Revkin may turn out to be right not to worry (people are usually right when they tell you not to worry) but his article is misleading and sloppy:
* He conflates two different papers * He references the recent article in the Independent about Semiletov's trip to the Shelf, but doesn't talk to Semiletov or get any information about his recent expedition
I sent several emails to Semiletov and others in his group since the AGU presentation. Happy to post when and if there's input from them on the points made by other scientists gauging the long-term risk question. Witnessing a lot of emissions now is important information, and monitoring is essential in such regions. But drawing conclusions about overall risk from this is not possible unless setting those observations against both basic understanding of sub-sea permafrost response to ocean warming and what can be learned by looking back 8,000 years ago etc.
Andy Revkin, the feeling I got from reading your piece is that there is nothing to worry about WRT Arctic methane. Is this so?
You write for instance:
That’s the understatement of the year considering their conclusion that even under sustained heating, the brunt of the sub-sea methane won’t be affected in this millennium.
Just as it isn't about the entire Greenland and Antarctic ice sheets, but about how fast the amount of melted ice sheet needed to elevate sea level by 1-2 meters could come about, it isn't about the "brunt of the sub-sea methane" either.
If I've understood correctly, there could be about 1400 to 2200 billion tons of sub-sea methane (the estimates vary). In Shakhova et al. (2008) it is estimated that "release of up to 50 Gt of predicted amount of hydrate storage [is] highly possible for abrupt release at any time". That would increase the methane content of the planet's atmosphere by a factor of twelve. (source: Wikipedia)
50 Gt of 1400 Gt (lowest estimate) is 3.6%. Methane currently has a forcing of 0.5 W/m2 (if I've understood correctly).
I'm probably making some sort of mistake, but here goes: So if 3.6% of the sub-sea methane would be released - hardly the "brunt" I would say -, this forcing would increase twelvefold to let's say 6 W/m2 (CO2 currently is 1.6 W/m2).
If this is correct, I'd be inclined to say 'Apocalypse perhaps not immediately but definitely not "Apocalypse not"'.
To correct my own stupidity: the impact of a forcing doesn't increase linearly, so 12 x 0.5 W/m2=6 W/m2 is too simple. Nevertheless, my question still stands. What happens when 2.5%-3.5% of the sub-sea methane stores gets released (the non-brunt, if you will)? How long/much warming would that take? Is there a correlation with Arctic sea ice?
Coincidentally global methane concentration started rising again in 2006, around the time when we saw the 'shift' in Arctic summer sea ice melt.
Thanks, Belette. Does that substantially alter the point of my question? Revkin talks about the brunt of sub-sea methane not gassing out this millennium. I figure just 2-3% would be enough to have a marked impact. Is that enough not to casually dismiss Arctic methane as a potential threat? Or is it 'Apocalypse not', like Revkin asserts?
7 comments:
Revkin may turn out to be right not to worry (people are usually right when they tell you not to worry) but his article is misleading and sloppy:
* He conflates two different papers
* He references the recent article in the Independent about Semiletov's trip to the Shelf, but doesn't talk to Semiletov or get any information about his recent expedition
http://bit.ly/s9HK9d
I sent several emails to Semiletov and others in his group since the AGU presentation. Happy to post when and if there's input from them on the points made by other scientists gauging the long-term risk question. Witnessing a lot of emissions now is important information, and monitoring is essential in such regions. But drawing conclusions about overall risk from this is not possible unless setting those observations against both basic understanding of sub-sea permafrost response to ocean warming and what can be learned by looking back 8,000 years ago etc.
Andy Revkin, the feeling I got from reading your piece is that there is nothing to worry about WRT Arctic methane. Is this so?
You write for instance:
That’s the understatement of the year considering their conclusion that even under sustained heating, the brunt of the sub-sea methane won’t be affected in this millennium.
Just as it isn't about the entire Greenland and Antarctic ice sheets, but about how fast the amount of melted ice sheet needed to elevate sea level by 1-2 meters could come about, it isn't about the "brunt of the sub-sea methane" either.
If I've understood correctly, there could be about 1400 to 2200 billion tons of sub-sea methane (the estimates vary). In Shakhova et al. (2008) it is estimated that "release of up to 50 Gt of predicted amount of hydrate storage [is] highly possible for abrupt release at any time". That would increase the methane content of the planet's atmosphere by a factor of twelve. (source: Wikipedia)
50 Gt of 1400 Gt (lowest estimate) is 3.6%. Methane currently has a forcing of 0.5 W/m2 (if I've understood correctly).
I'm probably making some sort of mistake, but here goes:
So if 3.6% of the sub-sea methane would be released - hardly the "brunt" I would say -, this forcing would increase twelvefold to let's say 6 W/m2 (CO2 currently is 1.6 W/m2).
If this is correct, I'd be inclined to say 'Apocalypse perhaps not immediately but definitely not "Apocalypse not"'.
To correct my own stupidity: the impact of a forcing doesn't increase linearly, so 12 x 0.5 W/m2=6 W/m2 is too simple. Nevertheless, my question still stands. What happens when 2.5%-3.5% of the sub-sea methane stores gets released (the non-brunt, if you will)? How long/much warming would that take? Is there a correlation with Arctic sea ice?
Coincidentally global methane concentration started rising again in 2006, around the time when we saw the 'shift' in Arctic summer sea ice melt.
Neven - what you quote from wikipedia is from an EGU abstract, not a paper.
Thanks, Belette. Does that substantially alter the point of my question? Revkin talks about the brunt of sub-sea methane not gassing out this millennium. I figure just 2-3% would be enough to have a marked impact. Is that enough not to casually dismiss Arctic methane as a potential threat? Or is it 'Apocalypse not', like Revkin asserts?
I saw somewhere mention this might be methane from newly blooming bacteria in the surface layers. Don't forget the rise of slime, in other words.
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