The Estimated Climate Impact of the Hunga Tonga-Hunga Ha’apai Eruption Plume

On Jan. 15, 2022, the Hunga Tonga-Hunga Ha’apai (HT) eruption injected SO₂ and water into the middle stratosphere. The SO₂ rapidly converted to sulfate aerosols. The aerosol and water vapor anomalies observed by OMPS-LP and MLS, respectively, persisted in the Southern Hemisphere through 2022. The water vapor anomaly began to extensively move into the Northern Hemisphere in late 2022 above 28 km. The water vapor anomaly increases the net downward IR radiative flux whereas the aerosol layer reduces the direct solar forcing. The direct solar flux reduction is larger than the increased IR flux. Thus, the net tropospheric forcing will be negative. The changes in radiative forcing peak in July and August and diminish thereafter. Scaling to the observed cooling after the 1991 Pinatubo eruption, HT would reduce the 2022 Southern Hemisphere’s average surface temperatures by less than 0.05°C.