COVID-19 Emission Reductions Reveal the Efficiency and Warming Impact of Short-Lived Greenhouse Gases

JIANI YANG, Kazuyuki Miyazaki , Le Kuai, Kevin W. Bowman, Takashi Sekiya, Yuk Yung

The COVID-19 response provided a natural experiment to quantify the climate forcing efficiency of short-lived pollutants. Using satellite-constrained reanalysis and chemistry-climate simulations, we isolate the radiative impacts of anthropogenic NOₓ reductions through two modes: a rapid ozone decrease and a slower methane-driven adjustment that dominates the net effect. Globally, these responses produce a net radiative forcing of +17.87 ± 3.83 mW m⁻², indicating that methane-driven warming outweighs the initial ozone cooling. The rapid response is strongly regional: South and Southeast Asia (excluding China) contributes most by -2.96±0.78 mW m⁻² , driven by large emission reductions, efficient convective export, and high upper-tropospheric radiative sensitivity, with North and South America secondary. Because our experiment isolates the gas-phase NOₓ–O₃–OH–CH₄ pathway, it is an upper bound on the methane-mediated warming; co-reduced CO and volatile organic compounds and lower nitrate aerosol would offset part of it. NOₓ mitigation alone can cause delayed warming unless methane is concurrently controlled.