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7 Sea Level Rise and the Coastal Environment
Pages 235-256

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From page 235...
... Foremost among these is sea level rise, which threatens people, ecosystems, and infrastructure directly and also magnifies the impacts of coastal storms. Coastal environments face a variety of other stresses, such as pollution, development pressures, and resource harvesting, that can interact with climate-related changes and potentially increase the vulnerability of coastal areas.
From page 236...
... . For example, in the late 19th century, when tide gauge readings begin to provide accurate global sea level estimates, the rate of sea level rise was about 0.02 inches (0.6 millimeters)
From page 237...
... Distinguishing the effects of natural climate variability from human-caused warming is one of the challenges of understanding the details of past sea level rise and anticipating its future course.
From page 238...
... Geological processes (subsidence and uplift) , ocean circulation changes, and other processes are important for determining local and regional rates of sea level rise, but the total volume of the world's oceans -- and hence global average sea level -- is essentially controlled by thermal expansion and addition of water from land-based sources.
From page 239...
... Approximately 50 percent of the observed sea level rise since the late 19th century has been attributed to thermal expansion of the warming oceans (Gornitz et al., 1982)
From page 240...
... Ice Sheets Land ice contained in the world's glaciers and ice sheets contributes directly to sea level rise through melt or the flow of ice into the sea (Figure 7.4)
From page 241...
... of sea level stored in the West Antarctic Ice Sheet (Bamber et al., 2009) , this potential instability is of great importance to future sea level rise.
From page 242...
... reveal that ice sheet thinning is mainly confined to the margins for both the Greenland and Antarctic ice sheets. This observation can be ascribed to ocean-driven melting, a mechanism supported by the recent discovery of a warming ocean around Greenland that appears to be contributing to year-round calving into the ocean (Hanna et al., 2009; Holland et al., 2008; Rignot et al., 2010; Straneo et al., 2010)
From page 243...
... . However, unlike the Greenland and Antarctic ice sheets, mountain glaciers are relatively small and do not carry the potential for large and sudden contributions to sea level rise.
From page 244...
... Unfortunately, we do not yet have a good understanding of the processes that control the flow rates; consequently, the potential for rapid ice sheet losses is not well understood at this time. This uncertainty prevented the IPCC from providing a quantitative estimate of how much ice sheet losses might contribute to sea level rise in the coming century.
From page 245...
... ; furthermore, the risk of ice sheet collapse, and the attendant large rates of sea level rise, will increase if GHG concentrations in the atmosphere continue to increase. The task of determining how much sea level rise to expect, when to expect it, and its regional character is a critical scientific challenge given the large numbers of people, assets, and economic activity at risk, and the substantially different planning and management challenges managers would face if they had to prepare for and adapt to a sea level rise of 2, 4, or 8 feet over the course of one century.
From page 246...
... Role of Ice Sheets in Producing Potential Climate Surprises The same factors that can contribute to accelerated sea level rise over relatively short periods of time could also potentially lead to other abrupt climate changes or "climate surprises" (see Chapter 6)
From page 247...
... Thus, while the risk of these and other possible abrupt changes in climate should be taken seriously, much work remains to develop confident projections of future ocean circulation changes resulting from the ongoing freshening of the North Atlantic. Impacts of sea level rIse and other clImate changes on coastal envIronments Coastal areas are among the most densely populated regions of the United States, and around the world.
From page 248...
... Relatively small changes in average sea level can have dramatic impacts on storm surge elevation and on the inland extent and frequency of flooding events, depending on coastal topography and the existence of protective structures such as 2 The selection of the most appropriate demographic data set for evaluating vulnerability to sea level rise (or any other impact of climate change) depends on the focus, scale, and purpose of the study (see, e.g., Crowell et al., 2010)
From page 249...
... on land loss, housing structures, property values, and building contents, as well as integrated impact analyses of combined sea level rise and extreme events; the wider impacts of sea level rise on economies dependent on coastal areas; and the cost of various response options (e.g., seawalls and other hard structures to prevent inundation or erosion loss, beach nourishment requirements as higher sea levels increase the rate of coastal erosion and sediment movement, and relocation or retreat from the shoreline; e.g., Bosello et al., 2007; Nicholls et al., 2007; Yohe et al., 1999)
From page 250...
... ) -- not considering potentially much larger increases due to rapid decay of the Greenland or West Antarctic ice sheets -- tens of millions of people worldwide would still become vulnerable to flooding due to sea level rise over the next 50 years (Nicholls, 2004; Nicholls and Tol, 2006)
From page 251...
... . RESPONDING TO SEA LEVEL RISE General scientific understanding of people's vulnerability and ability to adapt to sea level rise and other climate changes has increased substantially in recent years, though place-based, sector-specific knowledge remains extremely limited.
From page 252...
... . While there is extensive research about, and experience dealing with, coastal hazards, significant further research is required to determine the most appropriate, cost-effective, least ecologically damaging, and most socially acceptable adaptation options in the face of significantly faster rates of sea level rise than has been historically experienced.
From page 253...
... Comprehensive, simultaneous, and sustained measurements of ice mass and volume changes and ice velocities are needed, along with measurements of ice thickness and bed conditions, both to quantify the current contributions of ice sheets to sea level rise and to constrain and inform ice sheet model development for future assessments. These measurements, which include satellite, aircraft, and in situ observations, need to overlap for several decades in order to enable the unambiguous isolation of ice melt, ice dynamics, snow accumulation, and thermal expansion.
From page 254...
... Methods for identifying preferences and weighing alternative adaptive responses will be needed as environmental and social conditions change over time. Frameworks and approaches need to be developed for the evaluation of market and nonmarket values of affected assets and habitats; of the economic costs and other consequences of different response options to sea level rise on both highly developed and less developed shorelines; and of the social and environmental feasibility of different adaptation options (including technological, economic, physical, ecological, social, or legal options)
From page 255...
... There is a significant shortage of expertise to conduct place-based vulnerability and adaptation needs assessments in coastal regions of the United States (as well as in other sectors and regions, as discussed in Chapter 4) , making it extremely challenging to meet the rapidly increasing demand for such information by decision makers.


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