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

On 15 January 2022, the Hunga Tonga-Hunga Ha'apai (HT) eruption injected SO2 and water into the middle stratosphere. The SO2 is rapidly converted to sulfate aerosols. The aerosol and water vapor anomalies have persisted in the Southern Hemisphere throughout 2022. 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 cool the 2022 Southern Hemisphere's average surface temperatures by less than 0.037°C. Plain Language Summary The Hunga Tonga-Hunga Ha'apai submarine volcanic eruption on 15 January 2022 produced aerosol and water vapor plumes in the stratosphere. These plumes have persisted mostly in the Southern Hemisphere throughout 2022. Enhanced tropospheric warming due to the added stratospheric water vapor is offset by the larger stratospheric aerosol attenuation of solar radiation. The change in the radiative flux could result in a very slight cooling in Southern Hemisphere surface temperatures.