New study suggests U.S. coasts may see greatest sea-level rise
MECHANICSVILLE, Va. — A study in last week’s edition of the journal Science suggests that sea levels may not rise as much as previously predicted under likely scenarios of human-caused climate change, but that the rising water levels will be devastating enough as it is.
Even more worrying for residents of the Atlantic and Pacific coasts of the United States, the rising levels will be 25 percent higher than in most other parts of the world’s oceans.
Most of the sea-level rise will come from the collapse of the West Antarctic Ice Sheet, which is already showing signs of breakup along its fringes. While previous studies had assumed a complete collapse of the ice sheet, the study by a team of British and Dutch scientists suggests a complete collapse is unlikely.
Much of the land portion of the West Antarctic Ice Sheet is locked in by ice shelves along the fringes of the continent. As the sea ice melts, the formerly landlocked ice can slide easily into the Weddell and Ross seas. A complete collapse of the ice sheet would trigger sea-level rises of 5 to 6 meters (16 to 20 feet).
Jonathan Bamber (Bristol Glaciological Centre, University of Bristol, Bristol, UK) and colleagues from the Delft University of Technology in the Netherlands and the University of Durham in the United Kingdom examined the bedrock beneath the ice sheet to determine how that might affect the amount of ice flowing into the sea.
Most of the vulnerable ice is located on bedrock that forms basins that lie below sea level. Where that bedrock slopes downward inland, the researchers assumed that the ice will start floating on the water that begins to fill those basins, forming ice sheets further inland that will likewise break up and trigger further collapse. On the other hand, Bamber and his associates assumed that ice grounded above sea level, or located on bedrock that rises inland, would remain intact. Under this scenario, global sea level rise would average only 3.3 meters (11 feet).
The volume of water added to the world’s oceans isn’t the only problem. The shift of mass from Antarctica to the oceans would affect regional variations in the the Earth’s gravity field, weakening the gravity field in the Southern Hemisphere and strengthening it in the Northern Hemisphere. The redistribution of mass would likewise affect the Earth’s rotation.
As a result, water would pile up in the northern oceans — especially along the Atlantic and Pacific shores of North America — as well as in the Indian Ocean. In those regions, the sea level rise would be as much as 25 percent greater than the global average. In other words, sea levels along the shores of the United States could rise by 4 meters (14 feet). While the full extent of the ice sheet breakup would take several centuries, sea levels could rise be nearly 1 meter (3 feet) by the end of this century.
Much of the Mid-Atlantic coast, with its gently sloping beaches, would not fare so well, even with the relatively small amount of sea level rise by the end of the century. By the time the full effect of the rising seas are felt, many major cities along the East Coast will be devastated.
For example, much of Hampton Roads, including large portions of Fort Eustis, Hampton, Newport News, and Poquoson — and virtually all of Fort Monroe Military Reservation, would be inundated. To the south, much of Norfolk, Portsmouth, and Naval Station Norfolk would likewise be inundated. As the largest navy base in the world, flooding there would have dire consequences on U.S. national security. Virginia Beach and surrounding areas would likewise be hard hit, with Virginia Beach’s waterfront hotel strip largely flooded.
Our nation’s capital region would also suffer. On the Virginia side of the Potomac, Alexandria’s waterfront as well as much of Ronald Reagan Washington National Airport would be underwater. Across the river, much of Bolling Air Force Base and Washington Navy Yard would be under water, as would Anacostia Park, East Potomac Park (including Hains Point). Portions of the Mall — including the Jefferson and Franklin Delano Roosevelt memorials and the Reflecting Pool — endangered. The Lincoln Memorial would likely survive as a small island. The edge of the Vietnam Veteran’s Memorial may remain above sea level, but waves would likely turn the walkway to the center of the monument into a small pond.
So, no matter whether there is 4 meters of sea level rise or 6 meters, the population in parts of the Mid-Atlantic region will suffer, and key cultural and environmental resources will likely be lost unless concrete action is taken to head off the specter of global warming.
— David M. Lawrence
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