Sea levels are constantly changing around the globe. Long-term trends in sea-level rise are linked to global climate change. Sea level changes are primarily due to the melting and freezing of the icecaps due to global temperature changes. Sea level change is also due to the expansion and contraction of the total water mass due to global temperature changes. Figure 11.12 illustrates the dramatic rise in sea level over the past 20,000 years—estimated at about 120 meters (400 feet)! Figure 11.13 shows how much sea level has risen since detailed global record have been kept (starting around 1900).
Figure 11.13 show that in most places around the coastline of North America sea level is rising, however, in some places sea level is falling. In northeastern North America the land is rising due to glacial rebound (an isostatic adjustment caused by the melting of the great Laurentide continental glacier). In Alaska and other part of the West Coast, tectonic forces are pushing up coastal regions, some of these were rapid adjustments associated with massive earthquakes.
What is Sea Level? YouTube video explaining the geodesy of defining sea level.
Sea Level Trends (NOAA website linked to data used in Figure 11.14).