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Permafrost feedback update 2015: is it good or bad news?

Posted on 20 April 2015 by Andy Skuce

We have good reason to be concerned about the potential for nasty climate feedbacks from thawing permafrost in the Arctic. Consider:

  • The Arctic contains huge stores of plant matter in its frozen soils. Over one-third of all the carbon stored in all of the soils of the Earth are found in this region, which hosts just 15% of the planet's soil-covered area.
  • The Arctic is warming at twice the rate of the rest of the planet. The vegetable matter in the soils is being taken out of the northern freezer and placed on the global kitchen counter to decompose. Microbes will take full advantage of this exceptional dining opportunity and will convert part of these plant remains into carbon dioxide and methane.
  • These gases will add to the already enhanced greenhouse effect that caused the Arctic warming, providing a further boost to warming. There's plenty of scope for these emissions to cause significant climatic mischief: the amount of carbon in the permafrost is double the amount currently in the air. 

But exactly how bad will it be, and how quickly will it cause problems for us? Does the latest research bring good news or bad?

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.


There's a lot of information in this paper and, rather than attempt to describe it all in long form, I'll try to capture the main findings in bullet points. 

  • The top three metres of permafrost contain about 1035 PgC (billion tonnes of carbon). This is similar to previous estimates, but is now supported by ten times as many observations below the top 1 m depth. Very roughly, the deepest deposits richest in carbon are near the Russian, Alaskan and Canadian Arctic coasts, with the poorest in mountainous regions and in areas close to glaciers and the Greenland ice sheet.

The carbon content in the top three metres of permafrost soils. From Hugelius et al (2013).

  • The distribution of the carbon below 3 m depth is also now much better known. The main localities for this are shown in the map following. Three main types of deep permafrost carbon are identified: yedoma, river deltas and thick sediments.

From Schuur et al. (2015).

  • Yedoma deposits are perennially frozen deposits that consist of mostly ice (50-80%), along with organic matter. The estimates of carbon per unit volume have decreased by 22-55% compared to previous studies. The quantities of carbon are still uncertain with different studies producing estimates that range from 140 to 500 PgC.
  • The many major river deltas that feed into the Arctic Ocean deposit sediments rich in organic material that get frozen into permafrost. These contain about 91 PgC.
  • Other thick sediments outside the yedoma area contain 350-465 PgC.
  • The permafrost carbon quantity on shallow Arctic Ocean shelves (particularly the huge East Siberian Shelf) was not estimated.

Schuur et al. conclude:

Taken together, the known pool of terrestrial permafrost carbon in the northern permafrost zone is 1,330–1,580 Pg carbon, accounting for surface carbon as well as deep carbon in the yedoma region and river deltas, with the potential for ~400 Pg carbon in other deep terrestrial permafrost sediments that, along with an additional quantity of subsea permafrost carbon, still remains largely unquantified.

Decomposability experiments

Some permafrost soils have been incubated in controlled conditions in extended experiments lasting as long as twelve years to see how quickly they emit carbon dioxide and methane. Some key results:

  • The twelve-year incubation experiment showed that 50-75% of the original carbon was lost by aerobic processes (i.e., in the presence of oxygen) over that time.
  • The rate and nature of decomposition depends not only on temperature, but on the carbon and nitrogen contents of the soils and on the presence of water, which can starve the process of oxygen.
  • Anaerobic decomposition proceeds much more slowly than aerobic processes, producing methane as well as carbon dioxide. Although slower anaerobic decomposition emits only 3-7% of the carbon that aerobic processes do over a similar time period, the produced methane packs a bigger climatic punch. This means that the anaerobic processes have 25-45% of the impact over 100 years compared to a similar quantity of soil carbon exposed to aerobic decomposition.


For an extended summary of a permafrost carbon-cycle model, see the Skeptical Science article Modelling the permafrost carbon feedback (reference 48 in the graph below).


