Non-CO2 Greenhouse Gases
Energy-related methane
Energy-related methane emissions are included in US-REGEN, with levels estimated as a function of upstream natural gas production and economy-wide distribution and use of natural gas as well as renewable and synthetic methane. Methane emissions rates per activity level for production and distribution are subject to measurement uncertainty but are assumed to decline over time with technological (and potentially regulation-driven) improvements in methane leakage and capture.
Methane emissions rates are calculated assuming an overall economy-wide leakage rate of 1.8% in the base year, declining at 2.5% per year. Upstream oil and gas production is assumed to account for 70% of base year emissions, while the remaining 30% is associated with pipeline gas delivery. The evolution of these drivers over time is used to scale future projected emissions, adjusted for an exogenously declining leakage rate. Mass-based leakage rates are connected to energy flows assuming 54 MMbtu per metric tonne of CH4, and methane emissions are translated to CO2 equivalent emissions using a global warming potential (GWP) of 25. Scenarios can be specified with a cap on total CO2 equivalent emissions to evaluate trade-offs between CO2 and methane reduction strategies.
Non-energy related GHGs
Other greenhouse gas emissions, including N2O, F-gases, and non-energy related emissions of methane, are not included in the current version of US-REGEN.