Update on my permafrost story. Last week I kind of stuck my neck out with a quite discouraging interpretation of information that has been made widely available about the future release of CO2 due to the melting of permafrost loaded with organic carbon. I spent much of the weekend looking to see if there could be more to the story, based on vetted scientific studies, and had some success. The best single source of information that I found was a study published in the journal Nature in 2015. It has strong authorship, made use of sources from 97 previous studies, and has since enjoyed widespread approval as expressed by numbers of citations and references. It is available in its entirety at the link below, and thankfully is quite readable if you are willing to take some time with it. Here I will mention just three of the main points of interest:
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1. Of 1.7 trillion tons of carbon held in permafrost soils about 1.035 trillion of this is held within the top ten feet, where its most likely source would have been plants that grew at the surface. The rest is made up of sediments that had been collected in other ways, often deposited at depth, quite rich, but difficult to evaluate with respect to future destiny. The surface carbon is of much more interest for making future projections.
2. Northern permafrost soils account for only 15% of global soil area. The other 85% is estimated to hold 2.05 trillion tons of organic carbon within its top ten feet from the surface. Very roughly, these numbers suggest that, over eons of time, permafrost formation accounted for the gaining of possibly 650 billion tons of carbon as compared with what that same soil would now hold if it had remained unfrozen. Scientists do not believe a similar amount is now subject to being released, but it is something to think about.
3. So how much can be released, and how fast? The authors of the study picked out eight models from their sources and compared them on a graph, which I have pulled out in a separate link, below. The models all differ in a number of ways. One of them is almost up to 400 Pg (same as billion tons) but over 300 years, mostly achieved in the second century out. Two models look for 150 Pg or more within the current century but then do not look further ahead, for some reason that is not revealed. Presumably they are leaving something on the table, perhaps substantial, for further investigation.
These numbers can easily be compared with the carbon budget, which is the tonnage of pure carbon (not CO2) that humans are allowed to emit in order to stay within 2.0C, lately considered to be around 250 tons under a suitable level of probability. In short, permafrost melting is not likely to steal all of our budget from us in this century, but could catch up with equivalent numbers in the next.
Using another perspective, each four billion tons of carbon emissions results in a gain of one ppm of CO2 in the atmosphere after allowing for 50% reduction via the usual activity of various sinks. On the Keeling curve that means the higher models show permafrost melting capable of adding up to 40 ppm in this century and 90 ppm by 2300. That is almost equal to the estimated decline in ppm between the mid-Pliocene, 4 million years ago, and the 280 level we knew back in 1800, which might be more than just a coincidence.
–Graph of eight model results: https://www.researchgate.net/figure/274698738_fig4_Figure-3-Model-estimates-of-potential-cumulative-carbon-release-from-thawing-permafrost
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Today’s new story picks:
An extract from Peter Brannen’s new book, “Ends of the World,” reprinted from the Guardian. The full book, which I have read and recommend, is loaded with information about Earth’s climate history over the last 700 million years, with a focus on causes of the major extinctions.
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The latest commentary from Amy Harder, posted on Axios. She always makes points that are timely and interesting
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A new message from pope Francis, who is a strong believer in what he hears from scientists. “If we don’t turn back, we will go down.” This pope is quite different from the ones at the time of Copernicus and Galileo.
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Nor should we ever neglect what Bill McKibben has to say:
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Finally, this is a lengthy new work from a pair of Australians who have been around this study for a long time, much like Bill McKibben, and know how to communicate just as effectively:
Carl