This indicator comprises several metrics to describe past and future sea level rise globally and along European coastlines:
- observed change in global mean sea level, based on reconstructions from tide gauge measurements (since 1900) and on satellite altimeter data (since 1993);
- projected change in global sea level for three different forcing scenarios;
- spatial trends in relative sea level along the European coastline, based on tide gauge stations with long time series (since 1970); and
- projected change in relative sea level across European seas.
Methodology for indicator calculation
Sea level changes can be measured using tide gauges and remotely from space using satellite altimeters. Many tide gauge measurements have long multi-decadal time series, with some exceeding 100 years. However, the data can be distorted by various regional and local effects, such as vertical land motion processes. Furthermore, there are significant gaps in the spatial coverage of tide gauges with long time series, including in Europe.
Satellite altimeters enable absolute sea level to be measured from space and provide much better spatial coverage (except at high latitudes); however, their record is limited to about 25 years. The global and European sea level trends are calculated from a combination of nine partly overlapping satellite missions. The data are corrected for seasonal variations, the inverse barometer effects and post-glacial rebound.
Sea level projections are based on process-based models, which are rooted in state-of-the-art climate model simulations. Projections for relative mean sea level in Europe consider the gravitational and solid Earth response and land movement due to glacial isostatic adjustment, but not land subsidence as a result of human activities.
Model-based projections for changes in regional sea level rise included only grid cells that are covered at least half by sea. Data for other grid cells partly covered by land and by sea were extrapolated using the nearest-neighbour method.
Justification for indicator selection
No rationale for indicator selection have been specified.
Sea level is an important indicator of climate change because it can have significant impacts on settlements, infrastructure, people and natural systems. The potential impacts include flooding, coastal erosion and the submergence of flat regions along continental coastlines and on islands. Rising sea levels can also cause saltwater intrusion into low-lying aquifers, thus threatening water supplies and endangering coastal ecosystems and wetlands.
Changes in global mean sea level result from a combination of several physical processes. Thermal expansion of the oceans occurs as a result of warming ocean water. Additional water is added to the ocean from a net melting of glaciers and small ice caps, and from the disintegration of the large Greenland and Antarctic ice sheets.
The locally experienced changes in sea level differ from global average changes for various reasons, including changes in large-scale ocean circulation, changes in the gravity field, and vertical land movement due to the ongoing effects of post-glacial rebound, local groundwater extraction or other processes.
No uncertainties have been specified.