Vast areas of permafrost around the world warmed significantly over the past decade, intensifying concerns about accelerated releases of heat-trapping methane and carbon dioxide as microbes decompose the thawing organic soils.
The warming trend is documented in a new study published Wednesday in the journal Nature Communications. Detailed data from a global network of permafrost test sites show that, on average, permafrost regions around the world—in the Arctic, Antarctic and the high mountains—warmed by a half degree Fahrenheit between 2007 and 2016.
The most dramatic warming was found in the Siberian Arctic, where temperatures in the deep permafrost increased by 1.6 degrees Fahrenheit.
Along with increased greenhouse gas emissions, the disintegration of permafrost is causing big problems for communities in the Arctic by damaging roads and other infrastructure as the land destabilizes and erodes. The permafrost meltdown also threatens ecosystems with massive discharges of silt and sediments into rivers and coastal areas.
The findings, from what the authors describe as the first globally consistent assessment of permafrost temperature change, add to an exanding body of global warming evidence, including studies published in just the past week showing that the world's oceans have been warming at an accelerating rating and Antarctica has been losing six times more ice mass yearly than it was four decades ago.
"We can now say with certainty that permafrost is warming at the global scale," said Hugues Lantuit of the Alfred Wegener Institute for Polar and Ocean Research, a co-author of the new study.
Rate 'Suggests Substantial Change Underway'
Most permafrost areas have been frozen since the last ice age, about 10,000 years ago. They trap vast amounts of carbon in layers of frozen organic soil up to a mile thick.
By some estimates, the Arctic permafrost contains enough carbon to nearly double the amount of CO2 currently in the Earth's atmosphere. A rapid meltdown would be disastrous because it could release a lot of CO2—in addition to methane, a powerful short-lived climate pollutant—to the atmosphere, where it would cause additional warming, said Ted Schuur, a permafrost expert at Northern Arizona University.
"This rate of warming suggests substantial change underway," Schuur said. "This is important and often overlooked news. We often don't think about what we can't see deep under the ground."
Schuur said the study indicates that even areas with very old and cold permafrost, including parts of Greenland, may be more vulnerable than previously thought, with signs of thaw changes, like areas of sinking land, visible at the surface.
The temperature data, collected at an average depth of 45 feet into the permafrost at each site, will improve projections of future greenhouse gas emissions from thawing permafrost by providing a record of temperature increases measured by direct observations, said the study's lead author, Boris Biskaborn of the Alfred Wegener Institute.
The research also could help the 4 million residents of the Arctic prepare for the direct impacts of thawing permafrost by showing where to expect the greatest changes that could cause roads or bridges to fail or coastal permafrost bluffs to collapse.
Somewhat counterintuitively, the rapid rate of permafrost warming is very likely related to more snow, Biskaborn said. At some of the test sites, snow has been falling and accumulating earlier in the year. More shrubby vegetation, spurred by summer warming, keeps that snow from blowing away. It forms a thick insulating blanket that traps summer heat in the ground and prevents the ground from cooling off and refreezing.
Reinforcing Previous Permafrost Warnings
The findings in the new paper reinforce results from other recent studies. In 2017, scientists found a huge seasonal surge in greenhouse gas emissions in Alaska during autumn months linked with warming temperatures. Emissions from the October-December period had increased by 73 percent since 1975, and that increase correlated with rising summer temperatures in the region.
Columbia University Lamont-Doherty Earth Observatory climate researcher Róisín Commane, who led the research on seasonal emissions, said the new permafrost study reinforces concerns that greenhouse gas emissions from the Arctic could surge sharply as the region warms.
"My take home is that the anecdotal site thawing that I heard about this winter is part of a region-wide warming that seems to be accelerating faster in this decade than in previous decades," she said. "I think this means that older carbon that was once locked up in the permafrost will start to make it into the ecosystem and eventually the atmosphere," she said, adding that it's hard to make direct measurements of CO2 emissions from older carbon in thawing permafrost.
The study looked at 154 test sites, with 123 that included enough data to track the warming trend over the entire decade. The depth of the boreholes at the test sites help rule out the influence of seasonal temperature changes, so the observations show the steady warming caused by the buildup of greenhouse gases. The temperature increased at 71 sites, decreased at 12 sites and remained unchanged at 40 sites.
"It's nice to get a quasi-global picture of permafrost change and how trends differ between regions and/or permafrost types," said Mathias Göckede, a climate researcher at the Max Planck Institute for Biogeochemistry who was not involved in the study. "As I see it, their findings basically confirm what has been estimated before, but provides more details and a more solid foundation."