Climate impacts from water-rich large-magnitude volcanic eruptions
- Introduction
The January 2022 Hunga eruption was the most explosive volcanic event in the satellite era (Wright et al., 2022) and is providing a new paradigm for volcanic impacts on climate.
The shallow underwater setting of the eruption caused the volcanic impacts on climate to have a substantial component also from emitted water vapour, with stratospheric enhancement projected to remain in the stratosphere for 5-10 years (Millan et al., 2022).
The modest natural surface warming from the long-lived stratospheric water vapour is tangible within near-term climate projections (Jenkins et al., 2023), factored-in to the IPCC’s climate indicators analysis (Forster et al., 2023), adding to anthropogenic greenhouse gas warming and the 2023 shift into El Nino.
Figure 1: Hunga-Tonga signal within 28-year stratospheric water vapour anomaly timeseries (from MLS satellite measurements), and 20-year record of near-global stratospheric aerosol optical depth
From June 2023 WMO ozone bulletin (Steinbrecht, 2023; Millan et al. 2022) & Khaykin et al. (2022).
- The unusual volcanic forcing from the January 2022 Hunga eruption
The years after historical major volcanic eruptions such as 1991 Pinatubo and 1883 Krakatau have a substantial natural surface cooling from solar dimming from long-lived volcanic sulphate aerosol in the stratosphere, the magnitude of this volcanic forcing included within IPCC historical climate integrations.
The 2022 Hunga forcing is unusual compared to Pinatubo’s effects, with only a modest increase in stratospheric water vapour occurring in the years after the June 1991 eruption.
However, other historical major eruptions may have entrained external water into the volcanic plume (e.g. Rowell et al., 2022) and Joshi and Jones (2009) found Krakatau’s aerosol cooling was partially offset by a substantial surface warming from emitted water vapour, with similarities to Hunga’s forcing.
This PhD project will involve model experiments with the UK Earth System Model, to explore the climate influence from co-emitted water vapour in Krakatau-magnitude major eruption case studies.
The PhD is a co-operation with Met Office scientists, within the Leeds-Met Office academic partnership.
Figure 2 : Recent international multi-model papers have validated the UK model for Pinatubo aerosol (Quaglia et al., 2023), and background stratospheric aerosol conditions (Brodowsky et al., 2024).
- PhD aligns with new Hunga APARC activity & volcano-climate model experiments for CMIP7
The long-lived enhancement to stratospheric water vapour (Millan et al., 2022; Khaykin et al., 2022) has motivated a 2025 Hunga impacts report, aligned to the next WMO/UNEP Scientific Assessment of Ozone Depletion (see https://www.aparc-climate.org/activities/hunga-tonga/ ).
A landmark study currently in review on the longevity of the Hunga stratospheric water vapour (Jucker et al., 2023) indicates the surface warming effect may be strongest during 2025-2026, after the aerosol cooling effect has receded. Although the impacts from Hunga are relatively modest, compared to Pinatubo, the event has highlighted this new pathway for volcanic impacts on climate.
The unusual water vapour volcanic forcing has also motivated new multi-model experiments within the next phase of the VolMIP volcano-climate sub-group of CMIP7 (Zanchettin et al., 2016; 2022). The World Climate Programme has a co-ordinating “Explaining and Predicting Earth System Change” lighthouse activity (Findell et al., 2023), the Leeds supervisors playing a leading role also in the APARC international activity, and the 2025 Hunga impacts report.
- The PhD project
This PhD project will involve simulations with the UK Earth System Model (Sellar et al., 2019a, b), with new stratospheric water vapour volcanic forcing datasets to represent impacts from Hunga-like phreato-Plinian eruptions.
The Leeds team developed the interactive volcanic aerosol configuration of the UK composition-climate model UM-UKCA (Dhomse et al., 2020; Marshall et al., 2019; Dhomse et al., 2014) and the UKESM model experiments in the PhD will be designed to understand the progression of a scaled-up Hunga case study in preparedness for future major phreato-Plinian eruption.
The UKESM experiments will stem from satellite measurements of the Hunga aerosol and water vapour increase, and explore how volcano-climate impacts contrast with those from sulphur-dominated large-magnitude explosive eruptions such as 1991 Pinatubo. Exploring these new volcano-climate impacts gives the studentship potential for ground-breaking paper presenting Hunga-like major eruption impacts within near-term decadal climate projections.
The student will work under the supervision of Dr Graham Mann, Prof. Amanda Maycock and Dr Alex Rap, with advice also from Dr. Chris Smith (IPCC future climate projections) and Prof. Anna Hogg (Antarctic sea-ice impacts). With the PhD project a potential CASE studentship, the successful candidate will include a placement at the UK Met Office, to work alongside Dr. Johnson and Dr. Manners and others in the UKESM team based in Exeter.
References:
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Dhomse, S. S. , Mann, G. W., et al. (2020): “Evaluating the simulated radiative forcings, aerosol properties and stratospheric warmings from the 1963 Agung, 1982 El Chichón & 1991 Pinatubo volcanic aerosol clouds”, Atmos. Chem. Phys., 20, 13,627-13,654, https://doi.org/10.5194/acp-20-13627-2020
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