Image Credit: NASA/JPL-Caltech 

Globally-averaged, or global mean sea level (GMSL), has been accurately observed by satellite altimeters since the early 1990s. Sentinel-6 Michael Freilich will continue these observations after its launch on 21 November 2020. Modern day sea-level rise began in the late 1800s, and has been observed by tide gauges around the world since the beginning of the 20th century. A recent study (Frederikse et al., 2020) has reconstructed sea level rise and discussed the causes since 1900 using a probabilistic framework with improved observational data. The study demonstrates that the GMSL can be explained by a combination of thermal expansion of the ocean, ice-mass loss, and changes in terrestrial water storage across this entire period, while the relative importance of each component varies over time. These elements can be observed by current and future satellite missions, including GRACE/GRACE-FO, Sentinel-6A, and SWOT and quantified by projects such as MEaSUREs.

In the figure, the blue line is the reconstructed GMSL from tide gauges, constrained by GRACE and GRACE-FO mission observations in the more recent period (2003-2018). The orange line is the GMSL from satellite altimeters estimated as part of the MEaSUREs project. The agreement between the two demonstrates the robust measurement of globally-averaged sea level rise across completely independent observing systems.