Permafrost Feedback Update 2015: Is It Good or Bad News?

Ted Schuur and sixteen other permafrost experts have just published a review paper in Nature: Climate change and the permafrost feedback (paywalled).  This long and authoritative article (7 pages of text, plus 97 references) provides a state-of-the-art update on the expected response of permafrost thawing to man-made climate change.  Much of the work reported on in this paper has been published since the 2013 IPCC AR5 report.  It covers new observations of permafrost thickness and carbon content, along with laboratory experiments on permafrost decomposition and the results of several modelling exercises.

The overall conclusion is that, although the permafrost feedback is unlikely to cause abrupt climate change in the near future, the feedback is going to make climate change worse over the second half of this century and beyond.  The emissions quantities are still uncertain, but the central estimate would be like adding an additional country with the unmitigated emissions the current size of the United States' for at least the rest of the century.  This will not cause a climate catastrophe by itself, but it will make preventing dangerous climate change that much more difficult.  As if it wasn't hard enough already.
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In summary, these projected permafrost emissions are a very big deal.  The Schuur et al. paper contains good news, in so far as an abrupt permafrost climate feedback is unlikely according to the experts, but the bad news is that the already difficult task of keeping warming under 2°C becomes much harder once we face up to the consequences of Arctic permafrost feedbacks.

Coda:  a short rant
It is a great pity that permafrost emissions estimates are not yet incorporated in all climate models.  Just because the emissions are uncertain does not mean that they should be excluded, after all, projections of fossil-fuel emissions are probably even more uncertain.

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