The January 2022 Hunga-Tonga Hunga Ha’apai 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.
2. The unusual volcanic forcing from the January 2022 Hunga-Tonga Hunga Ha’apai 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-Tonga 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-Tonga’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.
3. PhD aligns with new Hunga-Tonga SPARC 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 Tonga impacts report, aligned to the next WMO/UNEP Scientific Assessment of Ozone Depletion (see https://www.sparc-climate.org/activities/hunga-tonga/ ).
A landmark study currently in review on the longevity of the Hunga-Tonga 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-Tonga 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 SPARC international activity, and the 2025 Hunga-Tonga impacts report.
4. 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-Tonga 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 Tonga case study in preparedness for future major phreato-Plinian eruption.
The UKESM experiments will stem from satellite measurements of the Hunga-Tonga 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-Tonga-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.
5. Fit to NERC strategy
Major volcanic eruptions are an important driver of climate variability, and the dual forcing 2022 Hunga-Tonga Hunga-Ha’apai eruption has provided a different observed case for a more diverse representation of volcano-climate impacts in earth system models.
The research here therefore aligns strongly with NERC’s priority science themes, across a more resilient enviroment (risk from potential future major phreato-Plinian eruption) and in pushing the frontiers of understanding within this new volcano-climate science area.
6. CASE status for PhD studentship
We will apply for CASE status retrospectively, after the recruitment process, and although this project does not yet have CASE approval, there is strong alignment also with Met Office strategic areas.
We have discussed with both Met Office supervisors, and Dr. Johnson and Dr. Manners have agreed to be lead and co-lead supervisor, respectively.
Dhomse, S. S., K. M. Emmerson, G.W. Mann et al. (2014), “Aerosol microphysics simulations of the 1991 Mt Pinatubo eruption with UKCA composition-climate model”, Atmos. Chem. Phys., 14, 11221–11246, https://doi.org/10.5194/acp-14-11221-2014.
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
Findell, K., R. Sutton, N. Caltabiano, A. Brookshaw, P. Heimbach, M. Kimoto, S. Osprey, D. Smith et al. (2023) “Explaining and Predicting Earth System Change: A World Climate Research Programme Call to Action”, Bulletin of the American Meteorological Society, https://doi.org/10.1175/BAMS-D-21-0280.1 .
Forster, P. M., Smith, C., et al. (2023) “Indicators of Global Climate Change 2022: annual update of large-scale indicators of the state of the climate system and human influence”, Earth Syst. Sci. Data, 15, 2295–2327, https://doi.org/10.5194/essd-15-2295-2023 .
Jenkins, S., Smith, C., et al. (2023) “Tonga eruption increases chance of temporary surface temperature anomaly above 1.5 °C”, Nature Climate Change, https://doi.org/10.1038/s41558-022-01568-2 .
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., 9, 6109–6118,
Jucker, M., Lucas, C. and Dutta, D. (2023, in review): “Long-term surface impact of Hunga Tonga-Hunga Ha’apai-like stratospheric H2O injection”, http://dx.doi.org/10.22541/essoar.169111653.36341315/v1 .
Khaykin, S. et al. (2022), “Global perturbation of stratospheric water & aerosol burden by Hunga Tonga eruption”, Comms Earth & Env., vol. 3, 316 | https://doi.org/10.1038/s43247-022-00652-x
Marshall, L. A. et al. (2019): “Exploring How Eruption Source Parameters Affect Volcanic Radiative Forcing Using Statistical Emulation”, J. Geophys. Res. Atmos., 124. https://doi.org/10.1029/2018JD028675
Millan, L. et al, (2022): “The Hunga Tonga-Hunga Ha’apai Hydration of the Stratosphere”, Geophys. Res. Lett., https://doi.org/10.1029/2022GL099381
Rowell, C. et al. (2022): “External surface water influence on explosive eruption dynamics, with implications for stratospheric sulfur delivery and volcano-climate feedback”, Frontiers Earth Sci. 10:788294. http://doi.org/10.3389/feart.2022.788294
Sellar, A. et al (2019a): “UKESM1: Description and Evaluation of the U.K. Earth System Model”, Journal of Advances in Modeling Earth Systems. https://doi.org/10.1029/2019MS001739 .
Sellar, A. et al (2019b): “Implementation of UK Earth System Models for CMIP6”, Journal of Advances in Modeling Earth Systems, https://doi.org/10.1029/2019MS001946 .
Steinbrecht, W. et al. (2023): “Hunga Tonga-Hunga Ha’apai 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
Wright, C. 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 .
Zanchettin, D. et al. (2016) “The MIP on the climatic response to volcanic forcing (VolMIP): experimental design & CMIP6 forcing input data”, GMD, https://doi.org/doi:10.5194/gmd-9-2701-2016
Zanchettin, D. et al. (2022) “Effects of forcing differences & initial conditions on inter-model agreement in the VolMIP volc-pinatubo-full expt”, GMD, https://doi.org/10.5194/gmd-15-2265-2022 .