Global methane pledge versus carbon dioxide emission reduction

Abstract

Methane (CH4) is a potent greenhouse gas whose contribution to anthropogenic radiative forcing of the climate system is second only to carbon dioxide (CO2). CH4 emission reduction has become critical to global climate mitigation policy, resulting most notably in the global methane pledge (GMP), pledging a 30% reduction of CH4 emissions by 2030. Methane is, however, much shorter-lived in the atmosphere than CO2, so emissions reductions may have different impacts on global warming over time. We quantify the difference over time in global annual mean surface temperature of the GMP versus the equivalent amount of CO2 emission reduction. The avoidance of CH4 emissions in the 2020s due to the GMP initially results in greater relative cooling than the avoidance of the equivalent amount of CO2 emissions over the same period, but less relative cooling after ∼2060, when almost all CH4 emitted during the 2020s has been removed from the atmosphere but much of the CO2 emitted during the 2020s remains. However, if the GMP places the world on a lower CH4 emissions trajectory after 2030, this results in a persistently and substantially greater reduction to global warming than the equivalent change in the CO2 emissions trajectory, with a maximum difference of 0.22 ± 0.06 ∘C in 2055 and relative cooling for well over a century. This equates to a large difference in avoided climate change damages if momentum in CH4 emission reduction from the GMP can be sustained after the 2020s. While the greatest reduction in warming is obtained by reducing both CH4 and CO2 emissions, our results underscore the striking global societal benefits of sustained reduction in CH4 emissions.