From Schuur et al. (2015)

  • The models predict emissions of 37-174 PgC by 2100, with an average of 92 PgC.
  • Not all of the models distinguished between carbon dioxide and methane. Estimates from expert assessments put methane emissions at 2.3% of the total carbon emissions, which would increase warming over 100 years by 35-48%.
  • The models assume permafrost carbon pools averaging 771 PgC, which is just over half the size of the Schuur et al. assessment of 1330-1480 PgC. This is partly due to the models mostly considering only the top 3 m of permafrost.
  • Over the next few decades, the increase in vegetation in permafrost ecosystems will take up more carbon than the amount released. Over longer time periods—and with increased warming—the plants will not be able to keep up and the Arctic will become a net source of carbon emissions.
  • According to the models, additional global warming caused by permafrost feedbacks will be 0.13-0.27°C.
  • Abrupt thaw mechanisms, such as thermokarst or rapid erosion are not modelled. The relative importance of these effects will depend on the local landscape, thermokarst being more important in lowlands and erosion more dominant in highlands and along coastlines. Many of these dynamic mechanisms will speed up carbon emissions, but some will slow them down. It's complicated and unravelling it will require more detailed models.

Subsea permafrost

There has been a large amount of public interest directed at the East Siberian Arctic Shelf, largely because of claims that the area could be the site of a ten-year 50 PgCH4 emission. This scenario has been widely criticized. Chris Colose summarized many of the arguments in his post Toward Improved Discussions of Methane & Climate. Schuur et al. appear to endorse this view:

Degradation of subsea permafrost from above by climate warming, and also from below by ongoing geothermal heat, will tend to increase new pathways between CH4 storage areas deeper in the sediments and the sea floor. But it is not known whether meaningful increases in CH4 emissions via these processes could occur within this century, or whether they are more likely to manifest over a century or over millennia. What is clear is that it would take thousands of years of methane emissions at the current rate [0.0017 PgCH4/year] to release the same quantity of methane (50 Pg) that was used in a modelled ten-year pulse to forecast tremendous global economic damage as a result of Arctic carbon release , making catastrophic impacts such as those appear highly unlikely.

Some additional observations:

  • Shallow shelves are where Arctic river deltas deposit carbon eroded from inland permafrost and they become hotspots for methane emissions to the atmosphere. 
  • Recently quoted methane fluxes from Arctic shelves are probably a result of improved observations of emissions that have been going on for many thousands of years since the end of the last ice age. 

The bottom line

Here are the main conclusions of Schuur et al.:

  • The pool of permafrost carbon is 1,300-1,580 PgC (1 Pg = 1 billion tonnes). This does not include additional amounts in other kinds of deep permafrost on land or permafrost on shallow ocean shelves.
  • During this century, 5-15% of the land permafrost carbon is vulnerable to release in the form of carbon dioxide or methane.
  • These emissions will be largest over the decades following thaw. They are likely to occur over decades and centuries to come.
  • Using a central figure of 10% for the portion of permafrost vulnerable this century yields a range of 130-160 PgC that could be emitted over the next several decades.
  • The Earth System models used in the latest IPCC assessment (AR5) did not incorporate permafrost carbon emissions.

How big of a deal is this?

Big numbers can be hard to grasp and it's easy to get lost among the PgCs, the TgCO2s and the GWPs. Let's assume that the permafrost emissions this century amount to 145 PgC (billion tonnes) of carbon. If these were all in the form of carbon dioxide, they would amount to 530 PgCO2. I will try to show in the comparisons below how significant these permafrost emissions might be. Note that these are my own calculations, comments and examples, not Schuur et al.'s. 

The 145 PgC emissions are for the RCP8.5, the worst-case human emissions scenario. Permafrost decomposition would be smaller at any given time in a less quickly warming world. For example, MacDougall et al (2012) found that emissions in 2100 under RCP2.6 (the aggressive mitigation scenario) would be ~40% of their estimate under RCP8.5. Applying this fraction to Schuur et al.'s estimate would yield 2100 emissions of about 60 PgC (220 PgCO2) under RCP2.6. This is a rough estimate for comparison purposes only and has not been calculated by Schuur et al.

1. The USA in 2013 emitted 5.2 billion tonnes of carbon dioxide from fossil-fuel combustion. Sustained over a century, such a rate of emissions would add up to match the emissions from the permafrost over the same timeframe. The permafrost feedback is almost as if we had conjured up a new USA, whose emissions would persist for a century or more. Admirers and detractors of America will surely agree, if only from a climate point of view, that one USA in the world is enough.

