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

Physical Climate Forces 11ffffffffffffffsuch 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 Confidence.Sea 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 inthe 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 susceptibleto temperature change. For example, an increase of two degrees Celsius could