Global warming could re-awaken ancient diseases and even the Black Death, according to an Oxford University professor.
Higher global temperatures would melt ice sheets that store long-buried bacteria, which could spread disease and potentially cause new global pandemics.
Professor Peter Frankopan offered his speculative prediction at the Cheltenham Literary Festival on Friday, as reported by The Times.
The professor of global history began by stating his view that there was "absolutely no chance" the international community would hit the Paris Agreement's target of keeping global temperature rises under 1.5C.
He said, "If we go over that degree change, it’s not about the Maldives being harder to visit on holiday or migration of people — it’s about what happens when permafrost unfreezes and the release of biological agents that have been buried for millennia."
And because ancient bacteria would be released again into the Earth's ecosystems, there would be a big risk of the global population being hit by diseases it can't handle.
Chief amongst such diseases is the plague, which Frankopan states was spread in the Middle Ages largely due to a rise in global temperatures.
"For example, in the 1340s, a 1.5-degree movement of heating of the earth’s atmosphere — probably because of solar flares or volcanic activity — changes the cycle of Yersinia pestis bacterium," he explained.
"That one and a half degree difference allowed a small microbe to develop into the Black Death."
According to Frankopan, such a possibility should be taken more seriously than a rise in sea levels or droughts, not least because the Black Death wiped out between 75 and 200 million people in Europe in the 14th Century.
"These are the things we should be hugely worried about," he said.
While his warnings draw a worst-case scenario for future global warming, there are recent examples of melting permafrost presenting a serious hazard to people.
In 2016, a 12-year-old boy died and over 40 people were hospitalized in Siberia, after having been infected by anthrax.
The anthrax had been released when high summer temperatures melted permafrost, which had kept a deer buried for decades following a previous outbreak of the dangerous bacteria.
Since this deer had been killed by anthrax, its exposure caused the previously frozen bacteria to be released into the area's water and soil, where it then entered the food chain.
Over 1,500 reindeer were infected and killed as a result, and since some of these had been eaten by local residents, they too were infected.
Frankopan's predictions also come amid a growing slew of studies examining some of the more indirect effects of global warming.
Yesterday, an international team of climate scientists publishing in the Nature Plants journal wrote that severe climate change would cause worldwide beer shortages.
Last month, a paper published in the influential Nature journal concluded that global warming is already causing a rise in large landslides and tsunamis.
While in July, researchers at Stanford University published research which found that rising global temperatures could result in 40,000 more suicides in the US and Mexico by 2050.
This story originally appeared in The Sun.