2. The established bitumen resource in the Athabasca oil sands is approximately 169 billion barrels. To produce all of this bitumen by the end of the century, would require rapid growth beyond even the industry's most ambitious plans. Swart and Weaver (2012) estimated that the total carbon in the established bitumen resource would be about 22 PgC. This is less than one-sixth the carbon expected to be emitted from permafrost over the same time frame. Canada is therefore likely to emit more CO2 from its share of the permafrost than would be produced even in a hell-for-leather exploitation of the oil sands.

3. The RCP2.6 pathway is the only one of the four modelled emissions scenarios that keeps warming below the 2°C target. The socio-economic model chosen to underpin this emission pathway (van Vuuren et al, 2011) relies heavily on carbon capture and storage (CCS) technology. In particular, a large deployment of bio-energy CCS (BECCS) is required for the latter half of the century, mostly to compensate for future natural gas and oil emissions that cannot be captured and sequestered. Deploying BECCS on this scale will pose problems for competing uses for agricultural land as well as for areas set aside for forest and wild-land preservation.

The top figure comes from van Vuuren et al (2011) and shows the primary energy sources for the RCP2.6 scenario. The lower figure (from a presentation by Andy Wiltshire) is based on the same model and shows the amount of BECCS negative emissions required after 2020 to stay under 2°C .

The amount of BECCS carbon sequestered in the century is 176 GtC, a little larger than the projected permafrost emissions under RCP8.5 and three times the estimated emissions under RCP2.6. Since permafrost emissions are not currently included in IPCC models, this means that—in order to preserve the same atmospheric greenhouse gas concentration profiles in the current RCP2.6 pathway—the amount of BECCS deployed would have to increase by one-third. An already very challenging mitigation strategy that relies on net negative emissions for the final decades of this century becomes even more difficult once permafrost feedbacks are considered.

4. The carbon budgets to limit our chances of avoiding 2°C look like this:

Carbon Tracker Initiative

Permafrost emissions this century of 60GtC/220GtCO2 (assuming slower thawing under an aggressive mitigation pathway) need to be subtracted from those remaining budget figures. Also, the graph above does not include the emissions from 2013 and 2014, which would subtract another roughly 20GtC/70GtCO2. This means that our budget from fossil fuels and land use changes needed to give us a good chance of avoiding dangerous climate change reduces from about 1000 GtCO2 to 700 GtCO2. The fraction of fossil fuel reserves that we have to leave in the ground just got significantly bigger.

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.

It is also a shame that important papers like this one are kept behind a publisher's paywall. The important policy decisions that need to be made to ensure a habitable planet require support from citizens informed with the latest and most reliable information. 

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Comments 1 to 23:

  1. The established bitumen resource in the Athabasca oil sands is approximately 169 billion barrels

    Small terminology nitpick: 'resource' should be 'reserve'. 'Resource' refers to the total amount of stuff present, 'reserve' is the portion that can potentially be mined. Wikipedia uses the terminology correctly.

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  2. "Reserves" definitions always imply commerciality. At today's commodity prices many undeveloped bitumen deposits may not be economically viable. Indeed, some oil sands development projects are currently being shelved.

    Here is the Society of Petroleum Engineers definition:

    RESERVES are those quantities of petroleum anticipated to be commercially recoverable by application of development projects to known accumulations from a given date forward under defined conditions. Reserves must further satisfy four criteria: they must be discovered, recoverable, commercial, and remaining (as of the evaluation date) based on the development project(s) applied. 

    Many commentators including Alberta's ERCB do refer to the established number as "reserves" (my emphasis)

    Established reserves—those reserves recoverable under current technology and present and anticipated economic conditions, specifically proved by drilling, testing, or production, plus that judgment portion of contiguous recoverable reserves that are interpreted to exist, from geological, geophysical or similar information, with reasonable certainty. 

    That was written a few years ago, before the oil price crash took many forecasters (especially the Alberta government) by surprise. It will be interesting to see if they downgrade their established reserves numbers in the face of the new reality.

    Until then, I will keep using "resource" for any undeveloped deposit that may or may not be commercial.

    It's worth noting also that in a recent paper by McGlade and Ekins in Nature, they used much lower numbers for Canada's reserves, although it is not completely clear to me what assumptions they used.

    [Comment updated]

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  3. Thanks for this great update, and especially for the very apropos final 'rant.' One point for now that I would love further clarification on:

    The second bullet-point under "The bottom line" section says:

    "During this century, 5-15% of the land permafrost is vulnerable to release in the form of carbon dioxide or methane."

