When we think about the Arctic in a warming world, we tend to think about sharp declines in sea ice and — that powerful symbol — the polar bear. But that’s far from the only problem that a melting Arctic brings.
In the past decade, scientists have been training more attention on another deeply troubling consequence. Rapid Arctic warming is expected to lead to the thawing of a great deal of frozen soil or permafrost, which, as it thaws, will begin to emit carbon dioxide and methane to the atmosphere. And if this occurs in the amounts that some scientists are predicting, it could significantly undermine efforts to reduce the world’s greenhouse gas emissions.
Indeed, scientists have discovered a simple statistic that underscores the scale of the potential problem: There may be more than twice as much carbon contained in northern permafrost as there is in the atmosphere itself. That’s a staggering thought.
Permafrost is simply defined as ground that stays frozen all year round. There’s a lot of it – it covers 24 percent of the surface of the northern hemisphere land masses, according to the International Permafrost Association. But more and more of it is thawing as the Arctic warms, and these frozen soils contain a vast amount of organic material — largely dead plant life — in a kind of suspended animation.
“It’s built up over thousand and thousands of years,” says Robert Max Holmes, a senior scientist at the Woods Hole Research Center. “It’s all stored away in a freezer, and as we’re warming the Earth, and warming the Arctic, it’s starting to thaw.”
As permafrost thaws, microbes start to chow down on the organic material that it contains, and as that material decomposes, it emits either carbon dioxide or methane. Experts think most of the release will take the form of carbon dioxide — the chief greenhouse gas driving global warming — but even a small fraction released as methane can have major consequences. Although it doesn’t last nearly as long as carbon dioxide in the atmosphere, methane has a short-term warming effect that is many times more powerful.
Among the potential mega-problems brought on by climate change, including melting ice caps to the slowdown of the ocean conveyor system, permafrost emissions are unique. For it’s not merely about sea level rise or weather changes — it’s about amplifying the root problem behind it all, atmospheric carbon levels.
The emission of carbon from thawing permafrost is what scientists call a “positive feedback.” More global warming could cause more thawing of Arctic permafrost, leading to more emissions of carbon into the atmosphere, leading to more warming and more thawing of Arctic permafrost — this does not end in a good place.
Moreover, in a year in which the world will train its attention on Paris and the hope for a new global climate agreement, permafrost emissions could potentially undermine global climate policies. Even as the world starts to cut back on emissions, the planet itself might start replacing our emissions cuts with brand new carbon outputs.
All of this, and the Arctic permafrost problem hasn’t received much attention — yet. “The concept is actually relatively new,” says Kevin Schaefer of the National Snow and Ice Data Center at the University of Colorado in Boulder. “It was first proposed in 2005. And the first estimates came out in 2011.” Indeed, the problem is so new that it has not yet made its way into major climate projections, Schaefer says.
“None of the climate projections in the last IPCC report account for permafrost,” says Schaefer. “So all of them underestimate, or are biased low.”
To understand why northern soils contain so much carbon it helps to understand why southern or tropical soils don’t. It all comes down to temperature, and how that affects how quickly microorganisms break down dead organic material (plant and animal life), causing it to release its carbon back into the atmosphere.
In temperate latitudes, it’s simple: Plants grow and pull carbon dioxide from the air — then they die, decompose and emit it back again. “In warmer temperatures, microbial activity will go on over all of the year,” says Vladimir Romanovsky, a permafrost researcher at the University of Alaska, Fairbanks. “So even if productivity in warmer climates [is] larger, there’s not much sequestration of carbon in the soil.”
But in permafrost regions, it’s very different. Plants grow much more slowly, and there are fewer of them — but their decomposition is also much slower, explains Romanovsky. So a large amount of organic material gets stored in the frozen ground. And this has been happening, in some cases, over tens of thousands of years since the last ice age, leading to a truly vast carbon store that is stuck in place — or, at least, it used to be.
