An international assessment report provides definitive statements on the atmospheric impacts from a huge volcanic eruption in 2022.
The assessment was unprecedented, for a specific geophysical event, and involved more than 100 scientists from around the world, including four academics from the University of Leeds.
The Hunga volcano in the tropical Pacific erupted in January 2022, sending a plume of vaporised seawater deep into the stratosphere in an explosion that equalled the size of Krakatoa’s in 1883.
Based entirely on peer-reviewed research, the report brings together monitoring information from satellite measurements, field campaigns and ground-based observatories, to document the eruption’s far-reaching effects on the ozone layer and climate.
The Hunga assessment report’s main findings include:
- The eruption increased global stratospheric water vapour by about 10 percent, much of which remains in the atmosphere in 2025.
- Very large eruptions usually cause a stratospheric warming effect, but Hunga did the opposite, cooling the stratosphere, the layer of air ~10-50km above the ground.
- While Hunga did affect stratospheric ozone in the Southern Hemisphere, its effects on the Antarctic ozone hole and surface climate were minor.
Dr Yunqian Zhu, senior research scientist at the University of Colorado, Boulder and overall lead author for the report said: “The Hunga eruption was unlike anything our satellites have observed before. The eruption has shown how water-rich volcanic eruptions can affect the stratosphere and how essential global cooperation is in monitoring and understanding such rare events.”
Dr Graham Mann from the University of Leeds co-led the coordination of the report with Dr Zhu. He said: “The reason for the report is large volcanic eruptions can have substantial impacts on climate and the ozone layer, the 1991 Pinatubo eruption for example causing a two-year global cooling effect, of a quarter to half a degree Celsius.”
Dr Mann is a lecturer in atmospheric science at the School of Earth and Environment and was researching Pinatubo’s impacts with colleague Dr Sandip Dhomse for the UK National Centre for Atmospheric Science when Hunga erupted.
Dr Mann said: “Although Hunga’s surface climate impacts were only minor, the eruption caused a strong cooling of the stratosphere, and a future eruption more similar to Pinatubo would be highly relevant for the 1.5oC Paris climate target.
“The Hunga report is an amazing community effort and brings together the exciting science on the eruption’s impacts for a definitive assessment for how this unusual water-rich eruption perturbed the stratosphere.”
Professor Martyn Chipperfield from the School of Earth and Environment at Leeds, and Professor Amanda Maycock from the Priestley Centre for Climate Futures also contributed to the report.
Professor Maycock was a lead author of the Future Climate projections chapter of the 2021 IPCC climate assessment report and was review editor for the Hunga assessment report climate impacts chapter.
Professor Maycock said: “The report shows that although water vapour is a greenhouse gas, Hunga had a net cooling effect overall and did not cause the record level of global warming observed in 2023 and 2024.
“This is a very important finding as understanding what caused the recent surge in global warming is a priority for the climate science community.”
Dr Mann added: “The key metric for volcano-climate impacts is the amount of sulphur an eruption releases into the stratosphere, this determining how much sunlight the subsequent layer of volcanic sulphate aerosol reflects back out to space.
“The Hunga volcano actually released a similar amount of sulphur to Pinatubo, but the shallow underwater setting meant 95 percent of sulphur emitted from the volcano was returned to the earth’s surface. The highly abundant water vapour from the seawater made the eruption more explosive, and meant both sulphur and water vapour were released deep into the stratosphere.”
For the water vapour surface warming effect, Dr Mann commented: “Ironically, it is because Hunga emitted the water vapour so deep into the stratosphere that surface climate impacts were only small. Had this huge amount of water vapour been emitted near the tropopause, there would have been a larger surface warming effect, adding to the 2023-24 global warmth.”
Dr Dhomse and Professor Chipperfield have contributed to United Nations Environment Programme/World Meteorological Organization ozone assessment reports for over 20 years and also contribute to the UK National Centre for Earth Observation.
Dr Dhomse commented: “Hunga’s volcanic water vapour emission also means the memory of the eruption will remain for much longer than a typical sulphur-rich eruption. The extra stratospheric water vapour will continue to influence both stratospheric chemistry and dynamics for several more years, within the slow circulation of air in the middle atmosphere.”
Professor Chipperfield added: “From running models, we are able to isolate Hunga’s impacts on the ozone layer, distinguish from year-to-year variability and from human-caused impacts. Our modelling work feeds into international assessments, which are a key part of ensuring that the Montreal Protocol is on track to secure the ozone layer’s recovery.”
Further information
Top image credit: GOES (Geostationary Operational Environmental Satellites)/ NOAA Chemical Sciences Laboratory
The “Hunga Volcanic Eruption Atmospheric Impacts” report is published 18th Dec 2025 by the World Climate Research Programme (WCRP), within WCRP activity “Atmospheric Processes and their Role in Climate” (APARC), based at Forschungzentrum Juelich (FZJ) in Germany. The Open Access full Hunga report is available for download.
The report was unveiled at the AGU25 in a dedicated session on 18 December 2025.
For more information on the Hunga assessment report please contact WCRP science communications manager Carlos Montoya on cmontoya@wmo.int
For more information on the University of Leeds role in the report and to speak to the experts involved please contact the University of Leeds press office on pressoffice@leeds.ac.uk.
The National Centre for Atmospheric Science and National Centre for Earth Observations are distributed research centres in the UK, funded by the Natural Environment Research Council, and based across multiple Universities across the UK.
Satellite monitoring instruments developed by NASA, European Space Agency and the Japanese Space Exploration Agency provided data for the report, alongside ground remote sensing networks and field campaigns at Reunion Island and Sao Paulo, Brazil.