Posts
The
Latest on the Threat for
Abrupt Methane Release
from the East
Siberian Sea
12
June, 2019
So
I just read the latest paper by Shakhova,
Semiletov and Chuvilin (2019)
released in the past week basically refreshing people on the threat
on abrupt methane release from the Eastern Siberian Arctic Shelf
(ESAS). The paper is linked above and seems to have been written for
scientists not directly in their field (more background and less
field specific jargon, except when directly relevant). For those who
not know, methane is a very powerful greenhouse gas (108 times as
potent at warming than carbon dioxide on a 10 yr timescale; near 150+
at 5 yrs or less). It is a short lived gas (after about 12 yrs, it is
converted to carbon dioxide and water). However, the methane
concentration in the atmosphere is rapidly increasing because of both
increasing industrial activity and releases from tropical and Arctic
sources. The East Siberian subsea region has huge stores of carbon in
the form of methane.
I consider Dr. Natalia Shakhova and Dr. Igor Semiletov the top scientists on the East Siberian Arctic Shelf and the huge threat from the methane stores there (accumulated during previous glacial periods and not released in significance during previous short interglacials). Other scientists critical of their work have not come close to the amount of field work they have done, nor understand the geophysical dynamics specific and unique to that area vs. other areas of the global ocean floor.
Discussion
In short, Shakhova, Semilitov & Chuvilin (2019) really do not hold back in this paper. They make it very clear the how and why behind the deterioration of methane hydrate stability (including the uncharacteristic lengthy natural Holocene era, now being "extended" by anthropogenic activity). For a general understanding of hydrates, see this link.
It also makes clear the certainty of continued rapid deterioration and increasing methane emissions because of 1) continued irreversible Arctic Ocean warming and sea-ice losses, 2) methane releases occurring all year round, not just in the warm season because of rapidly increasing open-water polynyas in the winter ice, 3), increasing storm activity in the Arctic mixing the shallow water layer over the continental shelf ("storm-induced CH4 pulses"), and 4) increasing vulnerability to tectonic activity. They also note that 5) "Because the ESAS composes ~8% of the world ocean continental shelf, its sedimentary drape area- and thickness-weighted fraction alone could contain 15 to 20% of global organic carbon inventory; Organic carbon provides the substrate for CH4 production."
There is also this (note that 1 teragram or "Tg" = 1 million tonnes. 1 billion tonnes is 1 gigatonne):
"It was suggested that ˃1400 Gt of CH4 could be preserved in the seabed of the ESAS [[90]. The current annual emission of CH4 to the atmosphere was calculated to be between 8 and 17 Tg annually [19][20]; this implies, conservatively, that equal amounts could have been potentially released annually during the previous climate epochs if permafrost had not restricted CH4 flux. Therefore, due to such restriction, during the time of one glacial period (~100 kYrs) ˃800 Gt of CH4 could have accumulated in the ESAS seabed as postponed potential fluxes. This amount of pre-formed gas preserved in the ESAS suggests a potential for possible massive/abrupt release of CH4, whether from destabilizing hydrates or from free gas accumulations beneath permafrost; such a release requires only a trigger."
In addition, they are critical of previous research by multiple research groups which they believe have serious methodology flaws and make note they are the only ones doing research of this kind in the ESAS (and in total have conducted the most extensive ocean floor survey of any region in the world). They, of course, also discuss past flaws in their methods which brought them to current conclusions.
Finally...and most blunt.
"Releases could potentially increase by 3–5 orders of magnitude, considering the sheer amount of CH4 preserved within the shallow ESAS seabed deposits and the documented thawing rates of subsea permafrost reported recently".
If you assume the current emissions rate averaged at 13 Tg/yr, that would mean abrupt releases 13,000 to 1,300,000 Tg/yr. 13 to 1300 gigatons. Basically they're making a case that the destruction of the subsea permafrost will lead to catastrophic releases of nearly all the gas (over years, not decades or nearly all at once) once the permafrost has become sufficiently weakened.
