Sector Reports Blank (Part Opener) Chapter 3 Sea-Level Rise and Coasts
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PART 2 SECTOR REPORTS BLANK (PART OPENER) CHAPTER 3 SEA-LEVEL RISE AND COASTS nticipated climate changes will greatly amplify risks where water temperatures have risen an average of 0.1°F A to coastal populations. By the end of the century, a (0.06°C) between 1955 and 1995, down to a depth of two to five-fold increase in rates of global sea-level rise around 10,000 feet (3000 meters); (Levitus et al., 2000). could lead to inundation of low-lying coastal regions, Most of the observed sea-level rise can be attributed to including wetlands, more frequent flooding due to storm thermal expansion of the upper ocean layers and melting surges, and worsening beach erosion (IPCC, 1996a,b). of mountain glaciers, with nearly zero contributions from Saltwater could penetrate further up rivers and estuaries polar ice sheets at present (Warrick et al., 1996). Human and infiltrate coastal aquifers, thereby contaminating modification of the hydrologic cycle could also affect sea- urban water supplies. level rise. Sequestration of water on land in reservoirs and In the metropolitan New York, Connecticut, and New through irrigation losses could exceed amounts transferred Jersey region, as elsewhere, the coastal zone is squeezed seaward by groundwater mining and increased runoff due between the hazards of flooding, beach erosion, and sea- to urbanization and deforestation. The net effect of these level rise on the one hand, and development pressures on processes could slow sea-level rise by 0.04±0.02 inches/ the other hand. In the region, ongoing sea-level rise and year (0.9±0.5 millimeters/year) (Gornitz et al., 1997; land subsidence have historically contributed to beach Gornitz, 2000). erosion, narrowing of barrier islands, and storm-related Closely linked atmospheric-oceanic processes such as damages. These processes will continue and possibly wors- the El Niño-Southern Oscillation or the North Atlantic en, if projected climate changes materialize. Oscillation generate considerable interannual variability This report focuses on potential impacts of sea-level in ocean heights, superimposed on longer-term trends rise on the Metropolitan East Coast (MEC) Region and (Nerem, 1999; Hurrell, 1995). Above-average sea levels, how natural processes interact with increasing urbaniza- coastal storms, and cliff erosion are associated with El tion and other land-use changes. We present the results of Niño events on the U.S. West Coast (Komar and Enfield, a suite of sea-level projections for several plausible scenar- 1987). While above-average sea levels occur in the south- ios of climate change in the MEC Region. Estimates are eastern United States and northwestern Europe during also made of future coastal flood heights, return intervals, the positive phase of the North Atlantic Oscillation, its increases in sand volumes and costs for beach nourish- effects on the MEC Region are less clearly defined (Maul ment under these scenarios at selected case study sites and Hanson, 1991; V. Gornitz, unpubl. data). (Figure 3-1). Implications of these findings for coastal The future of the Antarctic ice sheet introduces a major management are also discussed. uncertainty into sea-level projections. Most global cli- mate models anticipate higher rates of Antarctic snow/ice Global Sea-Level Trends accumulation than melting. This would remove water from Mean global sea level has been increasing by 0.04 to 0.1 the ocean and reduce sea level (Warrick et al., 1996). On inches/year (1–2.5 millimeters/year), for the last 150 the other hand, a large part of the West Antarctic ice years, with 0.07 inches/year (1.8 millimeters/year) con- sheet is potentially unstable because it rests on land now sidered the “best estimate” (Warrick et al., 1996; Gornitz, 1995a). This is the most rapid rate within the last few thousand years (Varekamp and Thomas, 1998; Gornitz, Vivien Gornitz, Center for Climate Systems Research, 1995b) and is probably linked to the 20th century global Columbia University and Goddard Institute for Space warming of over 1°F (0.6°C) (IPCC, 2001). Additional Studies, with contributions from Stephen Couch, U.S. Army Corps of Engineers, New York District evidence of warming comes from the world’s oceans, 21 addition to the more recent global sea- New York Connecticut level signal (Gornitz, 1995b). Indicators of former sea level (e.g., mollusks, corals, peats, woods, etc.) going back Long Island Sound thousands of years can be used to derive New Jersey Montauk a long-term sea-level curve, which Long Island includes these geologic trends. Sub- New York traction of long-term trends from the City Westhampton Beach recent sea-level data leaves the cli- Long Beach mate-related absolute sea-level change. The Battery, NYC