title: Upward revision of global fossil fuel methane emissions based on isotope database.
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 emissions to the total atmospheric methane budget. 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 seepage, 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 estimates 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 seepage, we find that methane emissions from natural gas, oil and coal production and their usage are 20 to 60 per cent greater than inventories. 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.
authors.affiliation: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA.|NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, Colorado, USA.
authors.forename: Stefan
authors.initials: S
authors.lastname: Schwietzke
authors.affiliation: Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA.
authors.forename: Owen A
authors.initials: OA
authors.lastname: Sherwood
authors.affiliation: NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, Colorado, USA.
authors.forename: Lori M P
authors.initials: LM
authors.lastname: Bruhwiler
authors.affiliation: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA.|NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, Colorado, USA.
authors.forename: John B
authors.initials: JB
authors.lastname: Miller
authors.affiliation: Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma 2, Italy.|Faculty of Environmental Science and Engineering, Babes Bolyai University, Cluj-Napoca, Romania.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Etiope
authors.affiliation: NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, Colorado, USA.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Dlugokencky
authors.affiliation: Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA.
authors.forename: Sylvia Englund
authors.initials: SE
authors.lastname: Michel
authors.affiliation: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA.|NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, Colorado, USA.
authors.forename: Victoria A
authors.initials: VA
authors.lastname: Arling
authors.affiliation: Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA.
authors.forename: Bruce H
authors.initials: BH
authors.lastname: Vaughn
authors.affiliation: Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA.
authors.forename: James W C
authors.initials: JW
authors.lastname: White
authors.affiliation: NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, Colorado, USA.
authors.forename: Pieter P
authors.initials: PP
authors.lastname: Tans
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D002247:Carbon Isotopes / Q000032:analysis; D003031:Coal; D016208:Databases, Factual; D005579:Fossil Fuels; D008697:Methane / Q000032:analysis*; D009010:Monte Carlo Method; D059206:Natural Gas; D010578:Petroleum
chemical_list: D002247:Carbon Isotopes; D003031:Coal; D005579:Fossil Fuels; D059206:Natural Gas; D010578:Petroleum; D008697:Methane