Policy ForumEnergy and Environment

Methane Leaks from North American Natural Gas Systems

See allHide authors and affiliations

Science  14 Feb 2014:
Vol. 343, Issue 6172, pp. 733-735
DOI: 10.1126/science.1247045

You are currently viewing the figures only.

View Full Text

Log in to view the full text

Log in through your institution

Log in through your institution

  1. Inventories and emissions factors consistently underestimate actual measured CH4 emissions across scales.

    Ratios >1 indicate measured emissions are larger than expected from EFs or inventory. Main graph compares results to the EF or inventory estimate chosen by each study author. Inset compares results to regionally scaled common denominator (17), scaled to region of study and (in some cases) the sector under examination. Multiple points for each study correspond to different device classes or different cases measured in a single study. Definitions of error bar bounds vary between studies. (US, United States; Can, Canada; SC, South Central; Petrol. and Pet., petroleum; SoCAB, South Coast Air Basin; LA, Los Angeles; DJ, Denver-Julesberg; UT, Utah; HF, hydraulic fracturing). See SM for figure construction details.

  2. Potential contributions to total U.S. CH4 emissions above EPA estimates.

    EPA estimate in blue, based on central estimate and uncertainty range from large-scale studies from the inset in the first chart. Both NG sources and possible confounding sectors are included. NG production, petroleum production, and NG distribution emissions are based on regional empirical studies (1, 2, 6), which estimate emissions rates from high-emitting sources but do not estimate prevalence. Scenarios (a) to (c) correspond to 1, 10, and 25% of gas production or consumption from such high-emitting sources. Ranges (d) to (g) correspond to estimates for flowback emissions rates during hydraulic fracturing (HF) of all gas wells and shale gas wells, relative to EPA estimates. Ranges (h) to (m) reflect sources not included in EPA CH4 inventories but which could be mistaken for NG emissions by chemical or isotopic composition. See SM for details.