As our atmosphere and oceans continue to warm, sea levels are likely to continue to rise for many decades, if not centuries. Without doubt, climate change is the primary cause of sea-level rise. Ice lost to the ocean from the Greenland and Antarctic ice sheets and from mountain glaciers together account for about 45% of sea-level rise. Copernicus Sentinel-6 is taking on the role of radar altimetry reference mission, continuing the long-term record of measurements of sea-surface height started in 1992 by the French–US Topex Poseidon and then the Jason series of satellite missions.