|Sea level CCI Essential Climate Variable v1.1 1993-2014 Credits LEGOS, CLS, CNES, ESA|
Sea level is a very sensitive index of climate change and variability. As the ocean warms in response to global warming, sea waters expand and, as a result, sea level rises. When mountain glaciers melt in response to increasing air temperature, sea level rises because more freshwater glacial runoff discharges into the oceans. Similarly, ice mass loss from the ice sheets causes sea-level rise. The increase of freshwater flowing into the oceans reduces its salinity, decreasing its density and affecting ocean circulation patterns that in turn affect sea level and its spatial variability.
- Why is altimetry important?
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, then Jason-1–Jason-2), 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.