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

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Physical Climate Forces 13Figure 2-1 Schematic diagram showing the main impacts of climate warming and the effects oncoasts. Source: Burkett et al., 2009.system is driven by solar energy. About 50 percent is absorbed at the surface, 30 percentis reflected back to space and 20 percent is absorbed in the atmosphere (IPCC, 2007).An increase in greenhouse gases in the atmosphere leads to increased absorption andhigher temperatures on land and in the oceans. Humans are changing Earth’s energybalance by altering land surface properties and increasing greenhouse gas concentrations.The temperature increases observed are uneven around the globe and gains andlosses are compensated by ocean and atmospheric currents. Many of these processesinvolve positive and negative feedback mechanisms that interact in complex ways; evensmall changes in atmospheric warming can have cumulative and multiplying effectsacross entire regions and even globally. These feedbacks are important in regulatingclimate affecting all aspects of the Earth system, but many of these environmental feedbacksand physical tipping points are neither well understood nor predictable with highconfidence.The coastal zone at the nexus of the continents, oceans, and atmosphere is highlydynamic but particularly vulnerable to impacts of climate change. The primary driving
14 Coastal Impacts, Adaptation, and Vulnerabilitiesforces are: sea-level rise; changes in temperature: precipitation; major storm events includingwaves, winds, and currents; and changing ocean circulation patterns.This overview is focused on sea-level rise and its effects on the ocean coast of the U.S.,including Alaska, Hawaii, and island territories. Although the Great Lakes are not discussed,many of the same factors and conclusions about the effects of climate change arelikely to apply. An exception is sea-level rise. Although oceans are likely to experiencerising levels, the Great Lakes are predicted to experience dropping lake levels in the nearfuture due to warming and increased evaporation. A drop in lake levels below historiclevels has serious implications for the entire Great Lakes region for activities that rely onfreshwater resources and commercial navigation.Discussions of other climate change driving forces acting on coasts, such as sea-levelrise scenario projections; extreme storm events; ocean waves, currents and ocean circulation;coastal vulnerability; changes in precipitation; and temperature increase arediscussed in the subsequent Chapter 2 sections that follow.Coastal Landforms and Coastal ChangeThe diverse landforms such as barrier islands and dunes, bluffs and cliffs, mainlandbeaches, deltas, estuaries and bays, and wetlands that comprise the U.S. coast are productsof a dynamic interaction between: 1) physical processes that act on the coast, includingstorms, waves, currents, sand sources and sinks, and relative sea level; 2) humanactivity such as dredging, dams, and coastal engineering; and 3) the geological characterof the coast and nearshore. Variations of these physical processes in both location andtime, as well as the local geology along the coast, result in the majority of the U.S. coastlinesundergoing overall long-term erosion at highly varying rates (CCSP, 2009a; Williamset al., 2009). The complex interactions between these factors make the relationshipbetween sea-level rise and shoreline change difficult to know. The difficulty in linkingsea-level rise to coastal change results from the fact that shoreline change is not drivensolely by sea-level rise. Instead, coasts are in dynamic balance and respond to manydriving forces such as geological character, storm activity, and sediment supply in thecoastal system. Surveys over the past century show that all U.S. coastal states are experiencingnet long-term erosion at highly variable rates. Sea-level rise will have profoundeffects by increasing flooding frequency and inundating low-lying coastal areas, butother processes such as erosion and sediment accretion will have additional importanteffects on driving coastal change.Many coastal landforms adjust to sea-level rise by growing vertically, migrating inland,or expanding laterally. If the rate of sea-level rise accelerates significantly, coastalenvironments and human populations will be affected. In some cases, the effects will belimited in scope and similar to those observed during the last century. In other cases,thresholds may be crossed, beyond which the impacts would be much greater. If the searises more rapidly than the rate with which a particular coastal system can keep pace,it could fundamentally change the state of the coast. For example, rapid sea-level risecan cause rapid landward migration or segmentation of barrier islands, disintegration ofwetlands, and drowning of coral reefs (CCSP, 2009a).
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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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