Terrestrial Permafrost – the Threat from Thawing

Australia: The Land Where Time Began

Terrestrial Permafrost – the Threat from Thawing

The greatest immediate threat is the Arctic offshore, though the threat from CO₂ emissions from decaying permafrost on land is also real and inexorable. It is known as a result of the work of Arctic biologists that the previously frozen vegetation that is exposed and rots when permafrost on land thaws passes through a series of chemical and biological processes that end in the production of methane and CO₂. This differs from the situation of offshore permafrost in the Arctic in which methane is already present and ready to be released as the permafrost thaws.

An area of about 19 million km² of permafrost is present in the world, which includes both continuous and discontinuous, or patchy, permafrost. Areas of permafrost have warmed by 2^oC-3^oC since the 1980s, and it is thawing. Permafrost emits a mixture of methane, CO₂, and some nitrous oxide (N₂O), all of which are greenhouse gases, as it thaws. The quantity of carbon that is contained in this permafrost is 1,400-1,700 Gt, according to the IPCC. It has been estimated that 110-230 Gt will be lost, as both carbon dioxide and methane, by 2040, and 800-1,400 Gt by 2100, at a rate of 4-8 Gt per year prior to 2040, and rising to 10-16 Gt per year after 2040 until 2100.

Wadhams suggests noting these figures. This would mean that by 2100 the quantity of carbon emitted from thawing permafrost on land is about 30 times greater than the pulse of offshore methane, which has been suggested to be 50 Gt, that is expected to be released over the next decade. It is not certain how much of this carbon will be in the form of hyperactive methane, though it is probably substantial. Therefore it is inevitable that there will be a major boost to climate warming, that may be rapid, due to the thawing of offshore permafrost releasing trapped methane; or it may be slow, due to the formation of methane by the thawing of terrestrial permafrost; or it may be fast and slow, a pulse from offshore permafrost, which is followed by a slower, though larger, release from onshore permafrost. This boost to warming is certain to occur before 2100 at the latest.

Another aspect of the 2013 IPCC assessment is that these figures on methane emissions from terrestrial permafrost are quoted, but the implications for accelerated climate change are not, even though the implications are as bad, or even worse, than the implications for the release of methane from offshore permafrost.

Widening of the area

The pace of the exploration of the Arctic shelves has intensified following the discoveries made by Shakhova and Semiletov, which has yielded more discoveries of warm water offshore and the production in the shelf areas other than the East Siberian Sea.

The area of operations of Shakhova and Semiletov was expanded out of the East Siberian Sea when they joined the Swedish icebreaker Oden for the ‘SWERUS-C3’ cruise to the Laptev Sea in the summer of 2014. On the outer shelf at a depth in the water of 200-250 m a zone of several kilometres across was found where large volumes of bubbles of methane were being emitted , and closer to the shore 100 methane sources were found on the sea bed at depths of 60-70 m, including an intense methane outbreak at 62 m which was termed by the Chief Scientist, Örjan Gustafsson, a ‘mega methane flare’. It was announced that elevated methane levels, about 10 times higher than background seawater’, was in the surrounding water column. Methane was produced by a borehole in the sediments of the shelf.

A research station mooring that had been in place on the shelf since 2007 at a water depth of 40-50 m, measuring the temperature of the full water column down to the seabed, and the ice thickness. In the summer of 2012 the instruments recorded an early ice cover retreat and warming at mid-depth, that had been driven by a combination of penetrating solar radiation and heat that had been delivered by the outflow of the Lena River. The heat had mixed downwards to the seabed, though it took time to reach the seabed, arriving at the sediment surface in winter when the seabed water warmed up, reaching 0.6^oC in January 2013, and remained at that temperature for 2.5 months. Wadhams suggests that this would have a melting effect on the sediments, and it linked the warmer water to the methane that had been observed in 2014 by ‘SWERVUS C-3’. The suggestion that the Laptev Sea could be a larger methane source than the East Siberian Sea has been supported by model studies.

The conclusion that seabed methane emission is not confined to the East Siberian Sea, being found in more, and possibly all, Arctic shelf waters, is suggested by the strength of the activity found in the Laptev Sea. Wadhams suggests that estimates of methane emission probably still underestimate the actual level of emission. It has been revealed by in situ monitoring of atmospheric methane levels in the Arctic that there are occasional peaks that are well above background levels, termed ‘dragon breath’, as each of these peaks appears to represent an exceptional emission from a single source. It has been suggested that they may originate in individual mega flares that have not been observed. It is shown by the record from a methane monitoring station at Alert, on the northern tip of Ellesmere Island, that methane levels that had stabilised at 1,852 ppb in 2000, have now been rising at an accelerating rate, reaching 1,940 ppb, and most of this increased has occurred in the last 3-4 years.

Wadhams also suggests that the finding of 3 craters with smooth vertical walls in the northern Siberian tundra in 2014, which are surrounded by deposited soil material, is possibly also relevant. The most plausible explanation is that they were formed by underground methane explosions, in which the thawing permafrost allowed the buildup of methane beneath a sediment cap, which eventually blew the cap out in a great explosion.

It is strongly suggest by all these events that the emission of methane is already occurring in the coastal regions of the Arctic, which makes use of mechanisms that have never previously been observed. Wadhams says it is important that the threat posed by this emission to climate, a threat that is immediate, in spite of it being belittled by the IPCC Fifth Assessment.

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