Evaluating net life-cycle greenhouse gas emissions intensities from gas and coal at varying methane leakage rates

Abstract

The net climate impact of gas and coal life-cycle emissions are highly dependent on methane leakage. Every molecule of methane leaked alters the climate advantage because methane warms the planet significantly more than CO2 over its decade-long lifetime. We find that global gas systems that leak over 4.7% of their methane (when considering a 20-year timeframe) or 7.6% (when considering a 100 year timeframe) are on par with life-cycle coal emissions from methane leaking coal mines. The net climate impact from coal is also influenced by SO2 emissions, which react to form sulfate aerosols that mask warming. We run scenarios that combine varying methane leakage rates from coal and gas with low to high SO2 emissions based on coal sulfur content, flue gas scrubber efficiency, and sulfate aerosol global warming potentials. The methane and SO2 co-emitted with CO2 alter the emissions parity between gas and coal. We estimate that a gas system leakage rate as low as 0.2% is on par with coal, assuming 1.5% sulfur coal that is scrubbed at a 90% efficiency with no coal mine methane when considering climate effects over a 20 year timeframe. Recent aerial measurement surveys of US oil and gas production basins find wide-ranging natural gas leak rates 0.65% to 66.2%, with similar leakage rates detected worldwide. These numerous super-emitting gas systems being detected globally underscore the need to accelerate methane emissions detection, accounting, and management practices to certify that gas assets are less emissions intensive than coal.