(Originally posted elsewhere on ASIF, moved here by the author.)
There is a new review paper in Nature on the greenhouse gas flux from permafrost. ASLR mentioned it in passing on the previous page, but it deserves a bit more notice here.
Climate change and the permafrost carbon feedback
Abstract:
- Large quantities of organic carbon are stored in frozen soils (permafrost) within Arctic and sub-Arctic regions. A warming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change, but the magnitude and timing of greenhouse gas emission from these regions and their impact on climate change remain uncertain. Here we find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate and present a research strategy with which to target poorly understood aspects of permafrost carbon dynamics.
Press release from University of Alaska-Fairbanks here:
Scientists predict slower permafrost greenhouse gas emissions
My take -- permafrost is melting and degrading rapidly, and will continue to provide CO2 and CH4 to the atmosphere ... but at a modest rate, not in the form of a sudden "methane bomb". This should not be a surprise to most people here, as I think the evidence against a "bomb" scenario has been clear for some time (see Gavin Schmidt's comments last year).
Part of the problem of addressing the climate change issue is that its complexity does not readily lend itself to being addressed by the conventional reductionist scientific method that decision makers (& the public) have common to rely upon. Earth systems have multiple fat-tailed feedback mechanisms (which are currently dominated by positive rather than negative feedbacks); and while it is correct that science must use a reductionist approach to sub-divide these various mechanisms (which have different degrees of non-linearity, on different time-scales; with different initial & boundary conditions; and at different forcing rates & forcing magnitudes) in order to study them; unfortunately, to date the various climate change computer models have not been capable of adequately re-integrating all the synergistic (frequently non-linear) mechanisms. The US DOE has taken the lead in trying to re-integrate all of the reductionist inputs using Earth Systems Modeling, and which their state-of-the-art projections in CESM –High Resolution projections showed high climate sensitivity (see the third to last link at the end of this post), these preliminary findings (which did not rely on excessively high methane emissions) have been discounted as potentially being biased (due to uncertainties about non-linear responses) on the high-side (i.e. discounted for potentially erring on the side of greater drama).
Thus we are left with individual scientists and reporters discussing their reductionist finding (like a blind man describing an elephant to be snake like while he feels its trunk); and no one presenting a coherent reliable, timely, integrated overview (& I include the AR5 projections and Gavin Schmidt modeling efforts). A good example of this is the linked article by The Guardian focused on the recent Schuur et. al. (2015) paper (see second to last link at end of post), in which the researchers scale-back the rate of earlier (e.g. Schurr & Abbot, 2011) GHG emissions from permafrost degradation. While the reporter (Karl Mathiesen) entitles this article "Permafrost 'carbon bomb' may be more of a slow burn, say scientists"; he does have the grace to point at the end of his article to the even more recent Danish report by Hultman et al (2015) paper (see last link at end of this post) implies that the Schuur et al (2015) findings may be erring on the side of least drama (see extract below). However, even this caveat at the end of The Guardian article, Karl Mathiesen ignores multiple other factors that could work synergistically to accelerate GHG emissions from permafrost degradation, including: (1) Arctic Amplification, (2) the discontinuous nature of the permafrost (see:
http://innovations.coe.berkeley.edu/vol7-issue8-feb2014/studying-the-arctic-tundra.html), (3) invasion insect pests & invasion ground squirrel borrowing (see:
https://agu.confex.com/agu/fm14/meetingapp.cgi#Paper/20090), (4) degradation of boreal forest in the taiga (see:
http://news.mongabay.com/2014/0604-sutherland-taiga.html), (5) wildfires & reduced albedo associated with the shrub growth on the tundra (see:
http://onlinelibrary.wiley.com/doi/10.1111/gcb.12852/abstract), (6) penetration of warm surface water into the groundwater, (7) synergy between different soil microbes that have evolved to work together (see:
http://www.nature.com/ncomms/2014/140214/ncomms4212/full/ncomms4212.html), (
a reduction in the masking effect of Asian anthropogenic aerosols that could quickly double the current Arctic Amplification of two times the global mean surface temperature increase, (9) reductions in atmospheric hydroxyl ions resulting in longer residence times for methane, (10) probable future Arctic oil & gas development, (11) increasing sea level rise will flood more permafrost leading to more degradation (see:
http://onlinelibrary.wiley.com/doi/10.1002/2013JF002987/abstract), (12) the balance between CO₂ & CH4 emissions (see:
http://link.springer.com/article/10.1007%2Fs10533-014-0012-0#page-1), (13) photochemical oxidation (see:
http://www.sciencemag.org/content/345/6199/925) and (14) the influence of soil chemistry (see:
http://www.pnas.org/content/early/2014/04/02/1314641111).
http://www.theguardian.com/environment/2015/apr/09/arctic-carbon-bomb-may-never-happen-say-scientistsExtract: "The Danish study looked at several sites in Greenland and measured the amount of warming in the soil generated by microbial metabolism – the process that causes compost to generate its own heat. The amount of heat produced at sites with a lot of organic material in the soil, such as peat bogs, was 10 to 130 times higher than sites with more mineral soils.
“Results show that the impact of climate changes on natural organic soils can be accelerated by microbial heat production with crucial implications for the amounts of carbon being decomposed,” said the study. “Permafrost thawing in organic Arctic soils accelerated by ground heat production represent a potentially critical global-scale feedback on climate change.”
Gurney said this effect would be limited to regions further from the poles where the permafrost was warmer - allowing microbes to survive. He said it was in these areas that the extra warming from microbes could cause something approaching the carbon bomb effect. But the carbon contained in these regions was only a part of the total carbon stored in the permafrost.
“We are talking about a fraction, but not a tiny fraction. It is a considerable amount of carbon,” he said. “In Canada and the Yukon it might be around 20%.”"
R. Justin Small, Julio Bacmeister, David Bailey, Allison Baker, Stuart Bishop, Frank Bryan, Julie Caron, John Dennis, Peter Gent, Hsiao-ming Hsu, Markus Jochum, David Lawrence, Ernesto Muñoz, Pedro diNezio, Tim Scheitlin, Robert Tomas, Joseph Tribbia, Yu-heng Tseng, & Mariana Vertenstein, (December 2014), "A new synoptic scale resolving global climate simulation using the Community Earth System Model", JAMES, Volume 6, Issue 4, Pages 1065–1094, DOI: 10.1002/2014MS000363
http://onlinelibrary.wiley.com/enhanced/doi/10.1002/2014MS000363/E. A. G. Schuur, A. D. McGuire, C. Schädel, G. Grosse, J. W. Harden, D. J. Hayes, G. Hugelius, C. D. Koven, P. Kuhry, D. M. Lawrence, S. M. Natali, D. Olefeldt, V. E. Romanovsky, K. Schaefer, M. R. Turetsky, C. C. Treat & J. E. Vonk (09 April 2015), "Climate change and the permafrost carbon feedback", Nature, Volume: 520, Pages: 171–179, doi:10.1038/nature14338
http://www.nature.com/nature/journal/v480/n7375/full/480032a.htmlJ Hultman J, MP Waldrop, R Mackelprang, MM David, J McFarland, S Blazewicz, J Harden, MR Turetsky, AD McGuire, MB Shah, NC VerBerkmoes, L Lee, K Mavrommatis, and JK Jansson (2015), “Multi-Omics of Permafrost, Active Layer, and Thermokarst Bog Soil Microbiomes,” Nature, doi:10.1038/nature14238
http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature14238.html