Global Mean Sea Level Rise

The Global Mean Sea Level (GMSL) has been continuously monitored using satellite radar altimetry since October 1992 on the same reference orbit through the Topex/Poseidon, Jason-1, Jason-2, Jason-3, and Sentinel-6 Michael Freilich (S6-MF) missions. Accurate characterization of GMSL's long-term stability is essential for separating physical signals from measurement artifacts and providing well-characterized uncertainties. The reference altimetry missions maintain an unchanged reference orbit since 1993, enabling precise inter-mission calibration. Tandem flight phases between successive missions, with temporal separations of only seconds, ensure continuity and stability of the sea level record. Critical to this process are continuous monitoring of instrumental performance, rigorous data quality control, homogenization of processing algorithms, and standardization of geophysical corrections. Satellite altimetry's high-accuracy sea-level monitoring allows the detection of global mean sea-level rise and its attribution to greenhouse gas emissions, thereby supporting robust climate change assessments.

Significant regional variability in mean sea level occur, with some regions rising three to four times faster than the global average. This spatial heterogeneity primarily results from heat redistribution patterns influenced by major climate oscillations, particularly the El Niño/Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and North Atlantic Oscillation (NAO). Regional mean sea level trends also reflect variations at different spatial scales, from large-scale ocean basin structures to finer mesoscale features within major ocean currents such as the Gulf Stream, the Kuroshio, and the Antarctic Circumpolar Current (around Antarctica in the Southern Hemisphere). Satellite altimetry also provides accurate measurements of regional sea level changes, and further description is the subject of a separate metadata sheet.

The AVISO (GMSL) is computed using Non-Time-Critical (NTC) Level-2 plus (L2P) along-track measurements from the reference missions only. The use of upstream calibrated and validated L2P data allows to derive a GMSL with a short latency of 3 months from the present time.

The GMSL can also be computed from the Level-4 (L4) delayed-time (DT) multi-mission gridded DUACS sea level products distributed by the Copernicus Marine Service (https://doi.org/10.48670/moi-00237).

The AVISO reference GMSL and the one derived from the Copernicus Marine Service are considered to be identical (for the same version and period) since the same altimeter standards are used to compute the sea level anomalies.