Going with what John Nissen just wrote earlier today on a different thread, it could possibly be very useful for policymaking, etc., and for those following this geoengineering group, to do something like the IPCC for future emission and mitigation scenarios, and construct a range of different 'Arctic event scenarios' for others to consider, involving methane, ice or both.
For me, I personally find something like the following arctic methane scenario quite astonishing to contemplate, and please note that it neither goes against anything said recently by David Archer at Real Climate, nor posits any mechanism that is not currently already activated towards change, and is entirely based upon already observed flux rates, conditions, etc. Let’s imagine that just a small fraction of the only the NON-HYDRATE C around the ESAS permafrost were released as methane rather quickly, either in one season, or even episodically over two or three years. Let’s make it just a mere .45%. This would be equal to 3 Gt methane. (3Gt CH4 = 2.3 Gt C, and 2.3 Gt C = ~.45% of 500Gt C, the amount estimated to be around the ESAS submarine permafrost [Shakhova, 2010]). This is a quite credible scenario. It is certain that there are already releases coming from this source, and that there is currently significant deterioration of the state of this carbon store from influxes of warming waters, lost ice, etc. Current methane fluxes recorded in the water column from around these hotspots are >1000x those expected from the observed atmospheric anomolies, so considerable methanotrophic activity could already be activated, making irregularities of microbial consumption capable of such a release. An estimated 3-5% of ESAS submarine permafrost is currently covered with taliks and degraded [Shakhova, 2010], and extrapolation from current hotspot releases would actually equal ~3.5Gt/yr [Shakhova, 2010]. A pulse of 3 Gt CH4 doubles the methane increase since industrialization: we have increased methane by about +157% (700ppb + 1100ppb= ~1800ppb), with abundances being ~1.9Gt (pre-industrial) + 3Gt = 4.9Gt CH4 (current). With best understanding of all indirect effects, this 3 Gt has added ~1W/m2. Thus, this modest methane pulse would add quite quickly about +62% to all the increased radiative forcing since industrialization. Further, spreading it over a couple of years wouldn’t make all that much difference: the feedback effect for methane is a ~ -.2 loss rate for each +1% of methane emission rate, which holds for up to about 33% increase in emission rate. (After that, I believe the negative loss rate increases further – does anyone know what happens after this?). Roughly, the release would constitute a ~+500% change, so the pulse should, I believe, last for something like double the lifetime, or more, something like two decades or more. In any case, it would last long enough that I suspect it might cause Much Ado. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
