Benchmarking natural gas and coal-fired electricity generation in the United States

This study answers a critical question facing the energy sector in the United States: how does natural gas compare to coal as a climate change mitigation technique? Although natural gas burns cleaner than coal, methane leakage potentially undermines the climate benefits of fuel switching. This study investigates the impact of methane leakage using a novel plant-level lifecycle emissions inventory of greenhouse gas emissions associated with coal mining, transportation, and combustion at 337 existing coal power plants in the United States. Individual plant emissions rates ranged from 901 to more than 2,200 kgCO2e/MWh (100-yr GWP); generation-weighted average was 1,046 kgCO2e/MWh. Our study finds that the “breakeven” leakage rates for natural gas to have short and long term climate benefits over coal range from 4.4-20.9%, depending on the timeframe, plant efficiency, and upstream coal emissions. Emissions benefits can be maximized by replacing highest emitting coal plants with new natural gas plants. Finally, we find fugitive methane emissions can limit carbon reductions from natural gas carbon capture; above 2% leakage, methane leakage reduces CCS benefits by up to half for 20-yr GWP.