    That seem rather low to me, given how rapidly the Arctic is warming. Are there uncertainty bars on the upper end that we're not seeing here? Does this assume a particular (perhaps optimistic?) emissions pathway?

    There is now a very wide range of possible increases in global temperature by the end of the century. How can the range of potential melt of permafrost be so relatively narrow?

    Also, is the low end of 5% pretty solid--that is, have we pretty well by now guaranteed that at least that much will thaw by the end of the century no matter what we do?

    Thanks ahead of time for any light you can throw on my (typical state of) bewilderment.

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  4. wili. thank you.

    Here's what the paper says, verbatim:

    Our expert judgement is that estimates made by independent approaches, including laboratory incubations, dynamic models, and expert assessment, seem to be converging on ~5%–15% of the terrestrial permafrost carbon pool being vulnerable to release in the form of greenhouse gases during this century under the current warming trajectory, with CO2-carbon comprising the majority of the release. There is uncertainty, but the vulnerable fraction does not appear to be twice as high or half as much as 5%–15%, based on this analysis.

    I should have added the word "carbon" after "permafrost (which I will now do). From their second sentence, I would expect that, while there is admitted uncertainty, the GHG release is very likely to be bigger than 2.5% in their judgement and likely bigger than 5%. The "current warming trajectory" that this is based on is something close to RCP8.5, so mitigation efforts could defer or cancel some of this, as well.

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  5. "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."  Another good reason to include these emissions: as a matter of policy they are largely beyond human control.  Based on new information (or, more likely, a long-delayed epiphany), the U.S. can always say "Oops, my bad" and cut its emissions dramatically.  But the 'permafrost U.S.' is doing no such thing.

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  6. Do these models incorporate the microbial heating of Hollesen et. al. (2015)?  paper here:

    Also, are these models including regional forcing feedbacks associated with ice-loss dynamics or do they simply look at radiative forcing parameters from the RCP runs?  If they do not include ice-loss albedo functions (as well as a 20% increase in regional temperature due to arctic surface algae growth) (carbon brief today: )  Then these models could be underrepresenting frozen soil feedbacks by over 300%

    We really need to get a handle on these regional feedback parameters under a potential arctic summer ice free condition within the next 10 years to be safe.

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  7. jja:

    The Hollesen paper was not cited by Schuur et al. 

    I would imagine that the models cited in this paper do take albedo changes into account since that's a rather basic effect, but I don't know for sure.

    Can you provide a reference or more reasoning for the 300% amplification?

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  8. Thanks Andy intersting but not sure we have a carbon budget really more of a debt and the permafrost melting is akin to interest on it.

    Ground water methane releases.

    More methanogensis bugs in the lakes as they warm and the lakes are full carbon for them to eat.

    When do the models melt the Arctic summer ice away in the paper by?

    Last CMIP5 RCP8.5run I’ve seen still had plenty of summer ice up to 2070, so presume that there might be a type 1 error model underestimation, given the way the arctic sea ice is melting already (can only get faster as we warm further and last 12 months have been the hottest in the temperature record, with an EL Nino just starting to brew), and most experts seem to suggest that an Arctic ice free summer by 2050 is inevitable at current rate of heating, and there is nothing we can do to slow the rate of heating by 2050, apart from geo-engineering and that is unlikely to be a safe bet.

    And melting the sea ice has been shown to accelerate Arctic warming.

    “We find that rapid sea ice loss forces a strong acceleration of Arctic land warming in CCSM3 (3.5-fold increase, peaking in autumn) which can trigger rapid degradation of currently warm permafrost and may increase the vulnerability of colder permafrost for subsequent degradation under continued warming.”

    (Lawrence 2008)

    Keep in mind that stopping burning fossil fuels will also stop the emissions of SO2 and that is providing a very significant cooling effect at present and thus when go warming increase markedly, as the CO2 levels wouldn't drop enough to slow warming even if all emissions stopped today for millennia.

    Atmospheric CO2 300ppm, sea levels 6-9m higher(LIG).

    CO2 350-400ppm, sea levels 20-25m higher (Early Pliocene), Arctic 14-19C hotter.

