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

Physical Climate Forces 19These low elevation dry land areas include the bay sides of many barrier islands,dredge-and-fill areas originally reclaimed by filling wetlands, and low-lying portions ofmany coastal cities including Boston, Philadelphia, Washington D.C., Charleston, andNew Orleans. The gradual inundation from recent sea-level rise is evident in many areasof the mid-Atlantic and Louisiana, where high tides regularly flood roads and landthat were previously dry (Craghan et al., 2010) as well as stands of ghost forests wheretrees were killed recently by brackish water (Cahoon et al., 2009; Williams et al., 2009).In some cases, the local sea-level rise has been enhanced by the local or regional landsubsidence.Historic to Present-day Sea-level RiseAnalyses of historic relative sea level records from tide gauges around the U.S. and theworld (Figures 2-3, 2-4) show that global sea level rose, on average, 19 centimeters duringthe 20th century at highly variable regional rates influenced by many factors, includingvariations in ocean density, ocean currents, and circulation patterns (Jevrejeva et al.,2008; Woodworth et al., 2008; Zervas, 2009). Rates of global sea-level rise are derivedfrom relative rates obtained from gauge data and exclude regional and local affects suchas land subsidence and uplift. A number of studies and assessments conducted in recentyears suggest that the rate of sea-level rise is likely to increase significantly during the21st century and beyond (Anderson et al., 2010; IPCC, 2007; Jevrejeva et al., 2011; Mitchumet al., 2010; Pfeffer et al., 2008; Rahmstorf, 2007, 2010). although uncertainty existsin quantitatively predicting the exact magnitude and rate of future change in sea level,compelling scientific observations from tide gauge records and, more recently, satellitealtimetry (Figures 2-5, 2-6) show that sea-level rise has been increasing since about themid-19th century from an average of 1.7 millimeters/year during the 20th century to acurrent rate of greater than 3 millimeters/year, which represent a significant increasein the past two decades over 20th century rates (Gehrels, 2010; Hamlington et al., 2011;Holgate & Woodworth, 2004; Merrifield et al., 2009; Yin et al., 2011). The main causes aremelting of alpine glaciers, Greenland and Antarctic outlet glaciers, and thermal expansionof the oceans (IPCC, 2007). A more complete discussion of future projections andscenarios of sea-level rise by the year 2100 (Figure 2-7) can be found in Section 2.2 of thischapter.Other Coastal Climate Change TrendsChange in both short- and longer-term interannual to decadal atmospheric phenomenahave profound effects on the coastal zone. Average global land and sea surface temperaturesare continually increasing, with 2010 as the hottest on record (Blunden et al., 2011).Increased atmospheric temperature and atmospheric changes such as El Niño and LaNiña induce direct affects such as sea-level rise and also cause changes in frequency,intensity, and duration of drought, precipitation, and storm events. The 2009/2010 ElNiño transitioned to the 2010/2011 La Niña period with a Pacific Ocean temperature1 degree Celsius decrease. This change induced other changes in atmospheric conditionsfavorable for Atlantic tropical storm cyclogenesis, such as weak wind shear. However,2010 was atypical with no named storms in the Gulf of Mexico and no land-fallingU.S. storms. The lack of land-falling U.S. storms was attributed to several factors and