Climate impacts from water-rich large-magnitude volcanic eruptions

Year
2026
Primary Supervisor
Graham Mann <[email protected]>
Institution
University of Leeds (School of Earth and Environment)
Possibility of becoming a CASE project
Yes
Collaborative Project
Yes
Academic Supervisors
Alex Rap <[email protected]> (University of Leeds, School of Earth and Environment), Amanda Maycock <[email protected]> (University of Leeds, School of Earth and Environment)
Research Themes
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Project Partners
Ben Johnson <[email protected]> (UK Meteorological Office, Earth System Science), James Manners <[email protected]> (UK Meteorological Office, Weather science)
Research Keywords
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Relevant Degree Courses
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1. 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 Hunga eruption caused its radiative forcing to have a substantial component also from emitted water vapour (Sellitto et al., 2022), with stratospheric enhancement projected to remain in the stratosphere for 5-10 years (Millan et al., 2022).

The high altitude of the stratospheric water vapour layer (above 20km) is now known to have caused only a weak surface effect, much less than the solar dimming effect from the volcanic aerosol (Schoeberl et al., 2023, 2024 ). However, a follow-on study (Wang and Huang, 2024) has demonstrated how a future eruption’s emitting closer to the tropopause would cause a substantial volcanic H2O vapour surface warming effect.

Another model study (Jucker et al., 2024) finds the long-lived Hunga stratospheric water vapour causes later warming effect and Wu et al. (2025) show how Hunga released 18.8Tg of SO2, the underwater setting removing 95% of emitted sulphur, only 5% within the eruption plume reaching the stratosphere. Hunga’s elevated global stratospheric optical depth was the largest since Pinatubo, and the reduction to background levels represents a natural warming trend alongside the concurrent 2023 shift into El Nino.

Hunga strat-h2o & strat-aerosol increase
Figure 1: Hunga-Tonga clearly apparent within a) 28-year stratospheric water vapour anomaly timeseries from MLS satellite measurements, and b) 20-year satellite record of near-global stratospheric AOD. From June 2023 World Meteorological Organisation ozone bulletin (Steinbrecht, 2023) and Khaykin et al. (2022).

2. 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 a 2- or 3-year solar dimming caused by long-lived volcanic sulphate aerosol in the stratosphere. In the years after such major eruptions, decadal forcing trends become dominated by natural radiative forcings, with a sudden-onset into strong surface cooling.  Time-varying global volcanic aerosol datasets for historical major eruptions are a key input dataset into for example IPCC 1850-present climate model integrations.

The 2022 Hunga forcing is unusual compared to Pinatubo, a much smaller increase in stratospheric water vapour occurring in the years after the June 1991 eruption. However, other historical major eruptions 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.

Model predicts key uncertainty of particle size distribution.
Figure 2 : Recent international multi-model papers have validated the UK model’s predicted particle size variation for Pinatubo aerosol (Quaglia et al., 2023), and background stratospheric aerosol conditions (Brodowsky et al., 2024).

3. PhD aligns with 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/ ).

The first study to assess the longevity of the Hunga stratospheric water vapour (Jucker et al., 2023) identified the surface warming effect would be strongest during 2025-2026, after the aerosol cooling effect has receded.  Although the climate impacts from Hunga are only weak, the event has highlighted the potential for stratospheric water vapour forcing within 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, to be released in December 2025, during AGU conference week.

4. The PhD project

This PhD project will involve simulations with the UK Earth System Model (Sellar et al., 2019a, 2019b), with new stratospheric water vapour volcanic forcing datasets to represent impacts from Hunga-like water-rich major 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 water-rich 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 project is supervised by 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:

Brodowsky, C., Sukhodolov, T., Chiodo, G. et al. (2024): “Analysis of the global atmospheric background sulfur budget in a multi-model framework”, Atmos. Chem. Phys., vol. 24, 5,513–5,548 , https://doi.org/10.5194/egusphere-2023-1655 .

Dhomse, S. S., Emmerson, K. M., Mann, G. W. et al. (2014): “Aerosol microphysics simulations of the 1991 Mt Pinatubo eruption with UKCA composition-climate model”, Atmos. Chem. Phys., vol. 14, 11,221–11,246, https://doi.org/10.5194/acp-14-11221-2014.

Dhomse, S. S. , Mann, G. W., Antuña Marrero, J.-C. 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., vol. 20, 13,627-13,654, https://doi.org/10.5194/acp-20-13627-2020

Findell, K., Sutton, R., Caltabiano, N. et al. (2023): “Explaining and Predicting Earth System Change: A World Climate Research Programme Call to Action”, Bulletin of the American Meteorological Society, E325-E339, https://doi.org/10.1175/BAMS-D-21-0280.1 .

Joshi, M. M. and Jones, G. S. (2009): “The climate effects the direct injection of water vapour into the stratosphere by large volcanic eruptions“, Atmos. Chem. Phys., vol. 9, 6109–6118, https://doi.org/10.5194/acp-9-6109-2009 .

Jucker, M., Lucas, C. and Dutta, D. (2024): “Long-term surface impact of Hunga Tonga-Hunga Ha’apai-like stratospheric H2O injection”, J. Climate, vol. 37, 4507-4521, https://doi.org/10.1175/JCLI-D-23-0437.1 .

