Tracking U.S. Liquefied Natural Gas Supply Chain Greenhouse Gas Emission Intensity through Direct Measurements

Recent regulatory and voluntary initiatives to estimate supply chain greenhouse gas (GHG) emission intensity of liquefied natural gas (LNG) have emphasized the use of direct measurements as activity-based national inventories tend to systematically underestimate GHG emission intensities. In this work, we demonstrate how measurement data can be integrated into a life cycle assessment (LCA) framework for assessing the GHG emissions of LNG supply chains by synthesizing results from a three year measurement campaign over 54 sites across production, midstream, and liquefaction stages. Measurement-informed GHG emission intensity ranges from 13.8 to 17.2 g of CO₂ equiv/MJ of LNG produced, about 19-39% higher than those derived from an activity-based inventory assessment. We also observe large variation in the contribution of each stage to the total supply chain emission intensity. Critically, we find that stages downstream of gas production account for up to 73% of the production to liquefaction GHG emission intensity of LNG. Thus, relying on aggregate production-only emission intensities as the basis to assess the emission impact of the LNG is likely to underestimate emissions, leading to potentially ineffective public or corporate policies. Finally, we find that supply-chain-specific GHG intensities can significantly differ from basin-level, representative GHG intensities; thus, assessments of the GHG intensity of LNG can benefit from being tied to individual transactions and specific gas pathways where data allow.