Online Marine & coastal projections 3 Changes to sea level rise
This chapter gives projections of sea level rise (SLR) around the UK for the 21st century. Previous national projections were included in the UKCIP02 report. We have updated the projections in a number of ways, primarily through using results from the most recent IPCC Fourth Assessment Report and newer estimates of UK vertical land movement.
One component of future SLR is from the melting of large ice sheets. However, there is a lack of current scientific understanding of some aspects of ice sheet behaviour and as such there are known limitations to including this component in sea level projections. In response, we have provided a High-plus-plus () scenario for sea level rise around the UK in addition to our main scenarios. The IPCC Fourth Assessment Report provide some illustrative possibilities of how this lack of understanding of ice sheet dynamics might affect sea level projections, and the bottom of the H++ scenario range here is taken from the maximum global mean sea level rise value given by the IPCC Fourth Assessment Report. The top of the H++ scenario range is derived from indirect observations of sea level rise in the last interglacial period, at which time the climate bore some similarities to the present day, and from estimates of maximum glacial flow rate. The upper part of the range of sea level increase is thought to be highly unlikely, but we provide the scenario as some users may find it useful to aid contingency planning (see Chapter 1, Section 1.3).
Current flood guidance is based on the maximum of the global sea level range given for the High (SRES A1FI) climate scenario in the IPCC Third Assessment Report along with vertical land movement estimates based on geological data. In the Defra guidance, rates of sea level rise relative to the land are given for three large-scale UK sub-regions and for four time intervals which span the 21st century. Under this guidance for example, the projected increases for London and Edinburgh from 1990 to 2095 would be 90.5 and 72.8 cm respectively. These can be compared to the UKCP09 95th percentile high emission scenario values given here of 83.3 and 69.5 cm. The methodologies used to generate sea level ranges for the UK in this UKCP09 report differ from the current Defra guidance. Here we base the spread of projections from the more recent IPCC Fourth Assessment Report and take local oceanographic and land movement variation into account. We also used improved methods to estimate vertical land movement using models constrained by a range of observations.
- Our analysis gives projections of UK coastal absolute sea level rise (not including land movement) for 2095 that range* from approximately 13–76 cm.
- Taking vertical land movement into account gives slightly larger sea level rise projections relative to the land in the more southern parts of the UK where land is subsiding, and somewhat lower increases in relative sea level for the north. We have, for example, derived projected relative sea level increases for 1990–2095 of approximately 21–68 cm for London and 7–54 cm for Edinburgh (5th to 95th percentile for the medium emissions scenario).
- A low probability High++ sea level range has been defined for vulnerability testing. For the UK this absolute SLR estimate is 93 cm to 1.9 m by 2100.