Anthropogenic emissions of methane in the United States

TLDR

Regulating greenhouse gas emissions requires accurate methane source data, yet U.S. estimates may be biased by up to 50% and sectoral uncertainties are larger, despite California and Massachusetts targeting ~15% reductions by 2020. The authors analyze atmospheric methane measurements to constrain source estimates. Agricultural and fossil‑fuel extraction/processing emissions are likely at least twice as high as reported, complicating national and state reduction strategies that rely on accurate sectoral estimates.

Abstract

Significance Successful regulation of greenhouse gas emissions requires knowledge of current methane emission sources. Existing state regulations in California and Massachusetts require ∼15% greenhouse gas emissions reductions from current levels by 2020. However, government estimates for total US methane emissions may be biased by 50%, and estimates of individual source sectors are even more uncertain. This study uses atmospheric methane observations to reduce this level of uncertainty. We find greenhouse gas emissions from agriculture and fossil fuel extraction and processing (i.e., oil and/or natural gas) are likely a factor of two or greater than cited in existing studies. Effective national and state greenhouse gas reduction strategies may be difficult to develop without appropriate estimates of methane emissions from these source sectors.