The latest global products including uncertainties are provided via the CCI Open Data Portal

How is Sea Level measured

Past variations can be reconstructed from several indicators, but the very first measurements of sea level were made by monitoring tides in the 18th century. Although we now have a relatively dense network of tide gauges, only 20 stations (mostly along the coasts of Europe and North America) collected data throughout the 20th century. On the basis of their measurements, sea level is estimated to have risen by 10 to 20 centimetres since 1900.

Today, satellite altimetry, autonomous floats (Argo floats since 2005) and gravimetric data (GRACE satellite) enable the measurement of mean sea level variations, or some of their components. Ocean models are also used to understand and quantify those phenomena.

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, Jason-2-Jason-3, and then Jason-3-Sentinel-6), help to link up these different missions by precisely determining any bias between them. 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 and studies of the necessary corrections of altimetry data regularly add to our understanding and knowledge.

Why Sea Level varies

There are several possible components which may take their part in the mean rise in sea level: an increase in the temperature of the water, which dilates as it warms, the thawing of mountain glaciers and polar ice caps in Greenland and Antarctica, as well as melting permafrost. Changes to the amount of rainfall and evaporation also play a part, as well as runoff and inland water reserves, mainly owing to human activity such as dam construction and irrigation.

Validation reports are produced from the analysis of the Round Robin Data Package (RRDP):

The validation reports are the main input for the selection process in order to select the best algorithms in order to produce the final Sea-Level ECV products.


Different altimeter sea level products have been produced and distributed within the Sea Level Climate Change Initiative (SL_CCI) project. Access to the ECV Products and further details can be obtained by sending an email with your interest direct to the team:

Unless you make a statement in your email that you do not agree, your email address will be kept so that you can be further informed of potential evolutions regarding the dataset. It will not be used for any other purpose.