NOAA Oceanic & Atmospheric Research | Climate Portal | Climate Program Office | Climate Observation Division

Why We Observe the Ocean

Sea Level

• Sea level rise is both an impact and a diagnostic of the Earth’s energy imbalance caused by greenhouse warming. Sustained observations are required to elucidate the variability and trends of sea level rise and their causes.

• Sea level rises in a warming climate for two primary reasons: (1) when seawater warms it expands, and (2) when land-based glaciers, snow and ice melt they add water to the ocean. 

• By independently evaluating changes in the mass of the ocean, globally averaged sea level rise provides a sensitive measure of how much heat is sequestered in the ocean as a consequence of greenhouse warming,.



• Sea level rise differs greatly from region to region because of differences in local land rise or subsidence; geographically differing ocean currents that influence how much water is piled up against coastlines; and variations in ocean heat content, salinity, atmospheric pressures, winds and currents that occur as a consequence of natural variability (for example, El Niño).

• Rising sea levels have profound impacts on coastal communities and ecosystems via gradual inundation of low lying areas that causes flooding and erosion, intrusion of salty waters into freshwater systems, and damage due to enhanced storm surges.