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Will thawing Arctic permafrost speed global warming?

Doug O'Harra
Permafrost sample site Hess Creek Photo courtesy of USGS Soil Carbon Research

The coming decades will thaw a growing expanse of permafrost in Alaska and across the Arctic. What will that mean?

Any Alaskan who’s spent time in trekking over summer tundra knows part of the answer -- a ripe-smelling slurry of boot-sucking muck will deepen and liquefy. It will smell rotten in the summer sun, and for good reason.

The sudden decay of organic matter deposited over centuries has the potential to dribble vast quantities of carbon dioxide and the super greenhouse gas methane into the air, boosting climate change and contributing to warmer temperatures throughout the region. But no one has ever been sure how much of the region’s stored carbon will be spewed as this process unfolds.

Now, 41 permafrost specialists have taken a new stab at adding up the potential of this pending Arctic belch, and it’s much worse than anyone thought.

The thawing of permafrost over the century will dump up to five times more carbon into the air than some previous estimates -- warming the Arctic by at least 3.5 degrees Fahrenheit by 2100, according to a survey of international scientists working together as the Permafrost Carbon Network.

Under the worst-case scenario, the scientists predicted that the Arctic region could heat up even faster, with increases in the average annual temperature of 4.5 degrees by 2040 and 13.5 degrees by 2100.

“Carbon will be released more quickly than models suggest, and at levels that are cause for serious concern,” wrote Edward Schuur from the University of Florida at Gainseville and Benjamin Abbott of the Institute of Arctic Biology at the University of Alaska Fairbanks, in a commentary published this week in the journal Nature.

“We calculate that permafrost thaw will release the same order of magnitude of carbon as deforestation if current rates of deforestation continue. But because these emissions include significant quantities of methane, the overall effect on climate could be 2.5 times larger.”

What does it mean?

The fate of permafrost across the Arctic and Alaska has become one of the most critical questions in climate change prediction, with scientists investigating the impact of wildfires, ancient carbon releases, gas bubbling up from tundra lakes, the slumping and thawing of still buried layers, and the carbon-producing activities of soil microbes.

“The latest estimate is that some 18.8 million square kilometres of northern soils hold about 1,700 billion tonnes of organic carbon -- the remains of plants and animals that have been accumulating in the soil over thousands of years,” the authors wrote. “That is about four times more than all the carbon emitted by human activity in modern times and twice as much as is present in the atmosphere now.”

“The larger estimate is due to . . . new estimates of the amount of organic carbon stored deep in frozen soils,” Abbott said in this story posted by the Institute of Arctic Biology. “There’s more organic carbon in northern soils than there is in all living things combined; it’s kind of mind boggling.”

One of the new insights from the survey: permafrost degradation won't depend solely on rising air temperature.

“In reality, permafrost can warm much more quickly,” Schuur and Abbott wrote. “If ice wedges melt, the ground can collapse, which accelerates permafrost thaw and causes trees to lean over as if drunk.”

(For a glimpse of “drunken trees” and other images of climate change in Alaska, plus much more detail about Alaska permafrost studies, check out the Permafrost Laboratory at the Geophysical Institute.)

Partly as a result, the process of permafrost breakdown is expected to feed on itself, moving faster as the decades pass, with the surface "active layer" that thaws each summer growing ever deeper as imore and more organic material gets exposed to decay.

The scientists estimate that the top 10 feet of permafrost will degrade by at least 9 to 15 percent by 2040 -- increasing to at least 47 percent by 2100 and as much as 79 percent by 2300.

Seep by seep, burp by burp, amount of carbon trickling out of the soggy earth will keep adding up -- 30 billion to 63 billion metric tons by 2040, rising up to 380 metric tons by 2100.

By year 2300, more than 865 billion metric tons of carbon could have entered the air from thawing permafrost alone. That's more than double all the carbon released so far by all of the cars, trucks, trains, ships, power plants and other human enterprises of modern times.  

Amplifying the overall climate warming

The scientists noted that the total amount of carbon freed by thawing permafrost will always remain smaller than the amount of CO2 and other greenhouse gases released directly by human activities.

But the emissions from the Far North will amplify the overall climate warming significantly, and must be measured accurately for climate models and any mitigation policies to do their work.

In some ways, the two scientists concluded, permafrost carbon will be more “problematic” to deal with than other sources of greenhouse gases.

“It occurs in remote places, far from human influence, and is dispersed across the landscape. Trapping carbon emissions at the source -- as one might do at power plants -- is not an option. And once the soils thaw, emissions are likely to continue for decades, or even centuries.”

“The latest estimate is that some 18.8 million square kilometres of northern soils hold about 1,700 billion tonnes of organic carbon -- the remains of plants and animals that have been accumulating in the soil over thousands of years,” the authors wrote. “That is about four times more than all the carbon emitted by human activity in modern times and twice as much as is present in the atmosphere now.”

Contact Doug O'Harra at doug(at)alaskadispatch.com.