All abuzz about methane [updated]

 

RealClimate tours the methane landscape, that greenhouse gas of renown, as a result of a number of recent papers describing increased release rates. Methane should be considered in context, and the risk it poses to additional warming tempered with realization that:

• While a physically powerful greenhouse gas, it does not have corresponding Earth blackbody radiation to absorb, and its absorption lines are narrow, at least compared to carbon dioxide and water (see chart below).
• The rate of increase of methane, even with these findings, is relatively small.
• It’s atmospheric lifetime (“residence time”, per ) is short, a 10 year lifetime, in contrast with carbon dioxide which has a 40% residence time of centuries, and a 20% atmospheric residence time of over 1000 years.
• When methane decays in atmosphere, it decays into carbon dioxide. 

To quote Professor David Archer’s summary from an earlier RealClimate post:

Could methane be a point of no return?

Actually, releasing CO₂ is a point of no return if anything is. The only way back to a natural climate in anything like our lifetimes would be to anthropogenically extract CO₂ from the atmosphere. The CO₂ that has been absorbed into the oceans would degas back to the atmosphere to some extent, so we’d have to clean that up too. And if hydrates or peats contributed some extra carbon into the mix, that would also have to be part of the bargain, like paying interest on a loan.

Conclusion

It’s the CO₂, friend.

(Figure credit above is from N Shakhova, I. Semiletov, I. Leifer, V. Sergienko, A. Salyuk, D. Kosmach, D. Chernykh, C. Stubbs, D. Nicolsky, V. Tumskoy, Ö. Gustafsson, “Ebullition and storm-induced methane release from the East Siberian Arctic Shelf”, Nature Geoscience (2013) http://dx.doi.org/10.1038/ngeo2007, 24 November 2013. Figure below is from Professor Kyle Forinash of the Physics Department, Indiana University Southeast.)

 

 

Addendum, Saturday, 28th June 2014

Professor Ray Pierrehumbert has taken a close look at the option of reducing other greenhouse gases besides carbon dioxide in order to mitigate climate change. There is some suggestion that reducing these may have a significant impact, and doing so may not have the same political opposition that going after CO₂ does. Nope. Quoting the above, but embellishing:

It’s STILL the CO₂, friend.