Why we did this report

The sea is rising. Tidal gauge measurements from around the world confirm this fact. In the last 100 years, global sea level has risen about 7 inches (IPCC best estimate). Along much of the U.S. coast, sea level rise has been greater -10 to 12 inches in the last century. Over the last 15 years, concerns that the rate of sea level rise may accelerate led coastal decision makers to seriously consider how to respond to this problem.

A series of reports have projected future rates of sea level rise, likely environmental and economic impacts, and possible response strategies. In 1982, EPA first began to project sea level rise, and first published estimates in 1983 in Projecting Future Sea Level Rise. Between 1984 and 1989, EPA conducted the first assessments of potential response strategies for New Jersey, Maryland, Charleston, the Delaware River Basin, Galveston, and San Francisco. Since the publication of the 1980 EPA Report to Congress, the Agency has actively participated in the IPCC assessment process.

Other agencies and organizations have also studied this issue. In 1987, the National Research Council (Committee on Engineering Implications of Changes in Relative Mean Sea Level) issued a report that concluded "The risk of accelerated mean sea level rise is sufficiently established to warrant consideration in the planning and design of coastal facilities." The report recommended "that appropriate statistical techniques

be applied to develop a probability distribution associated with sea level rise through the year 2100 and that all updated projections include such information." In addition, the report noted that while it may be some time before exact estimates of sea level rise are available, the risks associated with a substantial rise should not be disregarded.

Many decisions that the Federal, state, local and private sectors are making today regarding investments in coastal structures are sensitive to local sea level rise. For example, barriers have been built to protect coastal cities from flooding during storm surges. Engineers design these structures to deal with storms of specified design magnitude. The safety factors of these structures will be reduced as sea level rises. Maintaining the desired level of safety requires an explicit consideration of the probability distribution of sea level rise.

Statutory requirements have also resulted in institutional needs for sea level rise probability information. For example, the Coastal Zone Management Act requires states to plan for accelerated sea level rise from a changing climate. Similarly, the Water Resources Development Act of 1985 requires the Army Corps of Engineers to determine how to address accelerated sea level rise. Congress requires FEMA to assess the implications of sea level rise for the Flood Insurance Program. At the state level, various State Beach Management Acts require the type of probability information contained in the EPA report. In addition, ongoing plans to address land loss in states

such as Louisiana, South Carolina, and Maine, already recognize accelerated sea level rise as a factor that could alter the best response policy.

The cost of preparing for sea level rise may be small compared to the eventual costs if the sea rises more than allowed for in the initial project design. This is likely to be true for structures which are ill-suited for retrofitting. For example, coastal buildings such as beach-front hotels and shopping centers would be vulnerable to a rise in sea level. A one foot rise in sea level may put the entire investment in the development in jeopardy. The prudent design might include an extra foot of elevation or a horizontal setback to safeguard against expensive reconstruction. Similarly, when offshore oil-drilling platforms are being built, engineers now add an extra meter to platform height as an insurance policy to protect against sea level rise. They don't know for sure that sea level is going to rise by a meter, they do know, however, that it's much cheaper to build the platform one meter higher than to risk losing the whole platform.

The purpose of the EPA report is to provide this information to decision makers. It does this by translating information from the IPCC and others into a form that is more directly usable to coastal decision makers. That is, the EPA report contains probability-based projections which can be added to other local information (e.g., tide-gauge

measurements) to estimate future sea level rise at a particular location. For example, in Boston, MA, there is a 50 percent chance that sea level will rise 22 inches by the year 2100, a 10 percent chance of a 34 inch rise, and a 1 percent change of a 48 inch rise.

The EPA report also allows decision makers to determine when a specified amount of sea level rise is likely happen. For example, in Washington DC, there is a 1 percent chance of a one foot rise in sea level by 2025, a 45 percent chance by 2050 and a greater than 90 percent chance by 2100.

Finally, estimates of sea level rise vary substantially by locality. For example, by 2100 there is a 50 percent chance that the sea will rise: by 13 inches in Los Angeles, CA; by 20 inches in Miami Beach, FL; by 27 inches in Atlantic City, NJ; by 38 inches in Galveston, TX; and by 55 inches in Grand Isle, LA. This information can help coastal zone managers and others make better informed and more cost-effective decisions to protect coastal areas and structures, personal property, and coastal wetlands.

EPA results and consistency with IPCC estimates

I would like to note the good agreement and general consistency between the EPA and IPCC sea level rise estimates. The differences lie in that the EPA report estimates probabilities associated with various increases in sea level, whereas the IPCC report provides a lower, upper and best estimate, not in the overall fining of sea level rise.

The EPA report estimates a 50% chance of sea levels rising 18 inches (45 cm) by the year 2100. The best estimate by the IPCC is for 19 inches (49 cm). IPCC also reports a "high" estimate of a 34 inch (86 cm) rise. The EPA report attaches probabilities of

10% and 1%, respectively, to its estimates of a 29 and 44 inch (75 cm and 112 cm) rise, bounding the IPCC high estimate. We are in close agreement with IPCC's "low" estimate of an 8 inch (20 cm) rise, for which we estimate a "high likelihood" probability of 90%.

Both the IPCC and the EPA reports note that the latest central estimates of sea level rise are lower than previous estimates, primarily due to lower estimates of global temperature change. We should also keep in mind that the range of uncertainty which surrounds these estimates is narrower. The science is improving, increasing our confidence in estimates of future sea level rise.

I would like to stress that there are significant impacts even with these newer estimates. For example, a one-foot rise in sea level in 2100 would result in the following impacts to the Atlantic and Gulf coasts:

20-30% of coastal wetlands would be lost;

Sandy beaches would be eroded 100-150 feet;

Along developed estuarine shores such as the Chesapeake Bay, most beaches

would be replaced by bulkheads;

Along ocean shores such as the Outer Banks, beaches would require

nourishment and/or beach homes would be lost; and