Amid blowout warm temperatures in the Arctic this year, two new studies have amplified concerns about one of the wild cards of a warming planet -- how quickly warming Arctic soils could become major contributors of greenhouse gases to the atmosphere, causing still greater warming.
In a major international study published last week in Nature Geoscience, a team of researchers from regions ranging from Alaska to Russia report that permafrost is thawing faster than expected -- even in some of the very coldest areas.
In these regions, winter freezing cracks open the ground, which then fills with water in the summer from melting snow. When refreezing occurs in the winter, that causes large wedges of ice to form amid the icy ground. These ice wedges can extend ten or fifteen meters deep, and can in some cases be thousands of years old.
But the study, sampling high Arctic sites in Russia, Alaska and Canada based on both field studies and satellite observations, found that across the Arctic, the tops of these wedges are melting, as the top layer of permafrost soil -- which itself lies beneath a so-called "active layer" of soil that freezes and thaws regularly -- also begins to thaw. "Landscape-wide ice-wedge degradation was observed at ten out of eleven sites," the paper reported.
"At the places where we have sufficient amounts of data we are seeing this process happen in less than a decade and even after one warm summer," says Anna Liljedahl, the lead author of the study and a researcher at the University of Alaska in Fairbanks.
"The scientific community has had the assumption that this cold permafrost would be protected from climate warming, but we're showing here that the top of the permafrost, even if it's very cold, is very sensitive to these warming events," Liljedahl continues.
The new study focuses specifically on the consequences of this ice wedge degradation for the region's hydrology. The melting of ice wedges redistributes water on a massive scale. It can flow out of the landscape and into rivers and the Arctic Ocean, says Liledahl. Or it pools in lakes.
However, the real implication is far broader, says Liledahl's co-author Ken Tape, also a professor at the University of Alaska in Fairbanks. "It's the first study where these features and changes have been documented across the Arctic," Tape says. "We've had occasional studies where they look at one place. That's a lot different than saying it's happening across the Arctic."
"It's a region that we thought up until recently would hold together a little bit better because there's so much cold permafrost, and so much cold down deep," Tape continues. "I think the idea was that it will be more stable than this."
The degrading of permafrost in this way won't just affect water, but also the planet's atmosphere, says another of Liljedahl's co-authors, the permafrost expert Vladimir Romanovsky, also of the University of Alaska in Fairbanks. "The degradation of ice wedges shows that upper part of permafrost is thawing, and thawing of the upper part of permafrost definitely is producing additional greenhouse gases," he says.
The problem is that as these frozen soils thaw, even for part of the year, microorganisms living within them can begin to break down dead but preserved plant life from eons past, and release their carbon in the form of carbon dioxide or methane. Romanovsky says he thinks that the Earth's atmosphere already contains more greenhouse gases than it might otherwise due to this thawing.
It has been estimated that Arctic permafrost contains roughly twice as much total carbon in its frozen depths as the entire planetary atmosphere does, because these landscapes have slowly stored it up over vast time periods.
And it's not just carbon dioxide in the atmosphere that results -- the melting of ice wedges leads to sinking ground and a bumpy, denatured landscape that impairs Arctic transportation and infrastructure. "Instead of having a relatively smooth landscape, which is really easy to drive a snowmachine on, you create this bumpy landscape, with bumps that could become a meter or two high," says Liljedahl.
There have been at least some arguments that there may be other factors that offset permafrost carbon emissions. Some have suggested, for instance, that more plants will grow in the warmer Arctic, sequestering more carbon, and that this will help offset permafrost losses.
But in the second study, just published in Environmental Research Letters, an expert assessment of nearly 100 Arctic scientists found little reason to believe there will be any factor that offsets permafrost emissions enough to reduce the level of worry.
The expert assessment led to the conclusion that, as the paper puts it, "Arctic and boreal biomass should not be counted on to offset permafrost carbon release and suggests that the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario."
These studies of permafrost are critical because of the underlying math of the climate change problem. There is a hard limit to how many greenhouse gases can be emitted if we want to avoid a given level of warming -- say, 1.5 degrees Celsius or 2 degrees Celsius above pre-industrial levels.
Researchers have even quantified the latter limit, suggesting we can't emit more than 1,000 billion tons, or gigatons, of carbon dioxide from 2011 and on if we want a two thirds or better chance of staying below 2 degrees C. The inevitable result is an extremely tight planetary carbon budget for the coming years.
Permafrost has the potential to upend all of that. The last thing the world needs, as it creaks into action to reduce emissions, is the emergence of a major new source of them, brought on by warming itself. Yet that's exactly what we're talking about here.
Granted, precisely how much carbon permafrost can emit and how fast that can happen remain big uncertainties. But given current scientific understanding, it could easily be well over 100 gigatons of carbon dioxide by the end of the century, or one tenth of the remaining carbon budget. In fact, it could be more than that.
"Ten percent is really something that you have to be aware and include it in any kind of projections of changes in greenhouse gases," said Romanovsky. "And I would say at this point it is still slow, but with further warming, probably by mid-century, these emissions will be much more."