Sunday, May 20, 2012

The potential impact of large abrupt release of methane in the Arctic

1. Methane’s Global Warming Potential (GWP)

The image displayed on the left shows that methane's global warming potential (GWP) is more than 130 times that of carbon dioxide over a period of ten years.

The image featured in a video and poster produced by Sam Carana1 (2012a).

IPCC2 figures were used to create the blue line. The red line is based on figures in a study by Shindell et al.3, which are higher as they include more effects. This study concludes that methane's GWP would likely be further increased when including ecosystem responses.

Ecosystem responses can be particularly strong in the Arctic. As mentioned on the poster, further warming in the Arctic can cause accelerated ice loss and trigger further releases of methane from sediments under the sea.

Release of methane from sediments is particularly worrying in areas such as the East Siberian Arctic Shelf (ESAS), where the sea is rather shallow (image below), causing much of the methane to enter the atmosphere without being oxidized in the water.

Furthermore, low water temperatures and long sea currents in the Arctic Ocean are not very friendly toward bacteria that might otherwise break down methane in the water.

2. Methane's Local Warming Potential (LWP) 

As said, release of methane from sediments is particularly worrying in the Arctic, where much of the water is rather shallow, as illustrated on the image below.

This is the case for areas such as the East Siberian Arctic Shelf (ESAS) that contain huge amounts of methane in the form of free gas in sediments and in hydrates.  

As said, Shindell's GWP figures do not include all indirect effects. Accelerated loss of sea ice and weakening of methane stores, due to the additional local warming of methane locally, can have a dramatic impact in case of large abrupt methane release in the Arctic.   

Such local warming can cause accelerated loss of the amount of snow and ice and of its capacity to reflect sunlight back into space, causing further warming, in a vicious circle of feedbacks.

The images below are from Flanner4 (2011) and shows that ice in the Arctic can cool areas by more than 30 Watts per square meter, and in summer by up to 70 Watts per square meter. 

Apart from decline of snow and ice, additional methane releases could also dramatically increase accelerate local warming.

The potential amount of methane estimated by Shakhova et al. are 1700 Gt5 in the ESAS (image left) alone, in the form of methane in hydrates and as free gas, with further carbon contained in permafrost that may be released as methane as the frozen soil and lakes melt. 

Some 50 Gt6 is ready for abrupt release at any time in the East Siberian Arctic Shelf area (ESAS) alone (image left, from Semiletov7, 2012).

The image below, from Sam Carana8 (2011), illustrates the danger of the situation in the Arctic, where high levels of greenhouse gases, combined with the impact of aerosols such as soot, can cause high summer temperature peaks.

High temperatures in the Arctic will speed up loss of sea ice, resulting in even further warming that weakens stores of methane in the form of hydrates and free gas in sediments under the water, in a vicious cycle that threatens to lead to runaway global warming. 

For more details on feedbacks, see extended version of this image and discussion at

3. Methane's Lifetime

The IPCC2 rates methane's Radiative Efficiency (in W m–2 ppb–1) at 3.7 x 10–4 and gives methane a perturbation lifetime of 12 years9. The IPCC9 defines perturbation time as the time it takes for a perturbation to be reduced to 37% of its initial amount. At the same time, the IPCC10 gives methane a global mean atmospheric lifetime of 8.4 years, which is the time it takes for half a perturbation to be broken down.

Methane's lifetime will be extended as the burden rises, due to hydroxyl depletion. The IPCC11  estimates that this methane feedback effect amplifies the climate forcing of an addition of methane to the current atmosphere by lengthening the perturbation lifetime relative to the global atmospheric lifetime of methane by a factor of 1.4.

A NASA12 (2009) article discussing Shindell's work mentions that increases in global methane emissions have caused a 26% decrease in hydroxyl. 

Prather et al.13 (2012) derive a present-day atmospheric lifetime for methane (CH4) of 9.1 years.

Methane is typically released gradually around the world, allowing much of the methane to be oxidized swiftly by hydroxyl in the tropics.

In case of large abrupt releases of methane in the Arctic, much of the methane may persist there for decades and thus amplify local warming dramatically. 

This is the case because the methane originated in one location, unlike other types of methane releases that occur gradually around the world. 

There is very little hydroxyl present in the Arctic atmosphere, as illustrated by the image left, from Taraborelli et al.14 (2012).  

The little bit of hydroxyl that is present in the Arctic atmosphere will soon be depleted in case of large abrupt releases.  

While the methane will eventually spread around the world, this will take time. Nesbit15 (2002) mentions that a major methane release in the high Arctic would take 15-40 years to spread to the South Pole. 

Abrupt releases in the Arctic could thus cause dramatic local warming, while lack of hydroxyl in the Arctic  could further make Arctic methane stay there for decades, with a high LWP, threatening to trigger further methane releases.

4. Abrupt release of 1Gt of methane in the Arctic

What would the impact be of abrupt release of 1Gt of methane in the Arctic, compared to the total global carbon dioxide emissions from fossil-fuel burning, cement manufacture, and gas flaring? The image below, from Sam Carana16 (2012b), gives a rather conservative impact, showing a rapid decline toward a small residual impact as carbon dioxide.

