Multi-model effective radiative forcing of the 2020 sulphur cap for shipping

Abstract. New regulations of sulphur emissions from shipping were introduced in 2020, reducing emissions of SO₂ from international shipping by ~80 %. As SO₂ is an aerosol precursor, this drop in emission over the ocean will weaken the total aerosol effective radiative forcing (ERF) that historically has masked an uncertain fraction of the warming due to increased concentration of greenhouse gases in the atmosphere. Here, we use four global climate models and a chemistry transport model to calculate the ERF due to an 80 % reduction in SO₂ emissions from international shipping relative to 2019 emission estimates. The model means of the ERF range from 0.06 to 0.09 W m^-2 corresponding to the ERF due to the increase in CO₂ concentration over the last two to three years.