Future sea levels

In an address to the UN Security Council, Secretary-General António Guterres described the phenomenon of sea level rise as a “threat multiplier” which jeopardizes access to water, food and healthcare. He also referred to the potential damage to agriculture, fisheries and tourism, and to infrastructure, such as transportation systems, hospitals and schools, and to the possibility of the “mass exodus of entire populations”. He warned that “under any temperature rise scenario, countries from Bangladesh to China, India and the Netherlands will all be at risk” (UN News, 2023). This post will focus on the risk to a single UK region, but some of the resources cited will be of much more general interest.

Climate Central describes itself as “an independent group of scientists and communicators who research and report the facts about our changing climate and how it affects people’s lives.” Its work is organised into several programs, one of which is Sea Level Rise, which aims to provide accurate information locally and globally, using maps and tools, datasets, and visual presentation (Climate Central, 2024). Sea level rise is related to temperature, and the Coastal Risk tool allows users to select a regional map, and a set of conditions including the year, the level of action taken to cut pollution, the temperature rise between 1.5 and 5°C, one of a range of data sources, and a measure of good or bad luck. The maps then can display the area affected by sea level rise, alone or with added flood risk.

It may be useful to use the Coastal Risk tool in conjunction with a map giving present land level, such as Topography UK, 2024. The largest area of the UK that is now close to or below sea level is to the north of Cambridge, but the focus of attention here will be on a smaller area southwest of Bristol, between Glastonbury and the Bristol Channel. Much of the land here is only a few metres above mean sea level, but the Bristol Channel has an extremely high tidal range, exceeding 10m, so that on high tides and in storm conditions large areas of land are below sea level. This situation is of concern not just to local inhabitants, but also to the wider region, since the main railway line and the M5 motorway between Bristol and Exeter pass through the region.

The Climate Data Portal of the Met Office provides sea-level projections for the UK coasts to 2100 (Met Office, 2024a). These give “the local sea-level change experienced at a particular location compared to the 1981-2000 average” and are based on data from UKPC18 (Met Office, 2024b). They carry the warning that “We cannot rule out substantial additional sea-level rise associated with ice sheet instability processes that are not represented in the UKCP18 projection”. For the relevant section of the Bristol Channel, projected sea level rises are approximately 10 cm by 2030, 17 cm by 2050, and 29 cm by 2100.

While these figures may not seem alarming, the Climate Central maps show the sensitivity of the area to flooding in response to such changes. Selecting the year 2030, sea level rise only, moderate pollution cuts, medium luck, exclusion of areas protected by higher land, and IPCC2021 as data source, the maps show two areas below the tideline to the west of Glastonbury, the larger on the order of 100 km², the smaller 10 km². Neither reaches the M5 motorway or the mainline railway which both run close to the endangered area. If, however, annual flood risk is added to the settings used above on the Coastal Risk Screening Tool, a stretch of about 40 km of both motorway and railway falls within the region of flood risk in 2030. This distance increases somewhat with rising sea level over the following decades, but presumably the frequency of travel disruption would increase significantly, as would flooding in the surrounding area.

The vulnerability of this section of railway is recognised by Network Rail, which owns, repairs and develops the “railway infrastructure in England, Scotland and Wales.” In its Weather Resilience and Climate Change Adaptation Plan, it notes that the “key Bristol to Exeter railway route on the low-lying Somerset levels has historically been subject to flooding during wet winters and is a key route for adaptation to climate change” (Network Rail, 2024). The point is made here that the threat from rising sea levels is augmented by the increase in rainfall anticipated due to climate change, and the Plan has a section on “Changing precipitation patterns & flooding”. Context for the railway route is provided by the Bristol to Exeter rail corridor strategic study (Network Rail, 2022) which stresses the economic importance of the route but has little to say about climate change.

In 2023 a local news platform expressed the fear that towns in the area “could be underwater by 2090 as sea levels rise” and noted that a “huge stretch of the M5 is among the places at risk” (Somerset Live, 2023). The news article lists some of the towns in danger and uses maps from Climate Central to show which towns are expected to be under water by 2120, 2140, and 2170, when about one third of Somerset is likely to be submerged. The sources cited above have concentrated on areas, dates and maps; the reader is left to contemplate the human cost.