Multi-model analysis of the radiative impacts of the 2022 Hunga eruption indicates a significant cooling contribution from the volcanic plume

Abstract. On January 15, 2022, the Hunga volcano eruption released unprecedented amounts of water vapor into the atmosphere alongside a modest amount of SO₂. In this work we analyse results from multiple Earth system models as part of the Hunga Tonga-Hunga Ha’apai Volcano Impact Model Observation Comparison Project.

Our results show a good model agreement over the climatic outcomes of the eruption, overall indicating a significant negative radiative forcing from the Hunga eruption. The multi-model mean of global instantaneous radiative forcing averaged over 2022–2023 is estimated at -0.19 ± 0.04 W/m² at the top-of-atmosphere (TOA), and -0.16 ± 0.03 W/m² at the surface. Simulations with free-running meteorology and climatological sea surface temperatures and sea ice yield a global mean TOA forcing of -0.14 ± 0.10 W/m² across two models for the first 2 years, decreasing to -0.09 ± 0.10 W/m² on average between 2022 and 2027. However, these global values may be underestimated by about 50 %, considering that recent SO₂ injection retrievals suggest nearly twice the amount than the 0.5 Tg-SO₂ used in the protocol. We also find that the contribution from added stratospheric water vapor is minimal and that the injected SO₂ and the resulting formation of stratospheric sulfate dominate the radiative forcing. However, water vapor played a key role in the initial aerosol growth, leading to a stronger negative radiative forcing during the first six months after the eruption compared to simulations without water vapor co-injection.