The tundra is probably the single most important amplifying carbon-cycle feedback. None of the IPCC’s climate models, however, include carbon emissions from a defrosting tundra as a feedback.
Yet, as NOAA reported last month, levels of methane (a far more potent greenhouse gas than CO2) rose last year for the first time since 1998, which may be an early indication of thawing permafrost. So it seems like a good a time for a review and update of what we know.
The tundra or permafrost is soil that stays below freezing (32 degrees F) for at least two years. Normally, plants capture carbon dioxide from the atmosphere during photosynthesis and slowly release that carbon back into the atmosphere after they die. But the Arctic acts like a freezer, and the decomposition rate is very low. The tundra is a carbon locker. We open it at our own risk.
We now know the Arctic contains far more carbon than previously thought ($ub. req’d) — nearly 1,000 billion metric tons of carbon (some 3600 billion metric tons of carbon dioxide). That exceeds all the carbon dioxide currently in the atmosphere. The permafrost may contain more than a third of all carbon stored in soils globally, much of it in the form of methane. Problem: Global warming is melting the top layer of permafrost, creating the possibility of large releases of soil carbon, and that is a potentially devastating vicious cycle. We are defrosting the tundra freezer — and at an unprecedented rate.
We know methane is bubbling up out of the tundra far faster than previously thought ($ub. req’d). In fact, a 2006 study ($ub. req’d) by Alaska researchers finds rapid degradation to key elements of the permafrost “that previously had been stable for 1000s of years.” The study, titled “Abrupt increase in permafrost degradation in Arctic Alaska,” concludes that this recent degradation exceeds changes seen earlier in the 20th century by a factor of ten to a hundred.
What’s happening in Siberia is even more alarming:
As New Scientist reported three years ago, a frozen peat bog in Western Siberia the size of France and Germany combined is turning into “a mass of shallow lakes,” some almost a mile wide. In the past 40 years, the region has warmed by 3 degrees C, greater warming than almost anywhere else in the world, in part because of the vicious cycle described earlier: Warming melts highly reflective ice and replaces it with dark soils, which absorb more sunlight and warm up, melting more ice, and on and on.
Russian botanist Sergei Kirpotin describes an “ecological landslide that is probably irreversible and is undoubtedly connected to climatic warming.” The entire western Siberian sub-Arctic region is melting, and it “has all happened in the last three or four years,” according to Kirpotin, who believes we are crossing a critical threshold. The peat bogs formed near the end of the last Ice Age some 11,000 years ago. They generate methane, which, up until now, has mostly been trapped within the permafrost, and in even deeper ice-like structures called clathrates. The Siberian frozen bog is estimated to contain 70 billion tons of methane (CH4). If the bogs become drier as they warm, the methane will oxidize and the emissions will be primarily CO2. But if the bogs stay wet, as they have been recently, the methane will escape directly into the atmosphere.
Either way, we have a dangerous vicious cycle, but the wet bogs are the worse because methane has 20 times the heat trapping power of carbon dioxide. Some 600 million metric tons of methane are emitted each year from natural and human sources, so if even a small fraction of the 70 billion tons of methane in the Siberian bogs escapes, it will swamp those emissions and dramatically accelerate global warming. Researchers monitoring a single Swedish bog, or mire, found it had experienced a 20 percent to 60 percent increase in methane emissions between 1970 and 2000. In some methane hotspots in eastern Siberia, “the gas was bubbling from thawing permafrost so fast it was preventing the surface from freezing, even in the midst of winter.”
Even if the tundra carbon is all emitted as carbon dioxide instead of methane, the consequences would be disastrous. Carbon emissions from human activity already exceed 8 billion tons a year, and we are on track to be at 11 billion tons a year by 2020. But as we have already seen, if we merely average 11 billion tons a year this century, then we will hit 1,000 ppm by 2100 and destroy the health and well-being of billions of people.
Has anyone ever modeled quantitatively how much tundra will be defrosted by rising CO2 concentrations? Yes — as we will see in my next post.