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 satellite 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 (Topex/Poseidon--Jason-1, Jason-1--Jason-2, then Jason-3--Jason-2), help to link up these different missions by precisely determining any bias between them. Saral, Envisat, ERS-1 and ERS-2 are also used, after being adjusted on these reference missions, in order to compute Mean Sea Level at high latitudes (higher than 66°N and S), and also to improve spatial resolution by combining all these missions together. 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).

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The reference global mean sea level (GMSL) based on data from the TOPEX/Poseidon, Jason-1, Jason-2 and Jason-3 missions is estimated from January 1993 to present, after removing the annual and semi-annual signals and applying a 6-month filter.
By applying the postglacial rebound correction (-0.3 mm/yr), the rise in mean sea level has thus been estimated as 3.4 mm/year (straight line on the figure).
Analysing the uncertainty of each altimetry correction used in the estimation of the GMSL, as well as a comparison with tide gauges, yields an uncertainty in the GMSL trend of approximately 0.4 mm/yr at the 90% confidence level. The uncertainty range (90% confidence level) of the GMSL data at each time step has also been estimated (Ablain et al., 2018). It is superimposed to the GMSL curve in the figure (shaded area).

The dashed line displayed over 1993-1998 is an estimation of the GMSL evolution after correction of the TOPEX-A instrumental drift (Ablain et al. 2017b). It is estimated from an empirical correction derived by comparing altimeter and tide-gauge sea level data comparisons (see more details in page “validation”). The Topex-A instrumental drift led to overestimate the GMSL slope during the first 6 years of the altimetry record. Accounting for this correction changes the shape of the GMSL curve, that is no more linear but quadratic, indicating mean sea level acceleration during the altimetry era. Currently, this empirical correction is not applied to the AVISO GMSL data set, waiting for the ongoing TOPEX reprocessing by CNES and NASA/JPL.
(Credits CLS/Cnes/Legos)

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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. These spatial patterns are not stationnary. As a result, sea level trends patterns observed by satellite altimetry are transient features.
Further information on Regional Variability and past sea level reconstructions.

Combined map of regional patterns of observed sea level (in mm/year). This map 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 (1/4 of a degree on a Cartesian projection). Isolated variations in MSL are thus revealed, mainly in the major ocean currents and ENSO events (Credits EU Copernicus Marine Service, CLS, Cnes, Legos).
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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.

26 years of animation of the mean sea level [1993 to 2019].