Bounding the climate viability of natural gas as a bridge fuel to displace coal

Natural gas has significant potential carbon benefits over coal when used for electricity generation, but these benefits can be offset by emissions of fugitive methane or delays in the adoption of near-zero carbon technologies. We analyze the time-evolution of radiative forcing from both natural gas and coal-based electricity generation by calculating average radiative forcing over an interval of time from greenhouse gas emissions under a range of assumptions for fugitive methane leakage, electricity generation efficiency, and delays in the adoption of near-zero carbon technologies. We find that leakage rates of between 5.2% and 9.9% are required for natural gas to result in greater mean forcing than coal over the next 100 years. We show that natural gas infrastructure with modest leakage could remain in place for 1.5–2.4 times the time interval that coal generation would have persisted prior to replacement with near-zero carbon technologies before the climate benefits of replacing coal with natural gas are negated. Natural gas can serve a viable bridge away from coal-based generation if avoiding longer-term climate impacts is prioritized, fugitive methane emissions are minimized, and the large-scale transition to near-zero carbon alternatives is unlikely to happen in the near-term. - Highlights: • Gas bridge fuel viability depends on leakage, efficiencies, and delays in near-zero carbon technology (NZCT). • With no NZCT delay, leakage rates could be 5.2%–9.9% for same 100-yr mean forcing. • At 2% leakage over a 100-yr forcing period, gas could be used 1.5–2.4 years per year of coal displaced. • A natural gas bridge is not a replacement for RPS and other policies to promote NZCT.