Changes in climate are expected to affect the ocean environment in a variety of ways. The potential effects of a temperature increase include thermal expansion and the melting of polar ice caps, both of which contribute to the causes of sea level rise. Increases in sea level can present problems to people living in coastal and low-lying areas, and can damage structures and beachfront property along the coast. Consequently, a sea level rise may impose economic costs on the United States – the costs of protecting coastal structures and the shoreline, or the lost value associated with abandoning such structures and property.

Early predictions of dramatic greenhouse gas-induced sea level rise have given way over the past decade to more modest expectations. High projections for the year 2100 reached more than 3.5 meters as late as 1983 (Hoffman et al., 1983), but they dropped to 1.5 meters in 1990 (IPCC, 1990), and converged slightly more than 1 meter by 1992 (IPCC, 1992). The mid-range best guess now stands between 38 and 55 cm by 2100 (IPCC, 1996). One recent estimate is presented in Table 7.1 (Wigley, 1995; Wigley and Raper, 1992). The oceans would continue to rise for centuries, even if concentrations were stabilized in the interim. Despite this, the highest best guess reported for the year 2100 is 40 cm.