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Stockholm Environment Institute, Sweden and Pacific Institute for Studies in Development, Environment, and Security


Atmospheric concentrations of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), tropospheric ozone (O3), chlorofluorocarbons (CFCs), and other trace gases are growing due to human activities. These trace gases are transparent to incoming solar radiation and trap outgoing infrared (heat) radiation, acting like a blanket to warm the Earth. Without any of these gases in the atmosphere, the surface of the Earth would be about 35 C (70 F) colder than at present, and life, if any could exist, would be quite different. This natural greenhouse effect is being intensified by human activities that accelerate the emission of these trace gases, such as the combustion of fossil fuels and deforestation. One of the direct consequences of climatic changes will be a rise in sea level due to the melting of land ice and the expansion of the upper layers of the ocean as they warm. This study presents a method for assessing the costs to society of protecting against an increase in sea level, and applies this method to the San Francisco Bay area -- a region of great ecological diversity, economic importance, and vulnerability. Hydrodynamic effects around the margin of San Francisco Bay are evaluated, structural options for protecting property are identified and chosen for threatened areas, and estimates of costs of protection are determined. For the purposes of this study, a one-meter sea-level rise was assumed, and all development below the future 100-year high tide elevation in San Francisco Bay was considered to be at risk. The types of shoreline protection proposed include constructing new levees and seawalls, raising existing levees and bulkheads, raising buildings, freeways and railroads where necessary, and replenishing beaches. The costs described here are not the total costs of protection -- for example, no estimates are available for evaluating costs of protecting natural ecosystems. Other 3 costs left out are described in detail in the text.


This research was supported by a grant from the Stockholm Environment Institute, Stockholm, Sweden.



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