An abrupt release of methane would mean a significant acceleration in global warming, perhaps 1 degree C or more within years.
Here are links to other relevant papers by Shakhova et al. this decade:
Shakhova et al. (2017)
Shakhova et al. (2015)
Shakhova, Semiletov & Salyuk (2010)
For laypeople, here are a couple video intereviews with Shakhova which are must-sees.
YouTube Playlist
---Meteorologist Nick Humphrey
I consider Dr. Natalia Shakhova and Dr. Igor Semiletov the top scientists on the East Siberian Arctic Shelf and the huge threat from the methane stores there (accumulated during previous glacial periods and not released in significance during previous short interglacials). Other scientists critical of their work have not come close to the amount of field work they have done, nor understand the geophysical dynamics specific and unique to that area vs. other areas of the global ocean floor.
Discussion
In short, Shakhova, Semilitov & Chuvilin (2019) really do not hold back in this paper. They make it very clear the how and why behind the deterioration of methane hydrate stability (including the uncharacteristic lengthy natural Holocene era, now being "extended" by anthropogenic activity). For a general understanding of hydrates, see this link.
It also makes clear the certainty of continued rapid deterioration and increasing methane emissions because of 1) continued irreversible Arctic Ocean warming and sea-ice losses, 2) methane releases occurring all year round, not just in the warm season because of rapidly increasing open-water polynyas in the winter ice, 3), increasing storm activity in the Arctic mixing the shallow water layer over the continental shelf ("storm-induced CH4 pulses"), and 4) increasing vulnerability to tectonic activity. They also note that 5) "Because the ESAS composes ~8% of the world ocean continental shelf, its sedimentary drape area- and thickness-weighted fraction alone could contain 15 to 20% of global organic carbon inventory; Organic carbon provides the substrate for CH4 production."
There is also this (note that 1 teragram or "Tg" = 1 million tonnes. 1 billion tonnes is 1 gigatonne):
"It was suggested that ˃1400 Gt of CH4 could be preserved in the seabed of the ESAS [[90]. The current annual emission of CH4 to the atmosphere was calculated to be between 8 and 17 Tg annually [19][20]; this implies, conservatively, that equal amounts could have been potentially released annually during the previous climate epochs if permafrost had not restricted CH4 flux. Therefore, due to such restriction, during the time of one glacial period (~100 kYrs) ˃800 Gt of CH4 could have accumulated in the ESAS seabed as postponed potential fluxes. This amount of pre-formed gas preserved in the ESAS suggests a potential for possible massive/abrupt release of CH4, whether from destabilizing hydrates or from free gas accumulations beneath permafrost; such a release requires only a trigger."
In addition, they are critical of previous research by multiple research groups which they believe have serious methodology flaws and make note they are the only ones doing research of this kind in the ESAS (and in total have conducted the most extensive ocean floor survey of any region in the world). They, of course, also discuss past flaws in their methods which brought them to current conclusions.
Finally...and most blunt.
"Releases could potentially increase by 3–5 orders of magnitude, considering the sheer amount of CH4 preserved within the shallow ESAS seabed deposits and the documented thawing rates of subsea permafrost reported recently".
If you assume the current emissions rate averaged at 13 Tg/yr, that would mean abrupt releases 13,000 to 1,300,000 Tg/yr. 13 to 1300 gigatons. Basically they're making a case that the destruction of the subsea permafrost will lead to catastrophic releases of nearly all the gas (over years, not decades or nearly all at once) once the permafrost has become sufficiently weakened.
An abrupt release of methane would mean a significant acceleration in global warming, perhaps 1 degree C or more within years.
Here are links to other relevant papers by Shakhova et al. this decade:
Shakhova et al. (2017)
Shakhova et al. (2015)
Shakhova, Semiletov & Salyuk (2010)
For laypeople, here are a couple video intereviews with Shakhova which are must-sees.
YouTube Playlist
---Meteorologist Nick Humphrey
No comments:
Post a Comment
Note: only a member of this blog may post a comment.