Coastal Impacts, Adaptation, and Vulnerabilities - Climate ...

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Physical Climate Forces 15Sea-level Rise and Effects on CoastsAlthough climate has been highly variable and sea level has changed throughout Earth’shistory, over the past approximately 6,000 years, global climate and sea level have beenrelatively stable with little variability and extremes. This benign climate has likely beena major factor in the rapid expansion of human population, which numbers 7 billionpeople currently, and the development of our modern society (Day et al., 2007). In theU.S., human population and development in coastal regions are substantial. Populationcontinues to expand and people are increasingly at risk from global warming and a varietyof natural hazards such as sea-level rise, storms, and flooding that may be exacerbatedby human-induced changes to global climate (Crossett et al., 2004; McGranahan etal., 2007; Nicholls et al., 2011).Society should be concerned about current observations of sea-level rise and projectionsof significant increases in decades ahead for two key reasons: 1) populationdensities have increased greatly and coasts have undergone intense development duringa period of relatively stable sea level over the past century. Although, in theory,people could relocate landward to accommodate rising seas, human infrastructure, privateland ownership, and current policy tend to prevent such adaptation measures. 2)Coastal landforms such as barrier islands, wetlands, and deltas are already dynamic andtherefore highly vulnerable to sea-level rise. Many coastal urban areas including Boston,New York, Washington D.C., Norfolk, Charleston, Miami, New Orleans, San Francisco,and Honolulu are also at high risk, yet few coastal states and communities have plansfor adaptation to warming temperatures, changes in storminess, and rising sea levels.Coastal landforms are not simply inundated as sea level rises, but rather are modifiedby a variety of dynamic processes with cumulative effects that vary by location. Severalconditions and driving forces influence coastal evolution in response to sea-level rise, asdiscussed by FitzGerald et al. (2008) and Williams and Gutierrez (2009):• Geologic framework and character of coastal landforms;• Impacts of major storm events;• Coastal oceanographic processes acting on the coast;• Sediment supply to the coast by erosion and rivers and transport along thecoast; and• Human activity that alters sediment movement and increases erosion.Geologic and historical records show large cyclical fluctuations in global sea level associatedwith global climate change (Church et al., 2010, 2011; Hansen et al., 2007; IPCC,2001; IPCC, 2007). For example, during the last interglacial warm period about 125,000years ago when most of the world’s glaciers and many ice sheets on Greenland weredepleted, sea level was approximately 6 to 8 meters higher than present (Kopp et al.,2009). In contrast, during the Last Glacial Maximum about 21,000 years ago when muchof North America and northern Europe were thickly ice-covered, sea level was about 120meters lower than present (see Figure 2-2) and much of present-day continental shelf areaswere exposed coastal plains (Fairbanks, 1989; Muhs et al., 2004). During the Ice Agesand lower sea level eras, rivers flowing across the coastal plain eroded large valleys.Subsequent sea-level rise submerged these river valleys, creating Long Island Sound,
16 Coastal Impacts, Adaptation, and VulnerabilitiesFigure 2-2 Generalized curve of sea-level rise since the last ice age. Abbreviations: MWP = meltwaterpulse. MWP-1A0, c. 19,000 years ago, MWP-1A, 14,600 to 13,500 years ago, MWP-1B, 11,500-11,000 years ago, MWP-1C, ~8,200-7,600 years ago. (From http://www.giss.nasa.gov/research/briefs/gornitz_09/)the Chesapeake and Delaware Bays, and San Francisco Bay. In addition, all of the barrierislands, most expanses of wetlands, and the Mississippi River delta are landformsthat were only able to form about 6,000 years ago, when the rate of sea-level rise stabilizednear its present level and sediments were able to accumulate and create landformsat the coast (Williams & Gutierrez, 2009).Inundation, Land Loss, and Land Area Close to Present Sea LevelA readily apparent impact of rising sea level is inundation. For example, as discussed inchapter 2.2, if sea level rises 1 meter in the next century, then land under 1 meter will bebelow sea level unless the land is experiencing uplift or accretion of 1 meter or greater.The 1-meter elevation contour does not necessarily correspond to the future shorelinefrom a 1-meter rise in sea level. Shoreline processes may cause land well above 1 meterto erode (Gutierrez et al., 2009), sediment accretion may enable wetlands to remain atsea level (Cahoon et al., 2009), and coastal development can lead to shore protection to
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Vulnerability and Impacts on Human
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Chapter 5Adaptation and MitigationK
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ReferencesAbuodha, P. & Woodroffe,
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Coastal Impacts, Adaptation, and Vu
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