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Methane, more scary than we thought

Methane’s Contribution to Global Warming Is Worse than You Thought

It seems we've been "fudging the numbers" in a sense, when comparing the global warming potential of methane to CO2. When global warming potential (GWP) of a gas is calculated, a time frame is assumed. The IPCC decided to use a 100 year time frame.

With a 100 year time frame methane heats up the planet 21 times as much as CO2. The problem with that assumption is that we don't have 100 years. A 20 year time frame would be much more realistic, given the urgency of climate crisis. With a 20 year time frame...

... any CH4 released today is at least 56 times more heat-trapping than a molecule of C02 also released today. And because of the way it reacts in the atmosphere, the number is probably even higher, according to research conducted by  Drew Shindell , a scientist at NASA’s Goddard Space Center. [emphasis mine]

 

What if we were to use the IPCC’s 20-year comparison instead of its 100-year comparison? For starters, it would force us to get much more serious about tackling  the sources of methane emissions. Here in the US, the top methane sources are the decomposition of wastes in landfills, agriculture (from ruminant digestion), and leaks from natural gas drilling and transmission. A new emphasis on methane would require us to get smarter about capturing methane at landfills, reduce the market incentives that encourage Americans’ meat-heavy diets, and ensure that methane isn’t leaking from fracking operations.

But beyond the policy specifics, adopting the 20-year global warming potential comparisons would be useful for changing how we think about climate change.

And we appear to be approaching some irrevocable tipping points that will create powerful negative feedback loops, the most worrisome being  the release of methane  stores at the bottom of the ocean and locked into sub-Arctic permafrost.

Image from Arctic Methane Release Tipping Point Diagram
With 56 times as much warming as CO2 in mind, we'd take this feedback more seriously.

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    Ruth Anthony-Gardner

    Preliminary findings from the current expedition to measure methane release in Laptev Sea aren't good.

    The findings come from an expedition now underway led by Professor Igor Semiletov, of Tomsk Polytechnic University, on the research vessel 'Academic M.A. Lavrentyev' which left Tiksi on 24 September on a 40 day mission. 

    The seeping of methane from the sea floor is greater than in previous research in the same area, notably carried out between 2011 and 2014. 

    'The area of spread of methane mega-emissions has significantly increased in comparison with the data obtained in the period from 2011 to 2014,' he said. 'These observations may indicate that the rate of degradation of underwater permafrost has increased.'

    The team are examining how the ice plug that has hitherto prevented the exit of huge reserves of gas hydrates has today 'sprung a leak'. [emphasis mine]

    Arctic methane gas emission 'significantly increased since 2014' - ...

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      Ruth Anthony-Gardner

      Methane release is ramping up on the East Siberian Shelf.

      Increasing Methane Releases in Arctic Proven by International Exped...

      "We reached and examined about 20 stations which had been measured earlier and each one showed the releases increasing. To underline that methane mega releases – with the area of over 1 km – are registered only at the East Siberian Shelf,” said ... Igor Semiletov.

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        Ruth Anthony-Gardner

        Update on East Siberian Arctic Shelf methane:

        1. Scientific Article - Current rates and mechanisms of subsea permafrost degradation in th...

        2. Easier-to-grasp interviews - Current rates and mechanisms of subsea permafrost degradation in th....

        The rate of subsea permafrost melt in the near-shore zone of the East Siberian Arctic Shelf has been measured. A "downward movement of the ice-bonded permafrost table of  about 14 cm/year over the past 31–32 years" means the melted layer is 14 cm deeper each year

        The bottom line is those reassuring studies saying methane dissolves out of rising bubbles and that methane hydrate deposits were overestimated are now irrelevant to an assessment of our danger.

        Shakhova and Semiletov found that 10% of the East Siberian Shelf are now hotspots, where methane release to the atmosphere is 3 to 5 orders of magnitude higher. Non-hotspot areas release 3 milligrams per square meter per day, while hotspot areas release 3,000 grammes per square meter per day. 

        This is exactly what is the difference between the linear and exponential. 

        Even if methane hydrate deposits don't explode, the way pingos have been doing on nearby land, a gigaton release could occur by growing hotspot areas. They measured the top of the undersea permafrost at zero degrees C. 

        The overriding issue is the vast majority of stored methane (99% if I read correctly) is stored as free gas under high pressure within deep sediments.

        Dr. Shakhova: The importance of hydrates involvement in methane emissions is overestimated. 

        ... the layer of hydrates composes just few hundred of meters – ... compared to thousands of meters of underlying gas-charged sediments in the ESAS.

        Dr. Semiletov ...the 5 billion tonnes of methane that is currently in the Earth’s atmosphere represents about one percent of the frozen methane hydrate store in the East Siberian Arctic Shelf. He finishes emphasising “…but we believe the hydrate pool is only a tiny fraction of the total.”

        So, only about 1% of the methane which warming could release from the ESAS will come from methane hydrate. The volume of methane-saturated sediment is gigantic.

        This huge area is 2 million square kilometres. The depth of this sedimentary drape is a few kilometres, up to 20 kilometres at places. 

        Unlike hydrates, this gas is preserved free; it is a pre-formed gas, ready to go. Over pressured, accumulated, looking for the pathway to go upwards.

        In our observations, we have accumulated the evidence that this gas front is propagating in the sediments.

        To me as a scientist, these points are enough to be convinced that methane release in the ESAS is related to disintegration of subsea permafrost and associated destabilisation of seabed deposits whether it is hydrates or free gas accumulations.

        Because the shelf area is very shallow (mean depth is less than 50 metres), a fraction of these emissions will reach the atmosphere. The problem is that this fraction would be enough to alter the climate on our planet drastically.

        Summing up:

        • The methane in our air at this time (5 billion tonnes) is about 1% of the amount stored as frozen methane hydrate in the East Siberian Arctic Shelf.
        • The methane in frozen hydrates is about 1% of the total stored methane, the remainder being gas under high pressure trapped in kilometers-deep sediment.
        • Free gas under pressure in sediment can create pathways for upward migration when undersea permafrost above it thaws, releasing to the air in hotspots. If hotspots continue to increase, as they have been seen to do from one expedition to the next, the release rates will increase exponentially. Even if water absorbs some of it, enough methane will likely escape to drastically alter the climate.
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