Erosion at Hunstanton cliffs, Norfolk. Rising sea levels are affecting a large proportion of the coast in this region

© Environment Agency

Growing populations and urbanisation of the coastal zone means that increasing numbers of people are vulnerable to extreme rises in sea level, particularly in south-eastern parts of the UK. Sea level changes affect inter-tidal habitats and groundwater status. Rising sea levels imply more flooding and more coastal erosion by waves, for any given storm scenario.

For this assessment we used data from global and UK-wide networks of tide gauges, satellites, and climate modelling. Most findings are available in the scientific literature and have been included in the periodic assessments published by the Intergovernmental Panel on Climate Change (IPCC).

Global sea level rose by about 1.7 mm per year during the 20th century (Figure 2.4); the few long European records suggest this rate of rise was slightly faster than in the 19th century. The rate of rise around the UK coast, adjusted for land movements, was slightly less at about 1.4 mm per year during the 20th century. However the rise was not steady. For example, in the 1990s sea level rose by 3 to 4 mm per year.

Oceanic tides around the UK generally show some local short-term variations in height and timing, but no long-term trends. However, there is a long-term increase in mean tidal range at Newlyn (south-west Cornwall), notable for its long well-maintained record, open-sea location and lack of harbour works. Extreme sea levels (mean + tide + storm surge) are rising at about the same rate as mean sea level.

The most significant missing piece of this puzzle is a fuller understanding of the connection between the causes of sea level rise and the effects. To address this, scientists are attempting to set up a coherent global monitoring system for sea level (altimetry, space gravity, tide gauges) and for the factors that cause changes in sea level (mass balance of ice sheets and glaciers; temperature and salinity of the ocean; water in rivers, lakes, soils and the rocks below). This will give us greater confidence in model predictions of future change, which should enable more effective coastal planning and management.