    CO2 400-450ppm, sea levels 30-40m higher (Miocene).

    We've emitted 500GtCO2, does anyone really think that the same can be released again and civilization can be safe (Whatever that means)?

    Not to mention ocean acidification and considering the changes already being witnessed.

    BECCS also needs to take into account the CO2 emissions from the cultivation of the biomass which some incidences can be higher than fossil fuel emissions if done poorly, (like taking tree brash and roots out forcing the soil respiring bugs to feast on old soil carbon), so no negative carbon, and CCS reduces power output significantly therefore you have burn more biomass to get the same output than without CCS.

    Scary that RCP2.6 is totally dependent on it!

    And can't help feeling climatic changes might make growing food alone, never mind extra biomass, more challenging in many places, like California say?

    Do we really have a carbon budget at all?

    Don't we need to get CO2 to 350ppm at least and adapt massively at the same time to new climatic systems the earth is heading for?

    Do we really have the luxury of being able to gamble anymore carbon emissions?

    A 50/50 chance at 450ppm of keeping warming to 2C by 2100, so that is akin to Russian Roulette with 3 bullets in the barrel, not sure why our policy makers are such brave gamblers considering the risks?

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    Moderator Response:

    [JH] Links activated.

    [AS] I hot-linked the Lawrence reference. The long URL was breaking the page

  9. Ranyl @ 8,

    "A 50/50 chance at 450ppm of keeping warming to 2C by 2100, so that is akin to Russian Roulette with 3 bullets in the barrel, not sure why our policy makers are such brave gamblers considering the risks?"

    The gamblers are gambling with consequences that otehrs will face. And they are able to round up popular support for getting away with damaging but cheaper ways of benefiting today because those unacceptable activities will only affect future generations, or people in other nations, or poeple who are not as fortunate.

    Such leaders are not gamblers at all. They are more like criminals since they actually have the ability to better understand what is going on yet they deliberately do not push for the action they can understand is required.

    Popularity and profitability fueled by successful deliberately misleading marketing is a fundamental problem that has been massively successful. I am hopeful that humanity can overcome the temptations. But it seems those temptations will not be overcome before massive irreparable damage occurs. The impacts of CO2 accummulation are going to be massive compared to the impacts of the accummulation of junk mortgages in the USA that led to the global economic catastrophe of 2008.

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  10. Thanks for the thoughtful reply and the context, Andy.

    The portion you quoted mentions "current warming trajectory" but you mention RCP. Are these really the same thing? Isn't the current warming trajectory (especially if they left out 2014) on the low end while we are actually on or above the ghg emissions trajectory laid out in RCP 8.5?

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  11. wili @10

    It's true that years prior to 2014 showed an emissions trend slightly above RCP8.5, but I think that the 2014 emissions figures give some hope that this tendency may be ending.

    My opinion is that it is wrong to characterize RCP8.5 as business-as-usual as some people have done. I think that more correctly it's an unlikely but still plausible worst-case scenario.

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  12. Thanks again, Andy. My impression is that RCP 8.5 was indeed _intended_ to represent a worst case scenario. But at least up to recently it has seemed more to reflect BAU. I will feel happier about the 2014 energy emissions figures when the actual atmospheric data start reflecting it. Just now weekly averages are in the 403 to 404 range...higher than they should be even under 'normal' rates of increase/acceleration. (I know, I know--warming Pacific and even local weather may be playing a role, and weekly bumps are to be expected...still a bit worrying, imho.)

    But I my basic question/confusion was whether a temperature trend is the same as an emissions trend. (Obviously, they will correspond over time, but it seems to me that over short periods, such as our current so-called 'hiatus,' they may diverge for a while.)

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  13. will - Temperatures are the result of all forcings (emissions including aerosols, land use, solar, volcanic) and internal cyclic and acyclic variations (ENSO, PDO, etc), modulated by thermal inertia and plain weather, so no, the shorter term temperature trend will not be exactly the emissions trend. Emissions are the dominant forcing change as per AGW, but far from the only one. 

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  14. Andy,

    Predicated on the idea that early arctic ice loss is not modeled under the scenario, that the albedo effects are underrepresented when they are included (due to algae bloom) and microbial heating effects are also not included then these emission profiles will be severely underrepresented.

