9. Sea Level Rise
TH Sparks and MGR Cannell
Changes in sea level at Lowestoft, Suffolk
Changes in sea level at Newlyn, Cornwall
for the period 1960-1996. Values are millimetres above a local reference height at each location (the "Revised Local Reference").
Sea level relative to the land (known as the revised local reference) is recorded at sites all around the UK as a UK Permanent Service for Mean Sea Level. Sea levels at two sites are chosen as specific indicators: Lowestoft in Suffolk and Newlyn in Cornwall.
Global mean sea level has increased by 1.0-2.0 mm per year during this century. It is predicted to rise above 1995 levels by 23 cm by the 2050s and 42 cm by the 2090s as a result of further thermal expansion and melting of land ice. The rise in sea level relative to the land will be greater than the global average in southern and eastern England because the land is sinking. By contrast, land in northern UK is rising due to adjustment following glacier-ice removal about 10,000 years ago. Coastal areas could face a significantly increased risk of flooding, inundation and erosion as a result of sea level rise, with or without more frequent and severe storm surges. At present it is not possible to predict the effect of global warming on the storm surge regime affecting UK coasts.
There is a lot at stake. About 31% of the coast of England and Wales has a built-up frontage, about 40% of UK manufacturing industry is near the coast, about 26 million people live in coastal urban conurbations, 57% of Grade 1 agricultural land in the UK is below the 5 m contour and 10% of the UK's notified nature reserves are near the coast.
Several stretches of coastline are especially vulnerable to a combination of increase in sea level and sea surge, human interventions and natural variability, especially those around the Wash, Norfolk and Suffolk coasts and, to a lesser extent, areas of Teesside and southwest Lancashire. Most studies indicate that protecting the coastline is economical, but local areas may be best left to the sea. Any sudden changes in sea surges, overtopping and breaching defences, will be especially expensive. Rising sea levels may be especially threatening to coastal aquifers (causing saline intrusion) and coastal resorts.
Change over time
Mean annual sea level fluctuates from year to year. Much of this variation is related to the position of the Gulf Stream - high sea levels occur when the Gulf Stream follows a northerly path and the Gulf Stream Position Index is large. Thus, at Lowestoft, over the period 1966-2001, the correlation between the Gulf Stream Position Index and sea level (the revised local reference level) was very significant (0.46).
A gradual increase in sea level is easily detected in the records around the southern and eastern coasts of England. At Lowestoft, mean sea level increased by 2.01 (+/- 0.42) mm per year over the period 1960-1996 and at Newlyn by 1.19 (+/- 0.31) mm per year. These are highly significant upward trends.