Mean Sea Level rise

The global mean level of the oceans is one of the most important indicators of climate change. It incorporates the reactions from several different components of the climate system. Precise monitoring of changes in the mean level of the oceans, particularly through the use of altimetry satellites, is vitally important, for understanding not just the climate but also the socioeconomic consequences of any rise in sea level.

With the Topex/Poseidon, Jason-1 and now Jason-2 altimetry missions, the global mean sea level (GMSL) has been calculated on a continual basis since January 1993. 'Verification' phases, during which the satellites follow each other in close succession, help to link up these different missions by precisely determining any bias between them. In addition, permanent monitoring of quality during the missions (Calval) and studies of the necessary corrections of altimetry data regularly add to our understanding and knowledge (see the Processing and corrections applied to each mission to obtain the reference mean sea level).

The reference mean sea level since January 1993 (left) is calculated after removing the annual and semi-annual signals. A 2-month filter is applied to the blue points, while a 6-month filter is used on the red curve. By applying the postglacial rebound correction (-0.3 mm/year), the  rise in mean sea level has thus been estimated as 3.26 mm/year (mean slope of the plotted data). Analysing the uncertainty of each altimetry correction made for calculating the GMSL, as well as a comparison with tide gauges gives an error in the GMSL slope of approximately 0.6 mm/year with a 90% confidence interval. (Credits CLS/Cnes/Legos)
Download the data (NetCDF).

Although the global trend indicates a rise in the mean level of the oceans, there are marked regional differences that vary between -10 and 10 mm/year. A map of these regional trends (right) can be obtained using gridded, multi-mission Ssalto/Duacs data since 1993, which enable the local slopes to be estimated with a very high resolution (1/3 of a degree on a Mercator projection). Isolated variations in MSL are thus revealed, mainly in the major ocean currents. (Credits CLS/Cnes/Legos)
Download the data (NetCDF).

In addition to the figures and data available on this page, which are references, the section entitled Altimetry images and data features a number of alternative options: mean sea level calculated per mission, per ocean basin, or by modifying certain corrections (wet tropospheric, inverse barometer, etc.).

Comparisons between these altimetry data and those obtained using independent techniques, such as the drifting buoys of the Argo network, the GRACE gravimetry satellite, or the network of tide gauges, can not only corroborate these results but also help us establish which of the possible sources of variation in mean sea level might explain the rise observed.