More methane madness

 

From "arctictransport":

Something strange

Posted on September 14, 2011 by rusfedmin

Commercial shipping through the Northeast Passage over the last couple weeks has reported the seas bubbling as if they were boiling.  Their observations have been reported to the science ministry who have sent scientists to investigate.

H/t Steve Bloom.

The image above is from "Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions" (Isaksen et al 2011). Although it sounds specialized, the paper, which is available in full, answers a number of basic beginner's questions about methane release (I needed to look those up . . . for a friend. Or for you, the reader. Yeah, that's it. For you the reader.)

1. How much methane is in the atmosphere now?


"The atmospheric concentrations in 2005 correspond to an atmospheric burden of 4,900 Tg CH4 (1 Tg = 1012 g)."


2. How long does it reside in the atmosphere?


"Atmospheric CH4 has a global average atmospheric lifetime of approximately 8 to 10 years [Denman et al., 2007]."


3. Why so brief, compared to CO2?

"Atmospheric CH4 is removed through oxidation by the hydroxyl radical (OH), mainly in the troposphere: R1    CH4 + OH --> H2O + CH3"


4. What is its ultimate fate?


Mostly to decay to CO2 (and ozone). So the best case scenario when you lose a ton of methane into the atmosphere is that it quickly oxidizes into a ton of CO2. Which, since it hangs around a lot longer and is the stuff that got us into this mess, is not so great.

5. There are only so many the hydroxyl radicals (OH) in the atmosphere. What happens if you release a bunch of it all at once?

It hangs around longer -- much longer -- leading to the amplified warming effect that gives the paper its title.

6. How much methane is in methyl hydrate deposits, compared to the atmosphere?

"The most recent review of the numerous published estimates of the amount of methane sequestered in global gas hydrate deposits converges on a range of 3 to 40 × 1015 m3 of methane [Boswell and Collett, 2011], which converts to a range of ∼1,600 to 21,000 Pg C."

1Pg = 1,000 Tg. So the amount of methane in the deposits is estimated to be between 300 times as much and 42,000 times as much as the total amount of methane in the atmosphere today.

7. Fuck me.

If any significant fraction of it escaped into the atmosphere on a human timescale, yes, that would be the general idea.

8. Could that happen? Really?

"Shakhova et al. [2008] speculate that 50 Pg CH4 could be released abruptly at any time from gas hydrates associated with subsea permafrost. Although there is no basis for estimating the rate of such a release, this value is used as a worst case scenario for the numerical model studies."

 9. Do they think such a release is likely?


No. "Although the high‐emission scenarios are unlikely to occur, they are compatible with the current knowledge of the cumulative magnitude of CH4 that might be emitted from permafrost thawing and from CH4 hydrate destabilization."

10. But worse case?

It's hard to call this the worst case, since what they are postulating is the release of less than 1% of the total reserves. But for the estimate they chose as a plausible worst case, 50 Pg, the short-term effect would be a global increase in radiative forcing of about 4W/m^2 (although, confusingly, they say 50 Pg could be released in one year, and then they model it as released over thirty years, significantly blunting the effect.)

The effect would be similar to doubling CO2 concentrations overnight. Temperatures would immediately rise, probably by 1-2C, with further rises in the following decades, depending on just what the actual climate sensitivity turns out to be.


Final thoughts from Iksaksen:

Fossil fuel CO2 emissions have increased substantially over the last decade and is now 40% higher than in 1990 [Le Quéré et al., 2009; Myhre et al., 2009]. The continued increase in greenhouse gas emissions toward the end of this century has the potential to produce significant warming at high northern latitudes well beyond what has been observed during the last decades [Hansen et al., 2007; IPCC, 2007]. There is a possibility that the Arctic temperature increases could be followed by extensive permafrost thawing, with enhanced CH4 emission from thermokarst lakes [Walter et al., 2006], with later release of CH4 from gas hydrates that would eventually be affected by warming temperatures. Considering the large, nonlinear atmospheric chemistry feedbacks discussed here, future CH4 emissions from permafrost deposits could be a larger concern for climate warming than previously thought.