Observational Constraints on the Global Methane Budget

The atmospheric burden of CH4 has increased by a factor of 2.5 since 1750, contributing 0.5 W m-2 to total radiative forcing by long-lived greenhouse gases (2.84 W m-2 in 2011), while its atmospheric chemistry affects background air quality and contributes an additional ~0.2 W m-2 indirect forcing through production of tropospheric O3 and stratospheric H2O. Because atmospheric CH4 has a relatively short life time, ~9 yr, reducing its emissions is considered a potential approach to slowing the rate of increasing radiative forcing. In fact, reductions in emissions from many anthropogenic sources would be cost-effective. But the effectiveness of emissions mitigation may be over-estimated by bottom-up inventories, so emission reductions must be verified through atmospheric observations. Also, reductions in anthropogenic emissions may be canceled by increased emissions from natural sources such as Arctic wetlands as they respond to changing climate.

NOAA has been measuring the global distribution of atmospheric CH4 since 1983. The data provide important constraints on methane’s global budget and how it is changing with time. An observed decrease in CH4 growth rate from 1983 to 2006 suggests that, if the CH4 lifetime has been approximately constant, then atmospheric CH4 is approaching steady state with no long-term trend in total global emissions through 2006. Super-imposed on this long-term picture is significant interannual variability in the CH4 growth rate, including an increasing atmospheric CH4 burden since 2007. Inherent in the spatial patterns of this variability is information about processes that emit or destroy CH4. In this presentation, I will review some key findings determined from NOAA CH4 measurements with particular focus on the renewed increase in atmospheric CH4 since 2007 and the potential contribution of climate feedbacks in the Arctic.


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Monday, May 13, 2013 - 3:30pm