“As long as the carbon stays frozen in permafrost, it’s stable,” says Schaefer. “It’s kind of like broccoli in your freezer. But if you take that out, it eventually thaws out and goes bad.”
The problem, in this case, is the size of the freezer. Just consider some basic numbers. According to a 2013 report from the National Academy of Sciences, northern permafrost contains 1,700 to 1,850 gigatons of carbon — a gigaton is a billion metric tons — which is more than double the amount of carbon currently in the atmosphere (730 gigatons, says the NAS). And over 1,000 of those gigatons are thought to be stored in the top three meters of permafrost soil.
Nobody’s saying all of that is going to come out — certainly not immediately, and maybe not ever. However, as the Arctic continues to warm over the course of the century, emissions from permafrost could ramp up, and they could eventually reach a scale that could begin to offset climate gains. “It’s certainly not much of a stretch of the imagination to think that over the coming decades, we could lose a couple of gigatons per year from thawing permafrost,” says Holmes.
So far, permafrost emissions, if any, are pretty small. But by 2100, the “mean” estimate for total emissions from permafrost right now is 120 gigatons, says Schaefer. That’s no small matter, considering that according to the U.N.’s Intergovernmental Panel on Climate Change and the National Academy of Sciences (see above), the world can only emit about 1000 total gigatons of carbon if we want to have a good chance of limiting the temperature rise to less 2 degrees Celsius of warming since 1860-1880.
According to the IPCC, the world had already emitted 515 gigatons by 2011, leaving a pretty tight remaining carbon “budget.” Permafrost emissions, if they’re big enough, could lead to busting the budget a lot quicker.
The world has been focused on some Arctic emissions problems lately that sound a lot like the thawing permafrost emissions problem, but should probably be distinguished from it. For instance, there is the concern about weird craters that have been found in northern Siberia, and the idea that these might be the result of methane explosions from permafrost.
While there’s still debate over how the craters were formed, though, it’s not clear that we’re talking about the same phenomenon. One reason? The craters are very far to the north in the area around the Yamal Peninsula, and that’s not where the thawing permafrost emissions problem is expected to first emerge. Rather, it should be the opposite — at the southern rim of where permafrost is found.
“The further south you go, the warmer it is, so the more vulnerable the permafrost is to thawing,” says Schaefer. “So all the emissions will be dominated by the southern margins, southern Alaska, Hudson Bay.”
Nonetheless, the craters have gotten vastly more media attention — because they’re mysterious, and because they’re thought to reflect dramatic methane explosions. But ultimately, the steady, long-term problem of carbon loss from permafrost may be scarier.
Later this month — on April 24 — the United States takes over the chairmanship of the Arctic Council, a group of eight nations with Arctic territories that helps to coordinate policy for the region. The State Department has specifically indicated that one of the focuses of the two-year chairmanship will be the issue of climate change. So, will permafrost emissions enter into policy considerations?
“This is a dangerous feedback loop as Arctic warming drives permafrost thaw, and the permafrost releases more GHGs into the atmosphere, accelerating change,” said a State Department official. “However, many questions remain about the processes by and time scales over which such emissions could be released into the atmosphere.”
The official said that through the Arctic Council, the United States will emphasize better monitoring and observation systems to detect emissions from permafrost. But the officials also underscored the importance of “an ambitious international climate agreement in Paris – this is where we need action to slow climate change.”
The concern is whether such an agreement will arrive soon enough to stop or at least blunt the permafrost problem. It’s “a true climatic tipping point, because it’s completely irreversible,” says Schaefer. “Once you thaw the permafrost, there’s no way to refreeze it.”
Updated: This article was changed to remove some references to “melting” permafrost. Permafrost thaws, rather than melts. Also, the treatment of the planet’s carbon budget and how it could be affected by permafrost emissions was changed because in a previous version of the text, some figures were in gigatons of carbon dioxide, rather than gigatons of carbon.
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