Abstract
The UK high-plus-plus (H++) scenario for high-end sea level rise is used in sensitivity testing for significant infrastructure (e.g., nuclear facilities) and forms part of the Environment Agency planning guidance in England. However, the existing H++ scenario, developed as part of the UK Climate Projections in 2009 (UKCP09), does not reflect the latest science knowledge on ice sheet instability processes and has limitations, as revealed in consultations with users of this information. Here, we outline a new, co-produced H++ framework to inform decision-making that involves: (a) screening decisions against an updated H++ storyline that reflects major scientific advances since UKCP09; (b) evaluating adaptation options and damage costs against a wider library of alternative, plausible storylines; and, (c) a decision-exploring initiative to facilitate long-term strategic thinking. Our H++ screening storyline is based on the Intergovernmental Panel on Climate Change Sixth Assessment Report low-likelihood high-impact sea level rise assessment. In response to user needs, all storylines within the H++ framework provide time-continuous, geographically-specific sea level rise projections for the UK to 2300 and information on sea level rise rates. For all UK capital city locations, our screening storyline projects high-end sea level rise greater than: 1 m by 2100; 4 m by 2150; 9 m by 2200; and, 15 m by 2300. At all locations, maximum rates reach over 100 mm/yr. Our H++ framework can be adapted for different climate impact drivers, sectors or regions, and respond to emerging evidence and user feedback, supporting robust adaptation planning and decision-making under deep uncertainty.
| Original language | English |
|---|---|
| Article number | e2025EF006086 |
| Journal | Earth's Future |
| Volume | 13 |
| Issue number | 11 |
| Early online date | 14 Nov 2025 |
| DOIs | |
| Publication status | Published - 30 Nov 2025 |
Data Availability Statement
The H++ global and local relative mean sea level rise screening storylines presented within this paper are provided as timeseries in the Supporting Information and via the Zenodo repository (Weeks & Palmer, 2025). Global and local relative mean sea level storylines associated with the library are available as Supporting Information to Palmer et al. (2024) and have been made available via the Zenodo repository, converted to the UKCP18 baseline (Weeks & Palmer, 2025). The IPCC AR6 projections are publicly available via the Nasa-IPCC Sea Level Projection Tool and the Zenodo repository (Fox-Kemper et al., 2021; Garner et al., 2021; Kopp, Garner, et al., 2023). UKCP18 sea level data around the UK coastline is publicly available on the UK Centre for Environmental Data Analysis (CEDA) archive (Met Office Hadley Centre, 2018) and the associated localization code is publicly available via the Met Office Projecting Future Sea Level (ProFSea) tool (R. Perks & Weeks, 2023). We thank all projection authors, teams and funding agencies for making these projections and tools publicly available.Acknowledgements
We are grateful to several colleagues from the UK Met Office who participated in discussions that helped inform the development of this work, including: Ben Harrison, Emma Dyer, Laila Gohar. We would also like to thank LTIS decision-gaming workshop attendees for their contributions to discussions. We would like to thank all reviewers for providing useful feedback to improve our manuscript. The views expressed in this paper are those of the authors and do not represent the position of the Environment Agency. Co-authors names are listed alphabetically. J. Weeks, L. Allison, J. Lowe, H. Roberts and M. Palmer were supported by the Met Office Hadley Centre Climate Programme, funded by the Department of Science, Innovation and Technology (UK).Keywords
- climate change
- climate projections
- ice sheet instability
- sea-level rise
- storyline
- United Kingdom
ASJC Scopus subject areas
- General Environmental Science
- Earth and Planetary Sciences (miscellaneous)
