Sea level is a very sensitive index of climate change and variability. As the ocean warms in response to global warming, sea waters expands and as a result, sea levels rise. When mountain glaciers melt in response to increasing air temperature, sea levels rise because more freshwater glacial runoff discharges into the oceans.
Similarly, ice mass loss from the ice sheets causes a rise in sea level. The increase of freshwater flowing into the oceans reduces its salinity, decreasing its density and affecting ocean circulation patterns that in turn affect the sea level and its spatial variability.
The global mean level of the oceans is an indicator of climate change. It incorporates the reactions from several different components of the climate system. Precise monitoring of changes in the mean level of the oceans is vitally important for understanding not just the climate but also the socioeconomic consequences of any rise in sea level.