Public Release: 

US methane emissions greater than thought, in recent years?

American Association for the Advancement of Science

Methane leakage from the U.S. oil and natural gas supply chain is greater than previously estimated, researchers report. U.S. oil and natural gas production has been growing steadily in the last decade. Although natural gas, in particular, releases less carbon dioxide than fossil fuels during combustion, the overall climate impact of natural gas also depends on how well plants and pipelines can corral leaky methane, which has a high global warming impact. By 2012 in the U.S., disagreement related to published estimates of methane emissions led to consensus that more data was needed. This spurred many studies to better characterize U.S. methane emission rates between 2012 and 2016. Here, Ramón Alvarez et al. integrated these measurements, many of which were captured in bottom-up (BU) approaches that quantify total facility-scale emissions (versus component-specific estimates), to provide an improved assessment of methane emissions from the oil and natural gas supply chain. Focusing on production regions accounting for about 30% of U.S. gas production, Alvarez and his team validated their BU emissions with a top-down (TD) approach involving aircraft, finding agreement across sites evaluated. Finally, the researchers scaled their facility-level findings to estimate leaks nationally, reporting that supply chain emissions in 2015, for example, were about 60% greater than estimates from the Environmental Protection Agency's Greenhouse Gas Inventory. This discrepancy is likely a result of existing inventory methods not capturing methane emissions that occur during abnormal operating conditions, like malfunctions, the authors say. Their results suggest paths for reducing methane emissions, including further research into causes of abnormal emissions.

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