Democratizing life cycle assessment by developing a streamlined model of greenhouse gas emissions from US natural gas supply chains

Summary: Natural gas (NG) supply chains contribute substantially to the global energy supply and anthropogenic methane emissions, making them frequent subjects of life cycle assessments (LCAs). To better characterize central tendencies and variability, we systematically reviewed and harmonized published estimates of life cycle greenhouse gas (GHG) emissions from United States NG supply chains. Results informed a streamlined LCA model (SLiNG-GHG: streamlined LCAs of NG-GHGs) that quantifies carbon dioxide and methane from three gates: transmission, distribution, and shipping. Median estimates employing harmonized emission inputs, are 10, 11, and 21 g CO2e/MJ gas (100-year global warming potentials [GWPs]), and 20, 22, and 33 g CO2e/MJ gas (20-year GWPs), delivered to each gate, respectively. Alternatively, inputting available, independent methane measurements, SLiNG-GHG estimates varied from −23% to +316% relative to baseline. Bottom-up inventories used in LCAs tend to underestimate methane compared with measurements. Results underscore the need for open-source, streamlined LCA models that can easily incorporate rapidly evolving measurements for non-experts like investors and regulators. Science for society: Natural gas is an important part of the current energy mix, yet uncertainty surrounding methane emissions is a challenge that needs to be addressed. Bottom-up inventories often underestimate emissions compared with direct measurements. This discrepancy can undermine market credibility and public trust in greenhouse gas (GHG) reporting. We address this challenge with SLiNG-GHG, a streamlined, open-source life cycle assessment model that makes emission analysis accessible to both experts and non-experts. The model development was grounded in data from a wide range of natural gas studies. We demonstrate the use of the model by integrating measurement datasets, bridging the gap between inventories and measurements. The model empowers policymakers, regulators, investors, and civilians to better evaluate natural gas emissions. The tool opens collaborative pathways across engineering, policy, and environmental science, enabling informed decision-making and better emission mitigation efforts.