Drowned and Rising: A Bathtub Model of Britain and the World from the Last Glacial Maximum to an Ice-Free Earth

Sea level has changed by more than 120 metres since the last Ice Age and could change by tens of metres more if the remaining ice sheets melted. I built a simple, openly documented bathtub model to show what that range means for Britain and the world, and an interactive map that lets readers set the sea anywhere from −130 m to +70 m. The model uses AWS Terrain Tiles elevation and bathymetry at three resolutions (about 10 km worldwide, 700 m around Britain and 190 m for UK statistics), fixes today's coast with Natural Earth, and floods only cells joined to the ocean. At the Ice Age low of −125 m it exposes 19.4 million km² of sea floor outside Antarctica, and almost all of the southern North Sea becomes dry land. Using today's seabed, Britain's last land link to the continent goes under at −30 m and Ireland's link to Britain at −38 m. At +7 m, about the sea-level equivalent of the Greenland ice sheet, the model drowns 4.3% of the UK's land and reaches the centre points of 61 UK towns and neighbourhoods home to 4.4% of the people of England and Wales. At +70 m those figures rise to 33% of the land and 60% of the people, and worldwide to 10.2% of land outside Antarctica and 12,857 cities with 1.91 billion people. The model ignores defences, tides, land movement and changes to the seabed; it describes broad shapes, not local flood risk. Interactive version: https://tristan-hotham.github.io/sea-level/. Data and code: https://github.com/Tristan-Hotham/sea-level. Blog post: https://blog.tristanhotham.com/2026/10/28/sea-level/. Elevation: AWS Terrain Tiles (Mapzen; ETOPO1, GMTED2010, SRTM, EU-DEM and others). Coast: Natural Earth (public domain). Cities: GeoNames (CC BY 4.0). Contains OS data © Crown copyright and database right 2026; ONS data (Open Government Licence v3.0).