title: Reconciling divergent estimates of oil and gas methane emissions.
abstract: Published estimates of methane emissions from atmospheric data (top-down approaches) exceed those from source-based inventories (bottom-up approaches), leading to conflicting claims about the climate implications of fuel switching from coal or petroleum to natural gas. Based on data from a coordinated campaign in the Barnett Shale oil and gas-producing region of Texas, we find that top-down and bottom-up estimates of both total and fossil methane emissions agree within statistical confidence intervals (relative differences are 10% for fossil methane and 0.1% for total methane). We reduced uncertainty in top-down estimates by using repeated mass balance measurements, as well as ethane as a fingerprint for source attribution. Similarly, our bottom-up estimate incorporates a more complete count of facilities than past inventories, which omitted a significant number of major sources, and more effectively accounts for the influence of large emission sources using a statistical estimator that integrates observations from multiple ground-based measurement datasets. Two percent of oil and gas facilities in the Barnett accounts for half of methane emissions at any given time, and high-emitting facilities appear to be spatiotemporally variable. Measured oil and gas methane emissions are 90% larger than estimates based on the US Environmental Protection Agency's Greenhouse Gas Inventory and correspond to 1.5% of natural gas production. This rate of methane loss increases the 20-y climate impacts of natural gas consumed in the region by roughly 50%.
authors.affiliation: Environmental Defense Fund, Austin, TX 78701;
authors.forename: Daniel
authors.initials: D
authors.lastname: Zavala-Araiza
authors.affiliation: Environmental Defense Fund, Austin, TX 78701;
authors.forename: David R
authors.initials: DR
authors.lastname: Lyon
authors.affiliation: Environmental Defense Fund, Austin, TX 78701;
authors.forename: Ramón A
authors.initials: RA
authors.lastname: Alvarez
authors.affiliation: Carbon Now Cast, LLC, State College, PA 16802;
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Davis
authors.affiliation: Environmental Defense Fund, Austin, TX 78701;
authors.forename: Robert
authors.initials: R
authors.lastname: Harriss
authors.affiliation: Aerodyne Research, Inc., Billerica, MA 01821;
authors.forename: Scott C
authors.initials: SC
authors.lastname: Herndon
authors.affiliation: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309; Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305;
authors.forename: Anna
authors.initials: A
authors.lastname: Karion
authors.affiliation: Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109;
authors.forename: Eric Adam
authors.initials: EA
authors.lastname: Kort
authors.affiliation: Department of Civil and Environmental Engineering, Washington State University, Pullman, WA 99163;
authors.forename: Brian K
authors.initials: BK
authors.lastname: Lamb
authors.affiliation: Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77004;
authors.forename: Xin
authors.initials: X
authors.lastname: Lan
authors.affiliation: Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523;
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Marchese
authors.affiliation: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544; pacala@princeton.edu shamburg@edf.org.
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Pacala
authors.affiliation: Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213;
authors.forename: Allen L
authors.initials: AL
authors.lastname: Robinson
authors.affiliation: Department of Chemistry, Purdue University, West Lafayette, IN 47907;
authors.forename: Paul B
authors.initials: PB
authors.lastname: Shepson
authors.affiliation: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309; Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305;
authors.forename: Colm
authors.initials: C
authors.lastname: Sweeney
authors.affiliation: Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77004;
authors.forename: Robert
authors.initials: R
authors.lastname: Talbot
authors.affiliation: Department of Geology, University of Cincinnati, Cincinnati, OH 45221.
authors.forename: Amy
authors.initials: A
authors.lastname: Townsend-Small
authors.affiliation: Aerodyne Research, Inc., Billerica, MA 01821;
authors.forename: Tara I
authors.initials: TI
authors.lastname: Yacovitch
authors.affiliation: Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523;
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Zimmerle
authors.affiliation: Environmental Defense Fund, Austin, TX 78701; pacala@princeton.edu shamburg@edf.org.
authors.forename: Steven P
authors.initials: SP
authors.lastname: Hamburg
keywords: Barnett Shale; greenhouse gas footprint; methane emissions; natural gas supply chain; oil and gas emissions