    If summer arctic ice loss occurs within this decade as opposed to late 2040 as is currently being modeled, then this will allow microbial heat-driven decomposition to occur much more rapidly than modeled in Hollensen. 

    With a 3-meter depth decomposition profile establishing as early as 2060. 

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  15. Thanks again for a great article, Andy. I have a question:

    You state:

    • "The Arctic contains huge stores of plant matter in its frozen soils. Over one-third of all the carbon stored in all of the soils of the Earth are found in this region..." and
    • "the amount of carbon in the permafrost is double the amount currently in the air."

    Together, these would imply that carbon sequestered on land is 4-6 times the amount currently in the air. Do you have a reference for that estimate?

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  16. sailshrao: thanks.

    Those comments and figures came straight out of the Schuur paper, so that's my primary reference.

    However, this is from the AR5 Chapter 6 on the carbon cycle.

    The numbers in black are the pre-industrial carbon reservoirs measured in billion tonnes. The soil carbon is given as 1500-2400 and the atmospheric carbon as 589 billion tonnes. That gives a soil-atmosphere ratio of 2.5-4. That's lower than the ratio you calculated from the round numbers I cited (especially considering that the IPCC atmosphere numbers are pre-industrial). I would have to dig deeper to see where the discrepancy comes from.

    It looks to me that the IPCC estimate for the amount of carbon in soil could be wrong or out of date (or might not include permafrost soil, I don't know). Schuur et al's estimate for permafrost soils alone is 1330-1580 billion tonnes of carbon, which is bigger that the low IPCC estimate for all soil carbon and more than half of the IPCC upper estimate. If you look at both the Schuur and IPCC upper estimates, this implies that two-thirds of all soil carbon is in the Arctic, which can't be right.

    Let me start over again, with a big nod to HK's comment immediately below for pointing out what should have been obvious to me.

    The permafrost carbon reservoir ("underground" on the right-hand side) is 1700 billion tonnes, which is higher than Schuur et al.'s estimate of 1330-1580 billion tonnes, but when you include "the potential for ~400 Pg carbon in other deep terrestrial permafrost sediments" the numbers agree, more or less. So, according to the IPCC, 41-53% of all soil carbon is contained in permafrost. Most, but not all, permafrost is in the Arctic and boreal regions, so caution should be used in comparing IPCC numbers to the numbers from the Schuur paper, which confines itself to the Arctic and sub-Arctic.

    According to the IPCC diagram, the atmosphere in 2011 contained 829 billion tonnes of carbon, so that the ratio of soil to atmospheric carbon is approximately 4-5 to 1. The ratio of permafrost carbon to atmospheric carbon, according to IPCC numbers,  is about 2 to 1.


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  17. Andy:
    Your figure from IPCC has the permafrost carbon in a separate box to the right of the vegetation/soils box and is estimated as ~1700 Gt. That brings the total soil + permafrost carbon up to 3200-4100 Gt, or very roughly 4-5 times the present reservoir in the atmosphere (~850 Gt), not very different from saileshrao’s calculation. It also implies that the permafrost contains between 41% and 53% of all soil carbon.

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  18. Thank you, HK. I was looking for permafrost in the "north" of that figure and couldn't see it. It makes sense now. 

    Apologies to everyone for any confusion caused by me not seeing what's in front of my nose.  

    I have now updated my previous comment.

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  19. Andy,

    Thanks for the very informative article.

    Can I ask a question concerning the level of credence that is currently being given to the views of Peter Wadhams - and his colleagues on the Arctic Methane Emergency Group - as they pertain to this very topic? As far as I can tell from my (very) limited viewpoint, he seems to represent the more apocalyptic end of the clathrate release spectrum, with, perhaps, David Archer at the other. There was an SkS article about 2 years ago by Chris Colose which seemed to suggest this divergence in viewpoint, but I don't know if perspectives within the broad scientific community have changed much in the interim.

    I know that PW went very much out on a limb when he expressed the view that September levels of Arctic Sea Ice could be effectively gone by 2015. (He had elsewhere suggested the figure might be 2016 +/- 3 years, but, since we're in 2015, let's go with that version.) Not many people bought into this particular scenario, and, let's not be coy about this, it did provide a pretty soft target for the "it's not happening" brigade. The "official" AMEG line has softened (unsurprisingly) since PW made his claim back in 2012, and now simply states that...

