Upward revision of global fossil fuel methane emissions based on isotope database

A Corrigendum to this article was published on 15 February 2017

Abstract

Methane has the second-largest global radiative forcing impact of anthropogenic greenhouse gases after carbon dioxide, but our understanding of the global atmospheric methane budget is incomplete. The global fossil fuel industry (production and usage of natural gas, oil and coal) is thought to contribute 15 to 22 per cent of methane emissions1,2,3,4,5,6,7,8,9,10 to the total atmospheric methane budget11. However, questions remain regarding methane emission trends as a result of fossil fuel industrial activity and the contribution to total methane emissions of sources from the fossil fuel industry and from natural geological seepage12,13, which are often co-located. Here we re-evaluate the global methane budget and the contribution of the fossil fuel industry to methane emissions based on long-term global methane and methane carbon isotope records. We compile the largest isotopic methane source signature database so far, including fossil fuel, microbial and biomass-burning methane emission sources. We find that total fossil fuel methane emissions (fossil fuel industry plus natural geological seepage) are not increasing over time, but are 60 to 110 per cent greater than current estimates1,2,3,4,5,6,7,8,9,10 owing to large revisions in isotope source signatures. We show that this is consistent with the observed global latitudinal methane gradient. After accounting for natural geological methane seepage12,13, we find that methane emissions from natural gas, oil and coal production and their usage are 20 to 60 per cent greater than inventories1,2. Our findings imply a greater potential for the fossil fuel industry to mitigate anthropogenic climate forcing, but we also find that methane emissions from natural gas as a fraction of production have declined from approximately 8 per cent to approximately 2 per cent over the past three decades.

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Figure 1: Comparison of δ13CFF, δ13Cmic and δ13CBB source signatures from this study (red) and those used in 15 previous top-down studies (blue; see Supplementary Information section 8 for references).
Figure 2: Fossil fuel and microbial source CH4 budget terms.
Figure 3: Global FER long-term trend with mean values shown in solid black.

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Acknowledgements

We thank J. Randerson, K. Johnson, A. Cole, C. Itle, T. Wirth, T. Capehart, S. Montzka, and R. Klusman for comments and discussions. We acknowledge M. Schoell and A. Ionescu for contributing δ13Csource data. This research was supported by a National Research Council RAP fellowship and a CIRES IRP grant.

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Contributions

S.S. was responsible for study design, box-model development, analysis of TM5 results, manuscript preparation, and helped provide data. P.P.T. and J.B.M. helped with study design and improved the manuscript. O.A.S., G.E., E.J.D., S.E.M., V.A.A., B.H.V. and J.W.C.W. provided data and improved the manuscript. L.M.P.B. was responsible for TM5 modelling, helped with model analysis, and improved the manuscript.

Corresponding author

Correspondence to Stefan Schwietzke.

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The authors declare no competing financial interests.

Additional information

The reconstructed atmospheric global average δ13Catm data for 1984–1998 are from ref. 21 and global δ13Cice data are from ref. 24.

Reviewer Information

Nature thanks G. Allen, M. Heimann and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Supplementary information

Supplementary Information

This file contains a list of acronyms, the box-model descriptions, atmospheric measurements used, isotopic signature database details (data, explanations, and weighting schemes, paleo CH4 budget analysis, global latitudinal CH4 gradient simulations (TM5 model), and all sensitivity analyses. (PDF 2893 kb)

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Schwietzke, S., Sherwood, O., Bruhwiler, L. et al. Upward revision of global fossil fuel methane emissions based on isotope database. Nature 538, 88–91 (2016). https://doi.org/10.1038/nature19797

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