The Black Death which ravaged Europe in the Middle Ages was triggered by a volcanic eruption, experts believe.
It is thought a volcanic eruption – or eruptions – caused temperatures to drop for consecutive years due to the haze from volcanic ash and gases, which in turn caused crops to fail across the Mediterranean.
The University of Cambridge studied ancient tree rings and found unusually cold and wet summers in 1345, 1346 and 1347, across much of southern Europe in the years leading up to the plague.
To combat the shortfalls, Italian city states began importing grain from farmers in the Black Sea region, and inadvertently brought in fleas carrying the bacterium Yersinia pestis, responsible for the Black Death.
“This is something I’ve wanted to understand for a long time,” said Prof Ulf Büntgen, from Cambridge’s Department of Geography.
“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.”
Although the new grain trade routes helped avoid famine, the ships enabled the first and deadliest wave of the plague to gain a foothold in 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 Dr Martin Bauch, a historian of medieval climate and epidemiology from the Leibniz Institute for the History and Culture of Eastern Europe.
“But ultimately, these would inadvertently lead to a far bigger catastrophe.”
Plague origins
The Black Death was one of the worst pandemics in human history. It devastated European populations from 1346 to 1353 and resulted in the deaths of an estimated 75 to 200 million people – 60 per cent of the population.
But despite intense multidisciplinary research, its geographic and chronological origins have remained in doubt.
Although it was assumed ships from the Black Sea had imported the deadly bacteria, it was never clear why grain was needed so urgently in the first place.
The new study suggests that volcanoes forced climatic downturn led to poor harvests, crop failure and famine.
As a consequence, the Italian maritime republics of Venice, Genoa and Pisa imported grain from the Mongols of the Golden Horde around the Sea of Azov in 1347.
Once the plague-infected fleas arrived in 14th-century Mediterranean ports on grain ships, they infected humans and rapidly spread across Europe, devastating the population.
The theory is boosted by the fact that some larger Italian cities, such as Milan and Rome escaped the Black Death because they never needed to import grain.
“In so many European towns and cities you can find some evidence of the Black Death, almost 800 years later,” said Prof Büntgen.
“Here in Cambridge for instance, Corpus Christi College was founded by townspeople after the plague devastated the local community. There are similar examples across much of the continent.”
The researchers say the “perfect storm” of climate, agricultural, societal and economic factors after 1345 led to the Black Death can also be considered an early example of the consequences of globalisation.
The research was published in the journal Communications Earth & Environment.