Large-scale release of permafrost carbon is likely. It is estimated that the amount of carbon stored in the polar north as soil permafrost or on the ocean bed as methane clathrates is around 1,670 billion tonnes, three times greater than the current quantity of atmospheric carbon. Losing even a third of the Arctic carbon stores would double atmospheric carbon dioxide levels and usher in warming of 4 degrees Celsius or more.
So the big question is how far we are from triggering large-scale permafrost release.
|PIOMAS yearly minimum Arctic ice volume
(click to enlarge)
- The first point to note is that the Arctic has already proved to be more sensitive to global warming that expected. It is now acknowledged that the Arctic has passed the tipping point for sea-ice-free summers. The lack of summer sea-ice will increase Arctic warming (already double the global average) as heat-reflecting ice is replaced by dark, heat-absorbing open seas. There may well be a summer sea-ice-free Arctic by around 2015 (see chart).
- Those circumstances will increase the rate of melting of the Greenland ice sheet, which is already accelerating. And now the tipping point for Greenland’s ice sheet (eventual sea level rise of 7 metres) has been revised down from around 3 degrees C to just 1.6C (uncertainty range of 0.8C-3.2C). At the current temperature rise of 0.8C we may have already reached Greenland’s tipping point, and with temperature rises in the pipeline (global emissions still rising, no reasonable agreement to reduce them), we are very likely to hit 1.6C in two to three decades.
- Global average temperatures have warmed just less than 1ºC since the Industrial Revolution, but average temperatures in Siberia, Alaska and western Canada are now 3ºC to 4ºC warmer than 50 years ago. In parts of northern Canada, Greenland and the surrounding ocean during the 2010-2011 northern winter, temperatures were more than 6 degrees Celsius warmer than the baseline temperature average for the period of 1951-1980, and 7 to 9 degrees Celsius above average over the Chukchi Sea. So by mid-century the regional increase increase could easily be 4ºC to 6ºC.
- Predictions in 2011 suggested that as soon as 2020 carbon emissions from melting permafrost could be close to a billion tonnes a year. Researchers said that this positive permafrost carbon feedback will “will change the Arctic from a carbon sink to a source after the mid-2020s and is strong enough to cancel 42–88% of the total global land sink.”
- Work by Celia Bitz, Philippe Ciais and others suggests that the tipping point for the large-scale loss of permafrost carbon is around 8–10C regional temperature increase. As temperatures rise, it is projected that Arctic amplification (the multiple by with the Arctic warms compared to the global average) would be approximately times three, so around a 3C increase in global temperature is probably more than enough to detonate the permafrost timebomb. This feedback in the carbon cycle would drive temperatures significantly higher. Caias told the March 2009 Copenhagen science conference that: “A global average increase in air temperatures of 2C and a few unusually hot years could see permafrost soil temperatures reach the 8C threshold for releasing billions of tonnes of carbon dioxide and methane”.
And now former UN climate chief Yves de Boer thinks that limiting warming to “two degrees is out of reach”, which makes Caias’s statement more than ominous. Of course, permafrost tipping points is not the only reason to view 2 degrees Celsius as a crazy outcome and to be avoided at all costs. NASA climate chief James Hansen concludes that at the current temperature, no “cushion” is left to avoid dangerous climate change, and that the Australian government target goals “… of limiting human-made warming to 2 degrees Celsius and CO2 to 450 ppm are prescriptions for disaster”.