Khaykin, S., Podglajen, A., Ploeger, F. et al. (2022): “Global perturbation of stratospheric water & aerosol burden by Hunga Tonga eruption”, Comms Earth & Env., vol. 3:316, 1-15, | https://doi.org/10.1038/s43247-022-00652-x

Mann, G. W., Dhomse, S. S., Deshler, T. et al. (2015), “Evolving particle size is the key to improved volcanic forcings”, Past Global Change, vol. 23, no. 2, 52-53, https://doi.org/10.22498/pages.23.2.52 .

Marshall, L. A., Johnson, J. S., Mann, G. W. et al. (2019): “Exploring how eruption source parameters affect volcanic radiative forcing using statistical emulation”, J. Geophys. Res. Atmos., vol. 124, 964-985, https://doi.org/10.1029/2018JD028675 .

Millan, L., Santee, M. L., Lambert, A. et al, (2022): “The Hunga Tonga-Hunga Ha’apai Hydration of the stratosphere”, Geophys. Res. Lett., e2022GL099381, https://doi.org/10.1029/2022GL099381 .

Quaglia, I., Timmreck, C., Niemeier, U. et al. “Interactive stratospheric aerosol models’ response to different amounts and altitudes of SO2 injection during the 1991 Pinatubo eruption”, Atmos. Chem. Phys., vol. 23, 921–948, 2023, https://doi.org/10.5194/acp-23-921-2023 .

Rowell, C., Jellinek, A. M., Hajimirza, S. et al. (2022): “External surface water influence on explosive eruption dynamics, with implications for stratospheric sulfur delivery and volcano-climate feedback”, Frontiers Earth Sci. vol. 10, 788294, 1-39, http://doi.org/10.3389/feart.2022.788294 .

Schoeberl, M. R., Wang, Y., Ueyama, R. et al. (2023): “The estimated climate impact of the Hunga Tonga-Hunga Ha’apai eruption plume”, Geophys. Res. Lett., vol. 50, e2023GL104634, 1-9,  https://doi.org/10.1029/2023GL104634 .

Schoeberl, M. R., Wang, Y., Taha, G. et al. (2024): “Evolution of the climate forcing during the two years after the Hunga Tonga‐Hunga Ha’apai eruption”, J. Geophys. Res. Atmos., vol. 129, e2024JD041296, https://doi.org/10.1029/2024JD041296  .

Sellar, A., Jones, C. G., Mulcahy, J. P. et al. (2019a): “UKESM1: Description and Evaluation of the U.K. Earth System Model”,  Journal of Advances in Modeling Earth Systems, vol. 11, 4513-4558,  https://doi.org/10.1029/2019MS001739 .

Sellar, A. Walton, J., Jones, C. G. et al. (2019b): “Implementation of UK Earth System Models for CMIP6”, Journal of Advances in Modeling Earth Systems, vol. 12, e2019MS001946, https://doi.org/10.1029/2019MS001946 .

Sellitto, P., Podjlajen, A., Belhaji, R. et al. (2022): “The unexpected radiative impact of the Hunga Tonga eruption of 15th January 2022”, Comms. Earth & Env., vol. 6, 3:288, https://doi.org/10.1038/s43247-022-00618-z .

Steinbrecht, W.  (2023): “Hunga Tonga Hunga Ha’apai volcanic eruption changes the stratosphere”, in June 2023 WMO ozone and UV bulletin, https://ozone.unep.org/sites/default/files/2023-06/Ozone_and_UV_Bulletin_1_en.pdf .

Wang, Y. and Huang, Y. (2024): “Compensating atmospheric adjustments reduce volcanic forcing from Hunga stratospheric H2O vapor enhancement”, Sci. Adv., vol. 10, eadl2842, 1-6, https://doi.org/10.1126/sciadv.adl284 .

Wright, C. J., Hindley, N. P., Alexander, M. J. et al. (2022), “Surface-to-space atmospheric waves from Hunga Tonga–Hunga Ha’apai eruption”, Nature, vol. 609, 741-746, https://doi.org/10.1038/s41586-022-05012-5 .

Wu J., Cronin, S. J., Brenna, M. et al. (2025): “Missing atmospheric sulfur in the 15 January 2022 Hunga eruption and implications for completeness of paleoclimate-volcanic records“, Nature Geoscience, vol. 18, 518–524, https://doi.org/10.1038/s41561-025-01691-7 .

Zanchettin, D., Khodri, M., Timmreck, C. et al. (2016) “The MIP on the climatic response to volcanic forcing (VolMIP): experimental design & CMIP6 forcing input data”, Geosci. Mod. Dev., vol. 9, 2,701-2,719, https://doi.org/doi:10.5194/gmd-9-2701-2016

Zanchettin, D., Timmreck, C., Khodri, M. et al. (2022) “Effects of forcing differences & initial conditions on inter-model agreement in the VolMIP volc-pinatubo-full expt”, Geosci. Mod. Dev., vol. 15, 2,265-2,292, https://doi.org/10.5194/gmd-15-2265-2022  .