As greenhouse gases build-up in our atmosphere, one of the most likely impacts of climate change is rising sea levels. Sea level will rise because warm water expands and glaciers and ice sheets melt, adding water to the ocean. Sea-level rise, already occurring and projected to occur 2-4 times faster in the 21^st century, could inundate low-lying areas of the Northeast, many of which include densely populated locations. For example, 38% of the Mid Atlantic Region (MAR) population lives in its coastal counties -- accounting for only 19% of its land area. Five of the MAR's six largest cities (Philadelphia, Baltimore, Washington, Norfolk, and Richmond) are in its coastal zone.

Changes in the strength, number, and track of future storms are as yet uncertain for the Northeast. However, the potential for altered storm locations and intensities, combined with rising sea levels, could result in increased damage due to more intense storm waves. There is also the potential for fewer and or weaker storms. The threat of an increase in storm intensity or frequency would obviously pose significant social and economic concern to coastal residents of this region. Other potential effects of sea-level rise include erosion, inundation, saltwater intrusion, wetland destruction, and impacts on the biology and ecology of coastal systems. These potential impacts are explored below.

Sea level is projected to rise substantially along the coastal Northeast. Currently, the average rate of sea-level rise along the Atlantic coast ranges from just over 3 inches per century around Boston, Massachusetts (the coast along Cape Cod could be significantly higher), to approximately 14 inches per century in parts of Virginia. [The difference is that in some places the land is rising more than other places as a result of glaciation in the Northeast more than 10,000 years ago.] Projections are that the component of sea-level rise related to global sea level change (4 to 8 inches during the 20^th century -- not land movement) could increase by 2-4 times during the 21^st century. Because different rates of sea-level rise are experienced in different locations depending on local rates of subsidence (settling) or uplift of the land, estimates of future relative sea-level rise must be made locally.

An EPA study suggests a 50% chance by 2100 of a 19-inch sea-level rise in Portland, Maine. The same study suggests that 1,000 square miles along the coastal Northeast are at risk from a 20-inch rise in sea level. For a 24-inch sea level rise (within the range of the estimates for the year 2100), about 22,000 acres of coastal land on the shoreline of Delaware would be lost. Those 22,000 acres would include 21% of the newly forming wetlands in the region. Although flooding would likely cover only 1% of Delaware's highly developed area, this land is economically important. Impacts would become larger because of any additional development allowed to occur between now

Although erosion rates are difficult to predict because they depend on topography and geology, applying the ‘Bruun rule' (a calculation to assess potential erosion rates) and other analytical processes suggests that each foot of sea-level rise could erode 50 to 100 feet of shoreline in New Jersey and Maryland. Reports indicate that about 33 acres of land are already lost on Massachusetts' Cape Cod each year -- 73 % is due to inundation and 27% to active erosion. The local topography (e.g., land elevation, sand or rock, etc) is responsible for determining how much and how fast the inland areas are covered by a rising sea. If not interfered with by human activities, much of the submerged land is transformed into salt marsh. Erosion from inland areas provides sand for barrier beaches. That sand then moderates the erosion process and provides storm and flood protection for surrounding lands.

If climate change increases the rate of sea-level rise, coastal wetlands would be extremely vulnerable to submergence and erosion. According to the same EPA study, many wetlands would be submerged by the 20-inch rise in sea level. However, if the zone near the new waterline is not developed or blocked off by using seawalls or other barriers against sea-level rise, some wetlands could be shifted inland with the rising sea level, creating new wetlands to replace those being lost. Other areas could become open waters, as has happened with Maryland's Blackwater National Wildlife Refuge.

Another result of rising sea level is that saltwater, vital to the health of an estuary, would migrate upstream unless freshwater runoff is increased. This would cause a shift of marine ecosystems upriver. Because these ecosystems often are adapted to specific tidal ranges, species and whole ecosystems of the Northeast could be lost if the upstream conditions are not suitable for such migration or the particular species is unable to shift along with the sea level. Sea-level rise could also result in crowding-out species that are now in those spots, if there isn't suitable upland or upstream habitat for them to move to. If, however, the shoreline is developed to prevent erosion or submergence or is otherwise unsuitable (up against a cliff), then inter-tidal habitat shifts (described above) that might have occurred because of sea-level rise would be prevented. Preserving inter-tidal habitats is a significant concern, because the wetlands and other inter-tidal areas (e.g., mud flats) are important nursery grounds for many species of coastal and anadromous fish (fish that live in the oceans and breed in freshwater e.g., shad) and shellfish. These areas are also important feeding grounds for many migrating waterfowl. Two of the largest concentrations of migrating shorebirds in the Western Hemisphere are found in the Chesapeake and Delaware Bays. During the winter, Chesapeake Bay acts as home to about a million ducks, geese, and swans. Thousands more shorebirds use the area as a stopover point to feed during their migrations.

Saltwater intrusion could convert some areas of coastal freshwater wetlands to salt marshes. Groundwater would also be affected, as brackish (salty) water infiltrates aquifers that supply drinking water to coastal communities. This occurred in the Delaware River estuary during the drought of 1964. Although that saltwater intrusion occurred as a result of low freshwater flow, salt water has been observed in the Potomac-Raritan-Magothy aquifer system since that event. This aquifer supplies the greater Camden, New Jersey area and is vulnerable to future saltwater intrusion because the aquifer is recharged by the freshwater portion of the Delaware River estuary. Low freshwater flow, a rise in sea level, or both could contribute to future episodes of saltwater intrusion.

