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.
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