Methane story

[Stephen Salter]

Hi All

There is a story about excess methane and the interaction between
methane and sulphates at

http://www.timesonline.co.uk/tol/news/science/earth-environment/article6895907.ece

The source is Drew Shindell
http://www.sciencemag.org/cgi/reprint/326/5953/716.pdf

He argues that the ratio of emissions forcings of CO2 and methane are
1.6 and 0.99.

Stephen

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[John Nissen]

Hi Stephen,

Thanks for that.  Not having easy access to Shindell's paper, I found a good summary here:
http://www.nature.com/news/2009/091029/full/news.2009.1049.html

Note, for Manu et al., the methane effect is another example where IPCC is/was too conservative (read "absurdly optimistic"?).

The apparently wholly desirable ambition to reduce pollution could be a most deadly own-goal of environment policy, if the removal of sulphate aerosols (i.e. its cooling effect) outweighs the removal of carbon soot (i.e. its warming effect):

"The negative and positive effects of air pollutants must be taken seriously, says Almut Arneth of Lund University in Sweden, who also writes in Science this week². She says most assessments suggest that the cooling effect of sulphates at the moment outweighs the warming effect of black carbon. So legislating for the removal of air pollutants, particularly sulphates, would cause a rapid warming of the climate. "If we want to start developing really successful climate policies we've got to look at air pollution as well", she says."

This is an apparent dilemma.  However there is a solution: remove the sulphate and black carbon from the troposphere, but put a small proportion of the sulphate up into the stratosphere (where its SRM* cooling effect lasts for months/years rather than days/weeks).

BTW, would the methane rise into the stratosphere and zap the sulphate there?  That would be a big snag, especially if the methane emissions in the Arctic were to zap SRM efforts to cool the Arctic!

Cheers from Chiswick,

John

*SRM = solar radiation management

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[Andrew Lockley]

I think this research underestimates the problem.  Hydroxyl radicals will diminish if pollution rises (and not just from methane), driving higher GWP for methane as time goes on.  As far as I can tell, this ongoing, background reduction hasn't been incorporated into the model.  The effect they've highlighted therefore has the potential to get worse over time, and the GWP of methane will therefore rise inexorably.

Only with stable levels of hydroxyl radicals will the methane effect be as predicted.  Otherwise, the methane monster just keeps getting bigger.  

I've been trying to get some kind of context on this issue, and the metaphor that occurs to me is of a man being chased by a jack russell (CO2) and ignoring the bull charging at him (methane).

A

2009/10/30 John Nissen <j...@cloudworld.co.uk>