Residence time of Hunga stratospheric water vapour perturbation quantified at 9 years

Hunga Tonga eruption

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A return to ‘pre-Hunga’ conditions is expected around 2030, according to a paper by Zhou et al, which says: ‘Despite its critical importance for accurately predicting the near-term climate impact, estimating how long the Hunga-injected excess stratospheric water (HEW) will persist has been challenging.’ Various theories and claims have emerged (e.g. see this Talkshop post) since the eruption, concerning its potential and/or actual effects. The authors state: ‘Water vapour, as one of the most prominent greenhouse gases [1], can effectively alter radiative forcing and influence global surface temperature once it enters the stratosphere [2].’ An earlier study was said in a report to have found that ‘This underwater volcano’s impact has now been linked to measurable cooling across the Southern Hemisphere as well as other unusual atmospheric changes.’
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Abstract
The January 2022 eruption of the Hunga volcano (20°S) injected 150 Tg of water vapour into the middle atmosphere, leading to an increase in the stratospheric water burden of 10%, unprecedented in the observational record. In the first two years post eruption the stratospheric burden hardly changed, leaving the residence time of volcanically injected water vapour, a key control on its climate impact, uncertain. Here, using satellite observations, we show a substantial decline from 2024 to early 2025, the largest drop since the eruption. Comparison with 3-D numerical model simulations shows that the long-term removal of the Hunga water has now entered a new phase, with stratosphere-troposphere exchange playing an increasingly important role, exceeding Antarctic dehydration in 2024. We estimate that the additional stratospheric water vapour is now decaying steadily with an e-folding time of 3 years and will reach the observed pre-Hunga range of variability around 2030.
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Image: Hunga Tonga eruption