Methane Brain Drain
Ahhhhh.....methane. What could be a better topic for today? I wish I knew, because methane is one of the most difficult topics around when it comes to greenhouse gases. Well, first the good news. A new study, summarized here, finds that atmospheric methane has stabilized, possibly due to leak repairs at oil and gas pipelines and storage facilities and perhaps from reduced or slower growth of emissions from coal mining, natural gas production and rice paddies. Methane is also released into the atmosphere by a number of natural phenomena, such as biomass burning, volcanic eruptions and the melting of methane hydrates in permafrost. Oh, and it also results from cows - as Henry noted in a November 6th entry on his MeteoMadness blog.
The fact that methane is currently stable in the atmosphere is a good thing, but this entry at RealClimate.org makes it fairly clear that our understanding of methane variations is limited, to say the least. We simply can not use the data we have now to construct any sort of accurate forecast for future methane concentrations. Given that methane is a more potent (though shorter-lived) greenhouse gas than carbon dioxide, and given that methane in the atmosphere oxides into carbon dioxide, this is another area where more research is needed.
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As far as methane goes, it is also important to note that a significant amount of methane is stored in crystalline form on the deep ocean floor as methane hydrate, in an equilibrium condition that is very sensitive to pressure and temperature. If pressure drops or temperature rises more than just slightly, this methane reservoir will start to volatilize and seep back into the atmosphere, causing temperatures to rise.
Because of this, methane hydrate can serve as a negative feedback on ice ages when temperatures drop, more water is stored in ice caps, the oceans retreat, and pressure in the deep ocean decreases. The methane released because of the pressure drop serves to counter the cooling effect and stabilize temperature.
However, the same process of methane release from the deep oceans can also occur when temperatures rise. This methane release will *not* be a negative feedback on the warming, but rather a positive one, with the methane encouraging further warming that stimulates more methane release, causing a runaway warming effect. The release of methane hydrate is considered to be a strong candidate for causing the Eocene temperature spike about 55 million years ago, when global temperatures rose by a good 5-10�C in 10,000 years - a geologic blink of an eye.
This is a very interesting paper by David Archer, a Dept. of Geophysical Sciences Professor at the University of Chicago - rather technical, but well worth the read:
http://geosci.uchicago.edu/~archer/reprints/archer.ms.clathrates.pdf
Posted by Maria Helga Gudmundsdottir | November 26, 2006 7:39 PM