Permafrost, as the name suggests, is supposed to remain frozen. Yet warming in the Arctic is melting this frozen layer beneath the Earth’s surface, releasing carbon dioxide and methane from its chilly clutches. In fact, the Arctic is warming at such a rate that even the equipment used to measure it is being swamped by rivers, researchers note in a study published in Nature last month.
First, what is permafrost?
Permafrost is a layer of frozen soil beneath the Earth’s surface with bits of rock and other organic matter frozen at or below 0°C (32°F) for two or more years in a row. The layer can range in thickness from between 1 meter and 1,000 meters (3.3 feet and 3,330 feet), and is typically found in Arctic regions such as Alaska, Greenland, and Siberia.
When permafrost melts, organic matter – dead plants, animals, and microbes – is released from its frozen chamber and begins to decay. This triggers the release of carbon dioxide or methane into the atmosphere, depending on the presence or absence of oxygen respectively. Current predictions suggest that a slow and steady rate of thawing will release a whopping 200 billion tonnes of carbon by the year 2299 if warming continues at its current rate. However, the Nature team say this could be “a vast underestimate”.
Around 20 percent of permafrost regions have features that make them susceptible to sudden thawing, which could ignite a domino effect of landslides and erosions strong enough to fell trees and redirect water from lakes. To top it off, many of these unstable regions are also the ones holding on to the most carbon in their frozen embrace.
"It’s a matter of how much ice there is frozen in the ground and what the slope of the landscape is," study author Dr Benjamin Abbott, assistant professor of ecosystem ecology at Brigham Young University, told IFLScience. "When you have chunks of ice in the ground they create voids when they melt and the surface collapses. Likewise, when you have sloping terrain, the whole skin of the tundra can slide off as the permafrost underneath begins to thaw."
The nature of the study
Recognizing this danger, the researchers tried to calculate just how much carbon could be released if such an abrupt thawing scenario were to happen. To do so, they synthesized results from studies already published in the literature in order to identify patterns in the collapse and recovery of the vast, yet fragile environment.
“We estimate that abrupt permafrost thawing in lowland lakes and wetlands, together with that in upland hills, could release between 60 billion and 100 billion tonnes of carbon by 2300,” the team note in the study. “This is in addition to the 200 billion tonnes of carbon expected to be released in other regions that will thaw gradually.”
They admit their estimates are rough due to the complicated nature of the research. To gain a more nuanced understanding of our changing world, they encourage extending measurement technology, funding monitoring sites, gathering more data, building holistic models, and improving reports.
"I thought this was is an excellent overview of the state of the science and some of the major research gaps," Dr Susan Natali, an Arctic scientist at Woods Hole Research Center who was not involved in the research, told IFLScience. "One of the things that makes the Arctic unique, in terms of the impacts of climate change, is that warming temperatures are altering the structure of the ground surface, resulting in severe hazards for people living in the region and, through carbon emissions, for people across the planet."
Damages to scientific equipment
Abrupt permafrost thawing can even surprise researchers: The team returned to their field sites in Alaska only to find that the land covered in trees a year ago were now lakes, crystal clear rivers now muddied with sediment, and hillsides liquefying to the point that they wipe out scientific equipment.
"We have had several field sites damaged by permafrost collapse and flooding," said Abbott. "One time we had a bunch of wooden stakes with temperature equipment pushed over by muskox and then the next week they had all been consumed by the gaping hole in the tundra. The pace of change in the Arctic is hard to believe if you haven’t seen it."
Natali has seen the effects first-hand too. "I have lost access to field sites because of flooding caused by ground subsidence and because of a collapsed road," she said. "In the scheme of things, these are minor inconveniences, when there are communities who are losing their homes, infrastructure, cultural resources, and access to subsistence food sources because of permafrost thaw and ground collapse."
Who does it affect?
"The brunt of the impact is being felt by people living in the Arctic and by vulnerable communities (e.g. coastal and fire-prone communities) across the globe," said Natali. "Coastal communities in the Arctic are especially at risk because they are impacted by the added hazards of increased storm damage, including erosion and flooding, caused by the loss of sea ice. The interactive effects of erosion, flooding, and permafrost thaw exacerbate ground collapse (described by the Yup’ik word, usteq)."
To be certain, the indirect effects of permafrost thaw will be felt globally if we do nothing about greenhouse gasses.
"Despite the uncertainties in the timing and magnitude of carbon emissions from thawing permafrost, there is no uncertainty that continuing fossil fuel emissions at our current rate will promote additional carbon release from permafrost. Reducing carbon emissions, for example, to limit warming to 1.5°C rather than 2°C, will save millions of square kilometers of permafrost, keeping large amounts of carbon frozen in the ground and out of the atmosphere," added Natali.