats and humans and rapidly spread across Europe, decimating the population.
In this way, volcanic activity prompted a series of events that ultimately brought plague to medieval Europe, the study concluded.
Büntgen said this story had implications for the modern world, seven centuries later.
“Although the coincidence of factors that contributed to the Black Death seems rare, the probability of zoonotic diseases emerging under climate change and translating into pandemics is likely to increase in a globalised world,” he explained.
“This is especially relevant given our recent experiences with COVID-19.”
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