Over the last 10 years atmospheric methane levels have increased from about 1790 to about 1860 parts per billion (shown as nmol/mol in the plot above)---an increase of about 3%. In comparison atmospheric CO2 has increased from about 380 to 401 ppm over the last decade---an increase of about 5.5%. Since CO2 is about 200 times more abundant then CH4 and is accumulating more rapidly in the atmosphere, it might seem that theres not too much to worry about from the build-up of CH4 in the atmosphere. However, while methane is present in much lower concentrations in the atmosphere then CO2, it is a much more effective greenhouse gas ---- a molecule of CH4 captures about 20 times more heat then a molecule of CO2.
Much more attention has been focused on methods of Geoengineering CO2 removal from the atmosphere then CH4 removal for the simple reason that CO2 is responsible for most of the global warming occurring on the earth today. Also slowing down the development of ideas for geoengineering methane is the fact that there is no natural or "green" way to reduce methane concentrations in the atmosphere. To the best of my knowledge there is no major geologic or biologic processes that involves methane so its not possible to pump down CH4 by enhancing a natural process. I've discussed earlier in this blog that most of the geoengineering ideas for pumping down CO2 are based on idea to enhance natural processes ----this approach just won't work for methane.
Nonetheless, when Geoengineering of earth's climate eventually starts, it would be great if we could pump down CH4 at the same that CO2 is being removed from the atmosphere. Methane makes a significant contribution to global warming, and current CH4 levels are about 40% higher then pre-industrial CH4 concentrations in the atmosphere.
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