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An Arctic methane worst-case scenario

Filed under: — david @ 7 January 2012

Let’s suppose that the Arctic started to degas methane 100 times faster than it is today. I just made that number up trying to come up with a blow-the-doors-off surprise, something like the ozone hole. We ran the numbers to get an idea of how the climate impact of an Arctic Methane Nasty Surprise would stack up to that from Business-as-Usual rising CO2

Walter et al (2007) says that Arctic lakes are 10% of natural global emissions, or about 5% of total emissions. I believe that was considered to be remarkably high at the time but let’s take it as a given, and representing the Arctic as a whole. If the number of lakes or their bubbling intensity suddenly increased by a factor of 100, and it persisted this way for 100 years, it would come to about 200 Gton of carbon emission, which is on the same scale as our entire fossil fuel emission so far (300 Gton C), or roughly the amount of traditional reserves of natural gas (although I’m not sure where estimates are since fracking) or petroleum. It would be a whopper of a surprise.

Scaling Walter’s Arctic lake emission rates up by a factor of 100 would increase the overall emission rate, natural and anthropogenic, by about a factor of 5 from where it is today. The weak leverage is because the high latitudes are a small source today relative to tropical wetlands and anthropogenic sources, so they have to grow a lot before they make much difference to the sum of all sources.

The steady-state methane concentration in the air scales nearly linearly with the emission rate. Actually, the concentration goes up somewhat faster than a constant times the emission rate, because the lifetime in the atmosphere gets longer (IPCC TAR). Let’s err on the side of flamboyance (great word in this context) and say the concentration of methane in the air goes up by a factor of 10 for the duration of the extra methane emission (meaning that the lifetime doubles).

Using the modtran model on line I get a radiative forcing from 10 * atmospheric methane of 3.4 Watts/m2 (the difference in the instantaneous IR flux out, labeled Iout, between cases with and without 10x methane). Using the TAR estimates of radiative forcing gives 2.7 Watts/m2.

But methane is a reactive gas and its presence leads to other greenhouse forcings, like the water vapor it decomposes into. Hansen estimates the “efficacy” of methane radiative forcing to be 1.4 (Hansen et al, 2005, Shindell et al, 2009), so that puts us to 4 or even 5 Watts/m2.

This is about twice the radiative forcing today from all anthropogenic greenhouse gases today, or (again according to Modtran) it would translate to an equivalent CO2 at today’s methane concentration of about 750 ppm. That seems significant, for sure.

Or, trying to “correct” for the different lifetimes of the gases using Global Warming Potentials, over a 100-year time horizon (which still way under-represents the lifetime of the CO2), you get that the methane would be equivalent to increasing CO2 to about 500 ppm, lower than 750 because the CO2 forcing lasts longer than the methane, which the GWP calculation tries in its own myopic way to account for.

But the methane worst case does not suddenly spell the extinction of human life on Earth. It does not lead to a runaway greenhouse. The worst-case methane scenario stands comparable to what CO2 can do. What CO2 will do, under business-as-usual, not in a wild blow-the-doors-off unpleasant surprise, but just in the absence of any pleasant surprises (like emission controls). At worst comparable to CO2 except that CO2 lasts essentially forever.


  1. K.M. Walter, L.C. Smith, and F. Stuart Chapin, "Methane bubbling from northern lakes: present and future contributions to the global methane budget", Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 365, pp. 1657-1676, 2007.
  2. J. Hansen, "Efficacy of climate forcings", Journal of Geophysical Research, vol. 110, 2005.
  3. D.T. Shindell, G. Faluvegi, D.M. Koch, G.A. Schmidt, N. Unger, and S.E. Bauer, "Improved Attribution of Climate Forcing to Emissions", Science, vol. 326, pp. 716-718, 2009.

159 Responses to “An Arctic methane worst-case scenario”

  1. 151
    Lewis says:

    Andy – Agreed.
    As a response to the ‘worst-case’ present trajectory towards the feedbacks exceeding the sinks, forestry offers by far the best chance of a serious scale of Carbon Recovery, not least because of the incentives provided by its highly relevant product options.

    It could of course be done terribly badly, as a mere greenwash for BAU, with old forest clearances, land seizures and farmland conversion for foreign-owned exotic monoculture plantations, that earn ‘carbon credits’ for sale as a tax write-off to corporations with a PR problem. Given the limited suitable non-farmland available – last year’s WRI/WFN report identified 1.6GHa.s globally – and given the urgency of the climate and food-security problems, we simply cannot afford that ‘market-led’ outcome. For this reason the Carbon Recovery mode of geo-engineering clearly needs the formal UN supervision (noted previously) just as much as the more controversial Albedo Resoration mode.

    If a global afforestation program is done well, using mixed native species on appropriate land, with local rights of usage of thinnings and eventual annual growth increments, it would offer benign effects beyond the increase in terrestrial carbon sinks including the buffering of old-forest enclaves and biodiversity gains. One especially significant outcome could be the program’s function as a means by which all nations can verifyably recover their extant ‘carbon debt’ over an agreed period. (Reliable output records extend at least as far back as 1950). This undertaking could have a seminal effect on the climate treaty negotiations by helping to resolve the critically obstructive issue of ‘historical emissions’.

