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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-131
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-131
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Ideas and perspectives 23 Apr 2019

Ideas and perspectives | 23 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Is Shale Gas a Major Driver of Recent Increase in Global Atmospheric Methane?

Robert W. Howarth Robert W. Howarth
  • Department of Ecology & Evolutionary Biology, Cornell University, Ithaca, NY 14853 USA

Abstract. Methane has been rising rapidly in the atmosphere over the past decade, contributing to global climate change. Unlike the late 20th Century when the rise in atmospheric methane was accompanied by an enrichment in the heavier carbon stable isotope (13C) of methane, methane in recent years has become more depleted in 13C. This depletion has been widely interpreted to indicate a primarily biogenic source for the increased methane. Here we show that the change may instead be associated with emissions from shale gas and shale oil development. While methane in conventional natural gas is enriched in 13C relative to the atmospheric mean, shale gas is depleted in 13C relative to this atmospheric level. Correcting for this difference, we conclude that emissions from shale gas production in North America over the past decade may well be the leading cause of the increased flux of methane to the atmosphere. Increased fluxes from biogenic sources such as animal agriculture and wetlands are far less important than indicated by some other recent papers using 13C data.

Robert W. Howarth
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Status: final response (author comments only)
Status: final response (author comments only)
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Robert W. Howarth
Robert W. Howarth
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Short summary
Atmospheric methane has risen rapidly since 2008, and has become less enriched in 13C, in contrast to the trend towards more 13C enrichment in the late 20th Century. Many have used this isotopic evidence to infer an increased biogenic source since 2008. Here I analyze the 13C trend with consideration that methane from shale gas is depleted in 13C compared to other fossil fuels. I conclude the rise in global methane since 2008 is driven primarily by fossil fuels, with shale gas a major source.
Atmospheric methane has risen rapidly since 2008, and has become less enriched in 13C, in...
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