Mid-Atlantic Air Protection

• Climate Change Effect on Sea-Level Rise
• The Impact of Climate Change on Estuaries and Barrier Islands
• Coastal Cities and Sea-Level Rise

There is broad consensus among scientists that rising concentrations of greenhouse gases are warming the atmosphere and oceans of the earth. The global effects of climate change are already apparent in the rapid melting of glaciers, the thawing of the permafrost, changing precipitation patterns, fringe forests dying and being converted to marsh and a rising sea-level. Regionally, some of the changes already apparent include more frequent flooding of low-lying land by storm surges and spring tides and marsh islands such as Big Piney Island in Rehoboth Bay disappearing as a result of erosion.

Climate Change Effect on Sea-Level Rise

The primary driver of such changes - the rate of relative sea-level rise - is affected by two things: the rate at which the sea level rises worldwide and the rate at which the land rises or subsides at particular coastal locations. As can be seen in the table below, regional rates of relative sea-level rise are already high compared to the global average of 1.7 millimeters per year because land is actually subsiding.

Rate of Relative Sea-Level Rise
Station	mm/yr	inches/yr
Portland, Me	1.91 ±0.09	0.0764 ±0.0035
Boston, Mass	2.65 ±0.10	0.1060 ±0.0039
Atlantic City, NJ	3.98 ±0.11	0.1592 ±0.0043
Baltimore, MD	3.12 ±0.16	0.1248 ±0.0063
Annapolis, MD	3.53 ±0.13	0.1412 ±0.0051
Washington,DC	3.13 ±0.21	0.1252 ±0.0083
Philadelphia, PA	2.75 ±0.12	0.1100 ±0.0047
Portsmouth, VA	3.76 ±0.23	0.1504 ±0.0091
Charleston, SC	3.28 ±0.14	0.1312 ±0.0055
Miami, FL	2.39 ±0.22	0.0956 ±0.0087
Table modified and reprinted by permission from Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region (rates in mm per year)

Much of Canada and inland portions of New England are slowing rising because of the (geologically recent) removal of the Wisconsin Ice sheet which covered those lands during the last ice age. Because the depression of those areas by the ice sheet also caused the Mid-Atlantic lands to bulge upward, the removal of the ice is causing the Mid-Atlantic to sink. This has resulted in current rates of relative sea-level rise roughly twice the global average.

Now, however, climate change is expected to substantially increase these already high relative rates by increasing the global rate of sea-level rise. Although the response of ice sheets to warmer temperatures can not be predicted, there is a consensus that sea level rise will accelerate as ocean waters expand and glaciers retreat. In 2007, the report by the Intergovernmental Panel on Climate Change, (PDF, 52 pp., 4MB, About PDF) projected a global sea-level rise of up to 59 centimeters during the next century assuming no acceleration discharge of ice by the Greenland and Antarctic ice sheets, and added that those ice sheets could add another 20 cm to sea level. More recent studies - taking into account recently observed acceleration of glacier melting and ice flows - have suggested a sea-level rise by the end of the century as being close to a meter or more (see Abrupt Climate Change: findings from the US Climate Change Science Program, Final Report)". Since this would take current relative sea-level rises in the region from a range of 3 to 4 mm per year (30 to 40 cm by 2100) to as much as 11 or 12 mm per year (110 to 120 cm by 2100), this would clearly have serious implications for the Mid-Atlantic region, given its thousands of miles of coastline, popular beaches, unique estuaries (e.g., the Delaware and Chesapeake Bays), wide variety of critical habitats, and coastal cities.

The Impact of Climate Change on Estuaries and Barrier Islands

A report released in 2009, Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region attempted to project the effects that various increases in the rate of sea-level change would have on the Mid-Atlantic Region (which was defined as including Region 3 states plus New York, New Jersey, and North Carolina). The study analyzed 3 scenarios:

a rise in relative sea-level at the current rate    (an average 3 to 4 mm annual rise)

a rise at the current rate plus 2 mm per year    (a 5 to 6 mm annual rise)

a rise at the current plus 7 mm per year
   (a 10 to 11 mm annual rise)

While the results of the report are too complex to summarize here, it is worth looking at two maps depicting how wetlands and barrier islands in the region could be affected under the three scenarios. As the map on the right shows, while only a few wetland areas are likely to be lost or threatened under current rates of sea-level rise (blue, red and orange), most will be lost or threatened under Scenario 3 (all but dark green). Since wetlands serve many functions - flood control, a buffer from storm surge, a way to protect water quality, bird and animal habitat, feeding grounds for migrating shore birds, fish spawning grounds etc - their loss will have important economic and social consequences for the region.

 

Similarly, while few barrier islands are likely to be lost or seriously threatened under Scenario 1, the majority are likely to undergo major changes due to erosion, overwash, and/or island breaching under Scenario 3. Areas denoted with a "T" may also cross a threshold where rapid barrier island migration or segmentation will occur. For those areas (e.g., Ocean City, Md.) that have been transformed from sparsely populated areas into highly developed, year-round cities, there will undoubtedly be large economic costs incurred attempting to prevent such damage. For those barrier islands in Maryland and Virginia, the costs will be largely environmental with critical bird and fish habitats either having to migrate inland or being lost.

The two maps only consider the direct effects of sea level rise. An EPA-funded study examined how those society's adaptive response to sea level rise might alter those impacts. The authors met with officials from 130 local governments to determine which lands are likely to be protected from rising sea level and which lands would be available for the inland migration of wetlands under existing policies. Based on the input from the local officials, the authors estimated that 60 percent of the land vulnerable to sea level rise is likely to be developed and protected, and hence not available for the inland migration of coastal wetlands. State and local government are committed to maintaining almost all barrier islands. The study was published in the journal Environmental Research Letters.

 

Coastal Cities and Sea-Level Rise

Although communities situated close to the ocean are most vulnerable to beach erosion and hurricanes, the vast majority of low-lying lands and tidal shores in the Mid-Atlantic are along estuaries. In fact, since twelve of the fifteen largest cities (by population) in Region 3 are on either the ocean or a tidal river, this means the effects extend much more broadly than is generally supposed. In addition to those few cities, such as Virginia Beach and Ocean City, that are vulnerable to the most dramatic, direct effects of sea-level rise such as having structures being swept away by ocean waves, there are also other cities, such as Philadelphia, Baltimore, Washington and Norfolk, that are vulnerable to less dramatic effects such as increased flooding and the gradual submergence of low lying lands.

In Philadelphia, for example, approximately 10 square kilometers of lands is less than one meter above high tide, and there is also a low area just outside the city limits near Philadelphia International Airport. As sea level rises, these lands will require increasingly aggressive flood prevention activities. Moreover, the rising sea level and increasingly severe droughts are likely to allow saltwater to advance further upstream in the Delaware River, possibly threatening the city's freshwater intake at Torresdale. More generally, since large cities are more densely populated and have higher replacement costs for land, structures and other infrastructure, the costs associated with such flooding can nevertheless be large.

In Washington, DC, for instance, only a small proportion of the highways are vulnerable to increased future flooding, but given the costs of highways contruction in such an urban area, the associated costs are potentially quite high. Similarly, in Baltimore, only 3 percent of the land is in the coastal floodplain, but since this land includes the Inner Harbor and the Fells Point Historic District costs will inevitably be high.

To find a person who can provide more detailed information regarding climate change issues go to EPA Regional Climate Change Contacts page.