Turner, et al., reported in early 2016 that the global burden of atmospheric methane has been increasing over the past decade, but the causes are not well understood. National inventory estimates from the U.S. EPA indicate no significant trend in U.S. anthropogenic methane emissions from 2002 to present.
In this paper they use satellite retrievals and surface observations of atmospheric methane to suggest that U.S. methane emissions have increased by more than 30% over the 2002 to 2014 period. The trend is largest in the central part of the country, but we cannot readily attribute it to any specific source type. This large increase in U.S.methane emissions could account for 30 to 60% of the global growth of atmospheric methane seen in the past decade.
The U.S. has seen a 20% increase in oil and gas production and a ninefold increase in shale-gas production from 2002 to 2014, but the spatial pattern of the methane increase seen by GOSAT does not clearly point to these sources. More work is needed to attribute the observed increase to specific sources.
Others have found that the renewed growth in atmospheric methane between 2005 and 2010 could be explained by a 17 to 22% increase in global methane emissions. The authors suggest that increasing U.S. anthropogenic methane emissions could account for up to 30 to 60% of this global increase, but other studies have pointed to tropical sources as a major driver for this increase. Better understanding of U.S. anthropogenic methane emissions, particularly those from the livestock and oil and gas sectors, is obviously needed.
(The potential impact of methane release from melting gas hydrates in sediments within the shallow continental shelf resulting from warming seawater was not mentioned.)
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