The correction for glacial isostatic adjustment (GIA) accounts for the fact that the ocean basins are getting slightly larger since the end of the last glacial cycle. GIA is not caused by current glacier melt, but by the rebound of the Earth from the several kilometer thick ice sheets that covered much of North America and Europe around 20,000 years ago. Mantle material is still moving from under the oceans into previously glaciated regions on land.

The global mean sea level (GMSL) we estimate is an average over the oceans (limited by the satellite inclination to ± 66 degrees latitude), and it cannot be used to predict relative sea level changes along the coasts. As an average, it indicates the general state of the sea level across the oceans and not any specific location. Local tide gauges measure the sea level at a single location relative to the local land surface, a measurement referred to as "relative sea level" (RSL).

The term "sea level" has many meanings depending upon the context. In satellite altimetry, the measurements are made in a geocentric reference frame (relative to the center of the Earth). Tide gauges, on the other hand, measure sea level relative to the local land surface (see the tide gauge discussion and FAQ). The satellite altimeter estimate of interest is the distance between the sea surface illuminated by the radar altimeter and the center of the Earth (geocentric sea surface height or SSH).