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.

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ORCID for P.A. Goodwin: orcid.org/0000-0002-2575-8948

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