Estimates of Future Sea Level Rise

Accurate monitoring of atmospheric carbon dioxide began 25 years ago. Since then, sufficient scientific evidence has been developed for two National Academy of Sciences review panels to conclude that sometime in the next century, atmospheric concentrations of C02 will almost certainly double and raise the atmosphere's mean surface temperature by at least 1.5C (2.7 F) and possibly as much as 4.5 C (8.1 F) (Charney, 1979). Such a warming should also raise the global sea level. While adequate knowledge of the various determinants of sea level rise has been developed, until now this diverse knowledge has not been used to estimate possible sea level rise trends. This chapter presents a range of sea level rise estimates, termed scenarios, that were developed on the basis of knowledge collected from a variety of disciplines, including energy economics, geochemistry, biology, atmospheric physics, oceanography, and glaciology. The most restrictive assumptions from these disciplines were linked together to generate a "conservative" scenario, which projects a sea level rise of 56.2 cm (22 in) by 2100. The least restrictive assumptions were used to generate a "high" scenario, which projects a rise of 345 cm (11.5 ft) by 2100. Two mid-range scenarios were also developed, the mid-range low scenario which projects a rise of 144 cm (4.8 ft) and the mid-range high scenario which projects a rise of 216 cm. (7 ft). In the author's judgment, future sea level rise is most likely to fall in this range. Although the scenarios span a wide range of sea level rise, they can still be used in analyzing environmental and economic impacts and to evaluate options for preventing or mitigating the adverse effects of this phenomenon. Narrowing the range of estimates of sea level rise would, of course, make these tasks easier. But rapid progress will be made only if funding is increased for key scientific disciplines. Thus, policy makers in government and business may also wish to use the scenarios in making their own assessments of the economic value of developing more precise sea level rise estimates.