Environmental Engineering Reference
In-Depth Information
Figure 9.3
Trend in annual rainfall in conterminous United States since 1900 (T. R. Karl, R. W.
Knight, D. R. Easterling, and R. G. Quayle, “Trends in U.S. Climate during the Twentieth
Century,”
Consequences
1 [1995]: 5.)
Sea Level Rise
Sea levels are rising almost everywhere (8.7 inches since 1875), for two
reasons: glacial melting and the expansion of water as its temperature
increases. Thermal expansion is a less obvious process than melting ice
because it cannot be seen, but scientists estimate it is responsible for half
to two-thirds of measured sea level rise. About half of the amount that
results from melting ice comes from the Antarctic and Greenland ice
caps. The other half comes from melting of the world's 150,000 to
200,000 mountain glaciers—tongues of ice that are retreating landward
at an average rate of about 30 feet per year.
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It should be noted that the
melting of ice already fl oating in the ocean, such as in the Arctic, does
not affect sea level. Only the melting of land-based ice or its calving into
the ocean can cause sea level to rise.
There are many uncertainties concerning how fast ocean levels will
rise over the next few decades and centuries. For example, how fast will
humans decrease their use of fossil fuels? The industrialized nations are
