Permafrost – soil that has been frozen for at least two years – is more sensitive and susceptible to global warming than previously thought, the scientists found, in the first study to quantify how much permafrost could be lost due to climate change.

“The amount of permafrost that thaws under global warming is going to be very large, and this is the first time we’ve really put numbers on it,” said Sarah Chadburn, the lead author of the study and a research fellow at the University of Exeter on Monday.

Permafrost, mostly found in high-latitude regions like the Arctic, stores large quantities of carbon dioxide and methane, which are released into the atmosphere if the soil melts and decomposes, according to the researchers from Exeter, the University of Leeds, and Britain’s official weather service, the Met Office.

Their study, published in the journal Nature Climate Change, found that for every degree the world warms, 4 million sq km of permafrost would be lost.

An increase in global warming by 2 degrees Celsius would thaw more than 40 per cent of the earth’s permafrost, according to the study.

The 2015 Paris Agreement on climate change aims to limit this, by using the cooperation of almost 200 countries to attempt to keep the global temperature increase “well below” 2 degrees Celsius above pre-industrial levels.

But at the current level of warming, Chadburn said, “you could lose almost all of the permafrost”.

An estimated 35 million people currently live in cities or towns on top of permafrost, and thawed soil could cause the ground to become unstable, the scientists said.

The researchers said this would put buildings, roads and other infrastructure at risk of collapsing.

“The ability to more accurately assess permafrost loss can hopefully feed into a greater understanding of the impact of global warming and potentially inform global warming policy,” co-author Eleanor Burke, a permafrost research scientist with the Met Office, added in a statement.

– Reuters