    "The tipping point for the Arctic sea ice has already passed"

    However, and rather confusingly, about 2 lines further down on the AMEG home page, it goes on to state that...

    "The meltdown is accelerating and could become unstoppable as early as Sept 2015"

    Now, just because PW took an extreme view on Arctic Sea Ice, that doesn't necessarily brand him forevermore as "the boy who cried 'wolf!'" Hence my question about whether his views on methane release are still considered pretty extreme, or whether they're merely at the other end of a perfectly feasible probability range.

    Cheers    Bill F

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  20. Billthefrog, thanks.

    I can't speak to what the scientific community currently thinks about the imminent catastrophic release of methane from clathrates. I'm not part of the reseach community in this area and I can only rely upon what I read in the literature. The IPCC considers the risk by 2100 to be "very unlikely" (Chapter 12 Table 12.4 ).

    My own opinion, for what it is worth, is firmly with David Archer and Carolyn Ruppel. Of all the vulnerable stores in the Arctic clathrates, being deep in the ocean or deep below permafrost are, quite literally, the best insulated against future warming. Methane released from the ocean-floor clathrates, moreover, will tend to be consumed by bugs at the ocean floor or dissolved and oxidised in the seawater and will mostly not get into the atmosphere. (See Ruppel's excellent piece in Nature.)

    This does not mean that hydrates should not be a concern (even the IPCC with its "very unlikely" grants a 5-10% probability of this happening this century). Over longer terms, centuries and millennia, carbon release from hydrates will certainly provide  a big new source of carbon to the surface that will prolong and perhaps worsen the climatic effects of 20th and 21st Century human emissions.

    The persistence of the imminent clathrate bomb ideas seems to rely on the idea that there are huge metastable deposits of methane clathrates lying around very close to the surface on the East Siberian Arctic Shelf (ESAS). There is no evidence for the presence of these deposits either from sampling or geophysics. Furthermore, what we know about the physical chemistry of clathrates tells us that they should not exist at those depths and conditions.

    I will end by noting that in Shakhova et al.'s recent paper on methane release on the ESAS, the terms "hydrate"  is used only once, in a general sense in the body of the text and "clathrate" not at all. (i.e.,"Among Arctic reservoirs, subsea permafrost, hydrates, and associated CH4 deposits are the most worrisome owing to high heat transfer from rapidly warming shallow Arctic seas"). I have no idea why this is so: it could be that the authors themselves no longer think exposed hydrates on the ESAS are worthy of mention or if the reviewers of the paper insisted that shallow hydrates therenot be referred to without evidence that they exist. In any case, it is unlikely to be an oversight.

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  21. I wish there were some good news to report, but I would nonetheless urge everyone to read Robert McSweeney's latest piece at The Carbon Brief. He reports on a new paper in Nature Geoscience (which I have only so far skimmed, myself) that predicts that the terrestrial carbon sink will turn into a source by the end of the century, because the limited supply of nitrogen and phosphorous nutrients in soils will be insufficient to allow the increased plant growth from CO2 fertilization predicted in current Earth System models.

    If I have read the paper correctly (that's a big "if") a terrestrial carbon sink of 140 +/- 240 PgC assumed in current RCP8.5 models could instead turn into a net carbon source. (Note that the error bars are very large.)

    If so, that effect could be as big as--and additional to--the permafrost emissions reported above.

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  22. Thanks for informing us of this important study, Andy. Dare we hope for a main post on it soon?? '-)

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  23. First post from this non-scientist Andy - re. the recent Princeton paper -

    "New research led by Princeton University researchers and published in The ISME Journal in August suggests that, thanks to methane-hungry bacteria, the majority of Arctic soil might actually be able to absorb methane from the atmosphere rather than release it. Furthermore, that ability seems to become greater as temperatures rise." 

    This has been hailed in some quarters as the end of the "methane scare", because "the bugs will eat it all".

    The paper refers to "Arctic soils containing low carbon content — which make up 87 percent of the soil in permafrost regions globally". I suspect that the positive feedback from the other 13% of soil with higher carbon content may be greater than the negative feedback observed by this study, but what do I know?

    I have yet to see any feedback from scientists which supports my view, and meanwhile this paper is being used, and possibly abused, by the usual suspects.

    I would be grateful for your views.

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