In addition, as sea level continues to rise, the amount of the Northeast's coastal area subject to flooding from storms will increase, especially in low-lying areas. Increases in sea level can cause dramatic changes, because higher sea levels would provide a raised base from which storm waves could sweep inland, allowing for greater and more spread-out damage than would occur with lower sea levels. Even if storm strength were not increased, higher sea levels are very likely to cause increased damage, making the consequences seem like they were from a stronger storm.

As sea-level rises along the Northeast coast, those living in coastal communities are likely to face increased exposure to compromised ecosystems, impacted water supplies, flooding due to storm events, loss of property -- both public and private -- through erosion and inundation, and risk to life. All of these impacts present overlapping social and economic costs, which are addressed jointly here.

Rising sea levels increase the damaging effects of storms. The past two decades have seen storms resulting in costly insurance claims. For example, between 1978-1998 for coastal counties in New Jersey, Delaware, Maryland, and Virginia, there were $21 billion dollars in National Flood Insurance policies in effect. During that same period, only $81 million dollars was collected in revenue but $327 million dollars were paid out -- $138 million of that was repetitive -- meaning that taxpayers are paying for damage to the same properties from one storm after another. Nearly all of the increase in insurance claims over the past 50 years is because of more people and structures being located in unsuitable locations rather than due to increases in storm frequency or strength. However, sea-level rise makes the same intensity storm go farther inland, thus creating more damage.

One method of protecting valued areas is to replenish beach sand. An average cost of a cubic meter (about 1.3 cubic yards) of sand is about $5 (in year 2000 dollars). A New Jersey policy of beach replenishment that is being considered has been estimated to cost $60 million per mile, totaling $9 billion over 50 years.

Sea-level rise also would affect the region's fishing industry because a sea-level rise that is large enough to damage coastal wetlands could cause a decline in coastal fisheries, that depend on wetlands as breeding habitat for many fish species. Thirty-two percent of the Acadian-Boreal (Cape Cod, Massachusetts, and north) fisheries and 87 % of the Chesapeake Bay fish are estuarine-dependent. The Acadian-Boreal and the Virginian-Mid-Atlantic (Cape Cod to Cape Hatteras, North Carolina) fisheries together constitute 18 % of our nation's coastal fisheries, for a total estimated value in 1990 of $750 million.

For bird watchers and other outdoor recreators, wetlands are an important draw and the economic boost that they provide to the region has an important seasonal component. For example, Chesapeake and Delaware Bays provide a temporary home, during various parts of the year, to two of the largest concentrations of migratory shorebirds in the Western Hemisphere.

Some of the economic costs of sea-level rise damage to wetlands are very difficult to estimate. Wetlands perform functions that are important ecologically but are also important to the inland areas that they border. For example: wetlands buffer the coasts from storms by dissipating wave energy; wetlands slow erosion; wetlands moderate flooding by soaking up water (like a sponge) during times of high water; and wetlands clean the water by slowing runoff and absorbing nutrients, sediments, and pollutants before they reach the coastal waters. It is difficult to predict precise impacts in such a complex and interconnected ecosystem as wetlands. They are likely, however, to suffer negative effects from sea-level rise and the other stresses to which they are already subjected.

The ultimate consequences of sea-level rise to the built or human environment cannot be easily foreseen. Using an example from another region (Metro East Coast - MEC) to make the point: A nor'easter storm in 1992 showed the vulnerability to rising sea levels of the MEC transportation system. The storm, on December 11-12, not even of hurricane strength, resulted in some of the worst flooding and highest winds on record for the area. Critical transportation systems in the City (including JFK airport and the Lincoln tunnel) are only 7-20 feet above present sea level. Had the storm waves been only 1 to 2 feet higher (as could happen with rising sea levels), massive inundation of rail lines and subway tunnels in New York City could have resulted. The costs associated with such a flooding event could have been tremendous. Such unusual historical events can illustrate potential areas of vulnerability in coastal infrastructure as the sea level rises.

At least three strategies are available to cope with the projected effects of sea-level rise in the Northeast. Strategies include: 1) retreat from advancing seas, 2) accommodate changes imposed by a higher sea level, and 3) protect areas/structures from sea-level rise. All three coping strategies could be more appropriately considered through information efforts that help concerned parties cope with the prospects for potential coastal changes and to avoid putting themselves in harms' way to begin with. For example, all stakeholders should be informed about the risks of building in hazard-prone areas and the potential for changes in storm frequency, intensity, and sea level.

A strategy of retreat is appropriate if the objective is to allow ecosystem migration. Retreat could include the following actions:

• Establish regulations in building codes that require structures vulnerable to inundation to be moved if threatened (such codes are in place in Maine and South Carolina for example);
• Buy coastal land and prohibit its development;
• Account for projected sea-level rise in planning and development, and enact anticipatory building codes;
• Discourage development in especially vulnerable areas by ending the subsidy for coastal flood insurance; and
• Provide for moving easements to allow the public access to the changing shoreline.

Accommodation could entail the following steps:

• Regulate building development by instituting stronger and more appropriate building codes and restricted locations; and
• Develop and offer incentives to encourage informed decision-making about coastal hazards.

A strategy designed to protect coastal lands can be appropriate along economically valuable shorelines that have been identified as high priority for protection. Such efforts could include:

• Nourishment of protective beaches; and
• Construction of bulkheads and sea walls.