DOT Center for Climate Change | About Transportation and Climate Change

Sea level has risen worldwide approximately 15-20 cm (6-8 inches) in the last century. Approximately 2-5 cm (1-2 inches) of the rise has resulted from the melting of mountain glaciers. Another 2-7 cm has resulted from the expansion of ocean water that resulted from warmer ocean temperatures. The pumping of ground water and melting of the polar ice sheets may have also added water to the oceans.

Along most of the U.S. coast, sea level has been rising 2.5-3.0 mm/yr (10-12 inches per century). Nevertheless, the rate varies from about 1 cm per year (three feet per century) along the Louisiana Coast, to a drop of several millimeters per year (a few inches per decade) in parts of Alaska. The rapid rate in Louisiana resulted from the settling of newly created land formed by the sediments that washed down the Mississippi River. In Galveston, the removal of groundwater led the land above the water table to sink. In areas that were covered by glaciers during the last Ice Age, by contrast, the land is rising because of the removal of the weight of the ice, which had previously compressed the land downward. As a result, the sea is dropping relative to these coasts.

line graph of U.S. Sea Level Trends 1900-1997 for Galveston, TX, New York, NY, Baltimore, MD, Key West FL, San Francisco, CA and Sitka, AK. Source: National Ocean Service