Rockaway Beach The absolute average sea-level rise for Raritan Bay Coney Island eastern North America is 0.05±0.03 Sea Bright inches/year (1.3±0.7 millimeters/year; Atlantic Ocean Asbury Park Sandy Hook Appendix Coast 1). FIGURE 3-1 Study site locations. At present, the rate of relative sea- level rise in the MEC region varies between 0.09 inches/ year (2.20 millimeters/year) in Port Jefferson, Long Island below sea level or forms floating ice shelves, which are and 0.15 inches/year (3.85 mm/yr) in Sandy Hook, New locally “pinned” or stabilized by submarine ridges. These Jersey (Table 3-1). In New York City, the rate is 0.11 inch- prevent rapid discharge of ice from fast-moving ice streams. es/year (2.73 millimeters/year, Table 3-1). These values lie Ocean warming could eventually thin and “unpin” these above the estimated global mean sea-level rise, because of shelves, which would accelerate the calving of icebergs the ongoing regional subsidence, but vary slightly from into the ocean. The melting of this additional ice over place to place due to various local factors. several centuries could raise sea level by some 16.4–19.7 feet (5–6 meters). This process, although considered very Coastal Stressors Independent of Climate unlikely, would have devastating consequences on low- The coastal zone in the MEC region is subject to a num- lying coastal areas worldwide, if it were to occur (Oppen- ber of natural and human-induced pressures. Beaches are heimer, 1998). continually changing as sand is shifted by waves, tides, and currents. Beaches are eroding and barrier islands nar- Regional Sea-Level Trends rowed or driven landward, in part due to ongoing sea-level Sea level has been rising along the U.S. East Coast since rise and land subsidence. the end of the last glaciation. Although most deglaciation The relative vulnerability of different coastal environ- ended over 6,000 years ago, sea level has continued to ments to sea-level rise has been quantified at regional to change due to the time lag with which the earth’s crust national scales using information on coastal geomorphol- has responded to the redistribution of mass on its surface ogy, rates of relative sea-level rise, past shoreline move- following the removal of the ice (i.e., glacial isostatic ment, topography, and other factors (Gornitz and White, changes). These sea-level changes are spatially non-uni- form over time scales of thousands of years to the present. TABLE 3-1 The MEC region lies at the southern edge of the last Relative sea-level trends—New York, Connecticut, ice sheet. The area to the south was upwarped during the New Jersey Tri-State region Wisconsinan glaciation 20,000 years ago (the “peripheral Station Relative Record Length bulge”), while land to the north was depressed beneath Sea Level Rise Year the weight of the ice. As land formerly under the ice sheet mm/yr in/yr rebounded, most of the Atlantic Coast has subsided. (The New London, CT 2.10 0.083 64 zone of subsidence due to the collapsed peripheral bulge Bridgeport, CT 2.57 0.101 32 has migrated northward over time to the Canadian Mari- New Rochelle, NY 2.05 0.081 25 time Provinces. The area north of the St. Lawrence valley Montauk, NY 2.27 0.089 49 is currently rebounding). Geophysical models have been Port Jefferson, NY 2.20 0.087 32 used to filter these crustal motions from tide-gauge data in Willets Point, NY 2.30 0.091 64 the eastern United States (Peltier, 1999; Davis and New York City, NY 2.73 0.107 140 Mitrovica, 1996). Sandy Hook, NJ 3.85 0.152 64 Tide gauges measure relative sea-level change, which Atlantic City, NJ 3.97 0.156 85 includes glacial isostatic and other geologic signals, in Stations lying within the Metro East Coast region are in bold. 22 1992; Gornitz et al., 1994). These physical variables are Beaches and other open coastal areas represent a prime then combined into a Coastal Vulnerability Index (CVI), recreational resource, that offers the urban population of which ranks the relative vulnerability of the coast into the MEC region relief from summer heat and leisure activi- one of four risk categories from High to Low. This meth- ties including swimming, fishing, and boating. As popula- odology has recently been updated and refined by the U.S. tion continues to grow and additional land is converted to Geological Survey (Thieler and Hammar-Klose, 1999). higher density urban uses, less area remains to expand Most of the south shore of Long Island and the New existing public parks and beaches. Furthermore, many sea- Jersey coast, which consist predominantly of barrier islands, side communities, particularly on Long Island, limit beach lie in the High to Very High risk categories. On the other access to non-residents, thus augmenting utilization pres- hand, the north shore of Long Island and the Connecticut sure on existing public facilities.