Sea level is not level: the case for a new approach to predicting UK sea-level rise

Abstract

ABSTRACTCurrent predictions for future sea-level rise along the UK coasts are based on IPCC values for global mean sea-level change combined with information on land movements, changes in tidal range and storm surges. In this article we argue that the global IPCC sea-level values should be replaced by a suite of regional values, to take into account known processes that cause regional changes in sea-surface topography. Quantification of these processes, which include gravitational adjustments of the ocean surface and nearshore ocean-density changes, requires the use of numerical ocean and geophysical models. ‘Ocean siphoning’ and ‘continental levering’ are two additional mechanisms that are not included in IPCC assessments, but can be quantified using a modelling approach. Data of vertical land movements based on geological information alone, as presently used by UKCIP (Defra) in UK sea-level rise scenarios, are potentially unreliable as they represent, in essence, values of relative land-level (or sea-level) change. These data can be improved by including geophysical model predictions and GPS measurements in assessments of vertical land motion. A combined modelling/geological approach will produce more robust regional sea-level predictions for the UK that are of real practical value to agencies responsible for coastal defence and flood protection.