The Regional Impacts of Climate Change

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In estuaries, sandy beaches may be even more vulnerable than vegetated wetlands to being squeezed between rising sea level and development. A 1-cm rise in sea level generally erodes beaches about 1 m (Bruun, 1962). Thus, because estuarine beaches usually are less than 5 m wide (Nordstrum, 1992), even a 5-cm rise in sea level can eliminate these systems in areas where adjacent land is protected with structures. Moreover, the environmental regulations that protect wetlands generally have not been applied to protect estuarine beaches (Titus, 1997), which are important for recreation, navigation, and habitat for several endangered species (Nordstrum, 1992).

A 50-cm rise in sea level could inundate 8,500-19,000 km2 of dry land, even if currently developed areas are protected.

The dry land within 1 m above high tide includes forests, farms, low parts of some port cities, communities that sank after they were built and that now are protected with levees, parts of deltas, and the bay sides of barrier islands. The low forests and farms generally are in the Mid-Atlantic and Southeast. Major port cities with low areas include Boston, New York, Charleston, Miami, and New Orleans. New Orleans' average elevation is about 2 m below sea level; parts of Texas City, San Jose, and Long Beach, California, are about 1 m below sea level. In the United States, 8,500-19,000 km2 (3,300-7,300 mi2) of dry land are within 50 cm of high tide-5,700-16,000 km2 (2,200-6,100 mi2) of which currently are undeveloped (Table 8-7) (Titus et al., 1991). Approximately 100 km2 of land in the Fraser delta (British Columbia) also is within 1 m of sea level.

Table 8-7: Loss of dry land from sea-level rise (95% confidence interval, mi2).

  Rise in Sea Level (cm)
  Baseline 50 100 200

If no shores are protected NR 3,300-7,300 5,100-10,300 9,200-15,400
If developed areas are protected 1,500-4,700 2,200-6,100 4,100-9,200 6,400-13,500

NR = not reported.

Source: Titus et al., 1991.


Many islands are at risk. The low bay sides of developed barrier islands could be inundated while their relatively high ocean sides erode. Undeveloped barrier islands will tend to migrate landward through the overwash process.

The most economically important vulnerable areas are recreational resorts on the coastal barriers-generally long and narrow islands or spits (peninsulas) with the ocean on one side and a bay on the other-of the Atlantic and Gulf coasts. Typically, the oceanfront block is 2-5 m above high tide; the bay sides often are <0.5 m above high water.

Erosion threatens the high ocean sides of these densely developed islands; this oceanfront erosion generally is viewed as a more immediate problem than inundation of the islands' low bay sides. Shores currently are eroding at a rate of 0.25-0.5 m/yr in many areas. Studies using the "Bruun (1962) rule" have estimated that a 1-cm rise in sea level will cause beaches to erode 0.5-1 m from New England to Maryland, 2 m along the Carolinas, 1-10 m along the Florida coast, and 2-4 m along the California coast (Bruun, 1962; Kana et al., 1984; Everts, 1985; Kyper and Sorensen, 1985; Wilcoxen, 1986). Because many U.S. recreational beaches are less than 30 m wide at high tide, even a 30-cm rise would threaten homes in these areas.

Canada's longest barrier coast is in New Brunswick along the Gulf of St. Lawrence; the narrow barrier islands and spits generally are undeveloped. Rising sea level tends to cause narrow islands to migrate landward through the overwash process (Leatherman, 1979). Although the barriers themselves are undeveloped, there are important recreational areas along the mainland coast behind the barriers, as well as environmentally sensitive freshwater bogs and woodlands.

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