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The Arctic Is Leaking Methane
registerShift and other readers sent in news that the Arctic Ocean seabed is leaking methane. "...climate experts familiar with the new research reported in Friday's issue of the journal Science that even though it does not suggest imminent climate catastrophe, it is important because of methane's role as a greenhouse gas. Although carbon dioxide is far more abundant and persistent in the atmosphere, ton for ton atmospheric methane traps at least 25 times as much heat. ... [One scientist] estimated that annual methane emissions from the East Siberian Arctic Shelf total about seven teragrams. (A teragram is 1.1 million tons.) By some estimates, global methane emissions total about 500 teragrams a year. ...about 40 percent is natural, including the decomposition of organic materials in wetlands and frozen wetlands like permafrost."
Uhhh, 1 teragram is 1,102,311.31 tons. How is that not 1.1 million tons? And how is that shoddy journalism again? Or are you pissed because they're not expressing it with the correct number of sigfigs or something?
It should be noted that 100-year global warming potential is around 23 -- the 20-year GWP is actually about 72. So the effects of permafrost thawing and possible release of any clathrate methane and the real warming impact in the short-term will be more extreme.
Having to worry about short tons vs long tons mean that the US system is bizarre.
So this is something like approximate to the largest natural gas tanker in the world releasing it's entire load into the air about 90 times over per year.
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Earth radiates at around 10 micrometers wavelength. As far as I can tell, methane has no absorption bands near there. So, why is it reckoned that methane is a potent greenhouse gas? Curious minds want to know.
Three responses come to mind:
1) Earth radiates across a range of wavelengths, not at a sharp 10 micron peak.
2) Methane is supposed to have 25x the radiative forcing of CO2 per unit mass. A methane molecule has a mass 16/44 that of carbon dioxide, so a kg of methane produces almost 3x the molecules produced by a kg of carbon dioxide.
3) A particular absorption peak or the peak emission wavelength doesn't matter. The important thing is the power change caused by the integral over all wavelengths of absorption multiplied by emission energy at each wavelength. Here that is for methane.
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From Linky:
Methane has a large effect for a brief period (a net lifetime of 8.4 years in the atmosphere)
Methane is a relatively potent greenhouse gas with a high 'global warming potential' of 72 (averaged over 20 years) or 25 (averaged over 100 years).
Global Warming Potential is a relative scale which compares the gas in question to that of the same mass of carbon dioxide (whose GWP is by convention equal to 1).
So methane is 70 times worse then CO2 over 20 years and 25 times worse over 100 years. Not exactly insignificant...
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