    Yet if the afforestation program were done really well it could produce far more than firewood, building poles and eventual lumber supplies, and it could sequester far more carbon too. The ancient and ongoing sylviculture of ‘coppice forestry,’ where deciduous trees are harvested young and regrown from the stump on a cycle of from 7 to ~28 years, offers gains including the growth of a very large root-ball supporting vigorous growth (about 20% better than cohort forestry), exceptional biodiversity (the highest of any European ecosystem), relatively low deadwood volumes minimizing fire-risk, better drought resistance, etc. The annual harvest averaging perhaps 10Ts dry wood /hectare globally could at optimum be converted to charcoal for use in farmland as both fertility enhancement and soil moisture regulator, in a modern version of the ancient ‘terra preta’ tradition. (This ‘Biochar’ option is showing results such that trials and operational usage are already under way in over twenty countries). With a moderately efficient charcoal retort converting ~35% by weight, 1.6GHa.s of coppice forestry should eventually yield perhaps 5.6GtC /yr, sequestering about 2.67ppmv of CO2. The inclusion of waste biomass from agriculture and conventional forestry could raise this amount substantially.

    A further aspect of the charcoal production is that around 28% of the feedstock’s energy content is provided as a crude syngas, which is readily convertable to methanol. (This will require modular ‘village scale’ plant to be developed rather than the present giant facilities that would require untenable feedstock transport). By my calculation 1.6GHa.s of coppice forestry could provide around 15Mbls/day of petrol-equivalent methanol. This is by no means the resolution of peak oil, but for those countries where liquid fuels are becoming unaffordable, this home production of charcoal and methanol may be the difference between utter collapse and a viable subsistence economy, not least by providing widespread full-term rural employment to help end the ruinous urban drift.

    The main limitation of such a forestry program is the lead-time it requires. Even with the incentives of improved farm yields and liquid fuel supplies, and with a Churchillian quality of program leadership, I doubt we’d see 1.6GHa.s planted in much less than 20 years, followed by say another 15 years to mature to full operation. This implies that substantial carbon sequestration and global farm yeilds support could start in the 2040s. While this cannot reliably control the present trajectory /worst-case scenario of the interactive feedbacks’ outputs exceeding the carbon sinks, it would certainly help to shorten the period that GHG pollution provides its destabilizing unnatural forcing of global temperature, and could thereby shorten the period for which Albedo Restoration would be required.


    Lewis Cleverdon

  2. 152
    wili says:

    “As far as I am aware average global temperature has never exceeded 25C except for very brief periods such as the PETM”

    And that is a guarantee that it could never happen in the future? Has this much carbon ever been spewed into the atmosphere at this furious rate before? Has the sun ever been this bright before? This is not your grandfather’s planet, much less the same planet as the PETM. I certainly hope we don’t get anywhere close to venusian runaway, but I don’t see how we can be 100% certain that it is an impossibility.

  3. 153

    #151–Lewis, I really like what you say here. Can you point to some sources for further study? Are there folks trying to make this happen?

    #152–wili, I think the best arguments against a Venusian-style runaway have been made here by Chris Colose and Ray Pierrehumbert, who have explained in detail why they believe it impossible. I won’t try to recap, as I am quite sure that if I do so off the top of my head, I will get it wrong!

    My take on it from a practical point of view is that it matters comparatively little, since the probable consequences of even 6 C are more than sufficiently severe to warrant putting a very high priority indeed on mitigating emissions. It’s like falling from 1000 meters, rather than ‘only’ 100–the former may be more spectacular, but it won’t kill you any more thoroughly.

    And in the ‘debate’, focus on the extreme but unlikely eventuality may even prove counterproductive, by ‘contaminating’ sound arguments with connotations of “pulp fiction” extremism. That’s not to say that any discussion of the topic should be embargoed, but I do think that over-focus on it is unlikely to be helpful.

  4. 154
    Hank Roberts says:

    > coppice forestry
    Plenty there going back decades. These programs are happening in China as well as the US, to my personal knowledge, and probably many other places.

    > wili … don’t see how we can be 100% certain
    That’s good. You’ve understood science can’t give you 100% certainty.
    That’s progress. Now, work with what IS possible from science.
    Nothing in life but religion and mathematics offers 100% certainties.

  5. 155

    Going back to methane worst case scenarios, I have posted 21 images of the Laptev Sea (Jan. 1-21, 2012) that come from the Danish Technical University website where images from satellites are updated daily. I am not sure, but these false-color images are from microwave sensors. I do not have scale although I have requested one.

    The black blobs (or “cornflakes” as termed by the MIT modelers in 2009) appear to be under the ice, because that area is covered with ice.

    Orange appears to be above the ice.

  6. 156
    ccpo says:

    #151–Lewis, I really like what you say here. Can you point to some sources for further study? Are there folks trying to make this happen?

    Comment by Kevin McKinney — 21 Jan 2012 @ 8:55 AM

    Coppice forestry, agro-forestry, reforestation, food forests/edible forest gardens…. these ways and more. None of this is new.





    Definitions: Farming

    (Note: Permaculture is a toolbox everything else above fits into.)

  7. 157

    Sorry, it is an unsophisticated blog. You will need to hit the page down key several times in order to arrive at the images.

  8. 158
    Hank Roberts says:

    Permafrost aerial mapping:

    “Here, we present the results of a pioneering ∼1,800 line-kilometer airborne electromagnetic survey that shows sediments deposited over the past ∼4 million years and the configuration of permafrost to depths of ∼100 meters in the Yukon Flats area near Fort Yukon, Alaska. The Yukon Flats is near the boundary between continuous permafrost to the north and discontinuous permafrost to the south, making it an important location for examining permafrost dynamics. Our results not only provide a detailed snapshot of the present-day configuration of permafrost, but they also expose previously unseen details about potential surface – groundwater connections and the thermal legacy of surface water features that has been recorded in the permafrost over the past ∼1,000 years….”

  9. 159
    wili says:

    Good work, hank. You can cut and paste others’ research. That’s progress. Now perhaps you can [edit: easy] stop demeaning earnest posters with your superior snide asides and deal with the actual threat at hand.