More permafrost than thought may be lost as planet warms

By Henry Fountain, New York Times News Service

Wednesday, April 12, 2017 | 12:02 a.m.

As global warming thaws the permafrost, the frozen land that covers nearly 6 million square miles of the Earth, a big question for scientists is: How much will be lost?

The answer, according to a new analysis: more than many of them thought.

A study published Tuesday in the journal Nature Climate Change suggests that as the planet warms toward 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels, each degree Celsius of warming will lead to the thawing of about 1.5 million square miles of permafrost.

That figure is at least 20 percent higher than most previous studies, said Sarah E. Chadburn, a researcher at the University of Leeds in England and the lead author of the study.

“Previous estimates of global changes in permafrost were done using climate models,” Chadburn said. “Our approach is more based on using historical observations and extrapolating that to the future. It’s a very simple approach.”

Permafrost thaws slowly over time, but it is already causing problems in the Arctic, as slumping ground affects building foundations, roads and other infrastructure in places like the North Slope of Alaska, Yukon and parts of Siberia. The thawing also contributes to climate change, as warmed-up organic matter is decomposed by microbes, releasing more greenhouse gases into the atmosphere.

Chadburn and her colleagues looked at how much permafrost would thaw if temperatures were to stabilize at a warming of 2 degrees Celsius, long a target of climate accords, or at 1.5 degrees, which the 2015 Paris agreement set as an ambitious goal.

A 2 degree increase, the researchers found, would lead to a loss of about 2.5 million square miles of permafrost compared with a 1960-90 baseline, or about 40 percent of the current total.

The study showed the advantages to be gained from limiting warming to 1.5 degrees: Thawing would be reduced by about 30 percent, or 750,000 square miles.

But the research also shows the potentially devastating consequences of missing either of those targets. Warming of 5 degrees Celsius (9 degrees Fahrenheit) would leave at most about 1 million square miles of permafrost, or less than 20 percent of the current total.

Edward A.G. Schuur, a permafrost expert at Northern Arizona University, said the study was “an important and interesting calculation of where permafrost will be at some distant point in the future as we undergo climate warming.”

“What’s really important is this is based on totally different assumptions,” Schuur said. “It’s useful because it gives us a different perspective.”

Chadburn said her study did not delve into the details of how different permafrost areas might be affected. Schuur said that as the planet warms, more southerly regions, where the permafrost occurs in discontinuous patches, would be expected to thaw first.

But there will still be changes even in areas of extensive permafrost in the far north, Schuur said.

“There will be surface changes that affect everyone who lives there,” he said. “I don’t think there’s any place in the permafrost zone that’s remote enough to escape changes.”