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CRISIS-FORUM  July 2012

CRISIS-FORUM July 2012

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Subject:

Re: Tropical forests spreading?

From:

Byron Smith <[log in to unmask]>

Reply-To:

Byron Smith <[log in to unmask]>

Date:

Mon, 16 Jul 2012 17:39:53 +0100

Content-Type:

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Compared to carbon dioxide (CO2), methane (CH4) has a relatively short atmospheric residency of something like 8-15 years (different sources seem to quote different numbers and some point out that the duration itself can change depending on concentration), after which time it oxidises into CO2. While it remains as CH4, it has a greenhouse forcing of something like 100 times that of CO2 molecule for molecule (again, sources differ, but the precise numbers aren't important here). Hence, the worst of its dirty work (from a climate perspective) is done during its few years as CH4, though it continues to be a problem as CO2 for a very long time. This means that, unlike CO2, the rate of CH4 release becomes critical to assessing its climate threat. A sudden pulse of a large amount of CH4 represents a grave danger. A long, slow release of a large amount represents little more danger than a long slow release of CO2 (which might still be a considerable threat, but on a longer timescale). There is indeed enough frozen methane in the Arctic vulnerable to warming to make a significant difference; the question is whether this may take the form of a sudden catastrophic release or a slow leak over decades/centuries, which will worsen our situation considerably, but not overwhelm anthropogenic emissions. In short, is Arctic methane a catastrophic game-changer with the potential to end civilisation almost overnight or a (non-unique) major headache making our path that much more difficult?

As I said, in assessing the threat from Arctic methane (permafrost and methane clathrates), likely rates of release are key. My sense of the situation (as a non-expert) is that current scientific understanding the mechanisms that contribute to frozen methane release suggests the latter is much more likely than the former, that is, we face a slow-leak major headache rather than a catastrophic spike with unspeakable consequences. Since I am no expert here, my grasp on the science could well be incorrect or incomplete. I am more than happy (or rather would be very unhappy, but out a desire for intellectual honesty would still be very much obliged) to be pointed to credible research demonstrating geophysical mechanisms capable of delivering catastrophic quantities of frozen methane on the brief timescales required for a massive spike.

The scientific sources suggesting a slow leak position have been mentioned a number of times on this forum. For those seeking bibliographies, David Archer has published numerous pieces both in the journals and at Real Climate with further references. Would someone be able to post credible peer-reviewed sources for the catastrophic spike suggestion?

Regards,
Byron Smith

PhD candidate
University of Edinburgh

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