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

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Executive Summaryxxvffffffffffffffof oceans acidification and rates of glacier and ice sheet melt. High Confidence.Most coastal landforms, such as barrier islands, deltas, bays, estuaries, wetlands,coral reefs, are highly dynamic and sensitive to even small changes in physicalforces and feedbacks such as warming, storms, ocean circulation, waves andcurrents, flooding, sediment budgets, and sea-level rise. High Confidence.The effects of sea-level rise on coasts vary considerably from region-to-regionand over a range of spatial and temporal scales. Land subsidence in certain locationscauses relative sea-level rise to exceed global mean sea-level rise. Landuplift such as that found in Alaska and the Northwestern Pacific coast can reduceeffects of global mean rise. The effects will be greatest and most immediate onlow-relief, low-elevation parts of the U.S. coast along the Gulf of Mexico, mid-Atlantic states, northern Alaska, Hawaii, and island territories and especiallyon coasts containing deltas, coastal plains, tidal wetlands, bays, estuaries, andcoral reefs. Beaches and wetlands on steep cliff coasts and shores backed withseawalls may be unable to move landward or maintain their landform with sealevelrise. Many areas of the coast are especially vulnerable because of the oftendetrimental effects of development on natural processes. High Confidence.The gradual inundation from recent sea-level rise is evident in many regionssuch as the mid-Atlantic and Louisiana where high tides regularly flood roadsand areas that were previously dry, and in stands of “ghost forests,” in whichtrees are killed by intrusion of brackish water. High ConfidenceSea level change and storms are dominant driving forces of coastal change asobserved in the geologic record of coastal landforms. Increasingly, sea-level risewill become a hazard for coastal regions because of continued global mean sealevelrise, including possibly accelerated rates of rise that increase risk to coastalregions. As the global climate continues to warm and ice sheets melt, coasts willbecome more dynamic and coastal cities and low-lying areas will be increasinglyexposed to erosion, inundation, and flooding. High Confidence.No coordinated, interagency process exists in the U.S. for identifying agreedupon global mean sea-level rise projections for the purpose of coastal planning,policy, or management, even though this is a critical first step in assessing coastalimpacts and vulnerabilities. High Confidence.Global sea level rose at a rate of 1.7 millimeters/year during the 20th century.The rate has increased to over 3 millimeters/year in the past 20 years and scientificstudies suggest high confidence (>9 in 10 chance) that global mean sea levelwill rise 0.2 to 2 meters by the end of this century. Some regions such as Louisianaand the Chesapeake Bay will experience greater relative rise due to factorssuch as land subsidence, gravitational redistribution of ice-sheet meltwater,ocean circulation changes, and regional ocean thermostatic effects. Other regionsundergoing land uplift, such as Alaska, will experience lesser sea-level rise. HighConfidence.Variability in the location and time-of-year of storm genesis can influence landfallingstorm characteristics, and even small changes can lead to large changes inlandfalling location and impact. Although scientists have only low confidence in
xxviCoastal Impacts, Adaptation, and Vulnerabilitiesffffffffthe sign of projected changes to the coast of storm-related hazards that dependon a combination of factors such as frequency, track, intensity, and storm size,any sea-level rise is virtually certain to exacerbate storm-related hazards. HighConfidence.Although sea-level rise and climate change have occurred in the past, theincreasing human presence in the coastal zone will make the impacts differentfor the future. Land use and other human activities often inhibit the naturalresponse of physical processes and adaptation by plants and animals. In someareas, erosion and wetland loss are common because sediment budgets havebeen reduced, while, in other regions, excess sediment is in-filling harbors, channels,and bays. High Confidence.Observations continue to indicate an ongoing, warming-induced intensificationof the hydrologic cycle that will likely result in heavier precipitation events and,combined with sea-level rise and storm surge, an increased flooding severity insome coastal areas, particularly the northeast U.S. Moderate Confidence.Temperature is primarily driving environmental change in the Alaskan coastalzone. Sea ice and permafrost make northern regions particularly susceptible totemperature change. For example, an increase of two degrees Celsius could basicallytransform much of Alaska from frozen to unfrozen, with extensive implications.Portions of the north and west coast of Alaska are seeing dramatic increasesin the rate of coastal erosion and flooding due to sea ice loss and permafrostmelting. As a consequence, several coastal communities are planning to relocateto safer locations. Relocation is a difficult decision that is likely to become morecommon in the future for many coastal regions. High Confidence.Methane is a primary greenhouse gas. Large reserves of methane are bound-upin Alaska’s frozen permafrost. These are susceptible to disturbance and methanerelease if the Arctic continues to warm. The additional methane released mayresult in even greater greenhouse warming of the atmosphere. High Confidence.Vulnerability and Impacts on Natural ResourcesClimate and non-climate stressors originating from terrestrial and marine sources interactat the coast to influence coastal habitats (Nicholls et al., 2007; Rosenzweig et al.,2007). Increased temperatures and altered precipitation patterns interact with changingland use and land cover practices to affect soil moisture, ground water levels, hydrology,sediment supply, and salinity in watersheds. Sea-level rise, changing ocean currents,increased wave heights, and intensification of coastal storms interact with the shorelineto exacerbate coastal erosion, flooding, and saltwater intrusion. As the physical environmentchanges, the range of a particular ecosystem will expand, contract, or migrate inresponse. Changes in range as well as structure and function are evident in many typesof ecosystems.The interactions of the many stressors result in complex changes to natural coastalsystems that may not be predicted by the response from any single stressor. Positiveand negative impacts occur when the impact of one stressor is either strengthened or
Page 1: National Climate Assessment Regiona
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Page 8: Coastal Impacts, Adaptation,and Vul
Page 11 and 12: Chapter 3Lead Author: Carlton H. He
Page 16 and 17: ContentsKey TermsAcronymsCommunicat
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Page 20 and 21: Key TermsxixExposure 3 - The nature
Page 22 and 23: AcronymsxxiNAO - North Atlantic Osc
Page 28 and 29: Executive Summaryxxviiweakened by v
Page 30 and 31: Executive SummaryxxixAdaptation and
Page 34: Introduction and Context 3irrigatio
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Page 42 and 43: Physical Climate Forces 11fffffffff
Page 44 and 45: Physical Climate Forces 13Figure 2-
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Physical Climate Forces 43depth qua
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Physical Climate Forces 45precipita
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Physical Climate Forces 47Sea and w
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Physical Climate Forces 49by sea ic
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Physical Climate Forces 51niche ero
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Vulnerability and Impacts on Natura
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Vulnerability and Impacts on Human
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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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