However, above graph does not include the indirect effect of triggering further releases. This is especially a threat in the Arctic, given the large presence of methane, the accelerated warming, the little oxidation that takes place in the Arctic atmosphere, and the time it will take for abruptly released methane to spread away from the Arctic.

The additional warming that this will cause in the Arctic will make the sea ice decline even more dramatically than is already the case now. The combined impact of sea ice loss and methane is huge, and threatens to trigger further releases of methane in the Arctic, with their joint impact accumulating as illustrated in the image below, also from Sam Carana16 (2012b).

Dramatic warming will first strike in the Arctic, but will soon spread, threatening to cause heatwaves and firestorms across North America and Siberia, adding additional soot and carbon dioxide in the atmosphere globally, as forests, peat bogs and tundras at higher latitudes burn, threatening to escalate in runaway global warming.


1. Sam Carana (2012a), Video and poster - methane in the Arctic

2. IPCC, Climate Change 2007: Working Group I: The Physical Science Basis, Table 2.14

3. Drew Shindell et al. (2009), Improved Attribution of Climate Forcing to Emissions.

4. M. G. Flanner et al. (2011), Radiative forcing and albedo feedback from the Northern Hemisphere cryosphere between 1979 and 2008.

5. Natalia Shakhova et al. (2010)
Presentation at SymposiumNovember 30, 2010

6. Natalia Shakhova et al. (2008)
EGU General Assembly 2008

7.  Semiletov et al. (2012)
On carbon transport and fate in the East Siberian Arctic land–shelf–atmosphere system

8. Sam Carana (2011), AMEG Poster at AGU 2011.

9. IPCC, Climate Change 2007: Working Group I: The Physical Science Basis, FAQ 10.3

10. IPCC, TAR (2001) Working Group I: The Scientific Basis, 4.1.1 Sources of Greenhouse Gases

11. IPCC, TAR, 04 (2001), Atmospheric Chemistry and Greenhouse Gases, Executive Summary

12. NASA (2009), Interactions with Aerosols Boost Warming Potential of Some Gases

13. Prather et al. (2012), Reactive greenhouse gas scenarios: Systematic exploration of uncertainties and the role of atmospheric chemistry

14. Taraborelli et al (2012),  Hydroxyl radical buffered by isoprene oxidation over tropical forests

15. Euan G. Nisbet (2002), Have sudden large releases of methane from geological reservoirs occurred since the Last Glacial Maximum, and could such releases occur again?

16. Sam Carana (2012b), How much time is there left to act?


  1. I'm wondering if anyone has computed the direct effect of having a "cloud" of CH4 overhead?

    The number that would be most helpful to me would be similar to the albedo ratio but indicating the ratio of outgoing radiation that could be expected to be reflected back towards earth for each increase of say 100 ppb of CH4. Not over any particular period of time, but for any time that the CH4 concentration was at that level.

    If we're concerned with how the Arctic ice is behaving during a particular melt season, and being cognizant of the fact that much of the radiative energy won't be measurable as sensible heat & may in fact be hidden in the following season's freeze, having a number that we can plug in indicating how much additional long wave radiation will be trapped because a cloud of CH4 is over an area might be helpful.

    Thanks in advance

    1. Hi Terry, the above post mentioned the paper by Shindell et al. which gives methane a global warming potential (GWP) of 105 over 20 years, while GWP would likely be further increased when including ecosystem responses. Methane releases in the Arctic are likely to cause further permafrost melting, in turn resulting in additional emissions. The post mentions methane's local warming potential (LWP) and points at local conditions that can further increase this potential. In the Arctic, huge amounts of methane are contained in the seabed, while much of the methane escaping from the seabed can enter the atmosphere relatively unaffected by methanotroph bacteria, due to shallow waters, cold waters and long sea currents, and while the methane that does enter the atmosphere will face relatively low levels of hydroxyl in the Arctic. Furthermore, river water can substantially warm up coastal waters. All this adds up to a high potential for methane in the Arctic to trigger abrupt methane releases from the seabed. Since warming in the Arctic is already accelerating due to numerous feedbacks, methane in the Arctic has a high potential to cause abrupt local warming (ALWP).

      Other types of methane releases (e.g. from wetlands, livestock, bio-waste and burning of fuel) occur spread out over the world throughout the year, i.e. such releases are pretty much global and continuous to start with. By contrast, as the post mentions, much of the methane from an abrupt release in the Arctic Ocean will initially remain concentrated over the Arctic Ocean, which covers only 2.8% of the Earth's surface. If 20% of the methane from an abrupt release over the Arctic Ocean still remains over the Arctic Ocean after 5 years (which could well be possible due to lack of hydroxyl in the Arctic), and using the above-mentioned GWP for methane of 105, then that methane will still have a LWP over the Arctic Ocean of 750 times the potency that the same mass of carbon dioxide has globally. Even higher figures than that are likely, since methane's GWP of 105 is for a time horizon of twenty years. Using a GWP for methane of 130 times that of carbon dioxide over a period of ten years would result in a LWP of 929 over 10 ten years. A methane cloud still hanging over the Arctic five years after its release will therefore have a LWP that is well over 1000 times the potency that the same mass of carbion dioxide has globally.

      There are further ways to express the potential of abrupt methane releases in the Arctic, such as their potential to trigger runaway local warming (RLWP), runaway global warming (RGWP), civilization destruction (CDP) and species extinction (SEP).