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Chesapeake Bay
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Rising Seas, Changing ClimateWhen Captain John Smith and his crew sailed up Chesapeake Bay on the mid-Atlantic coast in 1608, they passed a large, low-lying island in the upper middle reaches of the bay, about 34 nautical miles south of today's Baltimore. Poplar Island, as it became known, covered more than 1,400 acres in Smith's time. The island eventually supported a small town, and later — in the 1930s and 1940s — an exclusive retreat for politicians, including Presidents Franklin D. Roosevelt and Harry Truman.
Impacts at a Glance
- Chesapeake Bay on the mid-Atlantic coast is rising twice as fast as the global average rate of sea level rise.
- Chesapeake Bay and the sea around Assateague Island are likely to rise 27 inches by 2100, and most likely will keep rising after that.
- Chesapeake Bay's islands are being submerged and eroded by the rising seas.
- Sand beaches and marshes along bay shores are vanishing in those developed areas where people armor the shoreline against the sea.
- Storms will do more damage as the sea level rises.
- Warmer or more saline waters could encourage the spread of oyster disease and affect fish in Chesapeake Bay.
- Global warming could have a major impact on the region's bird life, including migratory waterfowl that overwinter in Chesapeake Bay.
- Sea level rise might cause Assateague Island to become narrower and move landward.
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If Captain Smith could repeat his Chesapeake voyage today, he might be surprised to see what remains of Poplar Island. Instead of the substantial body of land he encountered in 1608, Poplar Island now consists of a small group of islets that together measure less than 5 acres. Dead trees rise from the water to mark where land stood only a few years before.
Rising seas and heavy erosion have flooded and eaten away more than 99.5 percent of Poplar Island during the past 150 years. With the shoreline retreating by more than 13 feet annually, the island's remnants would have vanished under the sea by the year 2000 if it weren't for a $427 million restoration program launched in 1998 by a coalition of federal, state, and nongovernmental agencies.
Poplar Island's story is not unique. The University of Maryland's Laboratory for Coastal Research found that at least 13 islands in Chesapeake Bay have disappeared entirely since the region was first described and mapped by Europeans. Several other islands may be inundated as the sea continues to rise. Smith Island (named after John Smith) near the mouth of the Potomac, supports three small towns and a population of close to 400 people. Since 1850, the formerly wooded island has lost 30 percent of its land, and has split into several mostly marshy islands. Unless fill material is brought in to elevate the remaining dry land, Smith Island will be lost to the sea during the next century. Tangier Island is also vulnerable. Many factors also threaten the way of life of the watermen and crabpickers that inhabit these two islands, including declining crab and oyster harvests and decisions by young adults to move off these islands to communities that are less isolated; but erosion and sea level rise threaten the islands themselves.
Why is the sea rising? Global warming causes water at the surface of the ocean to expand and adds sizable quantities of freshwater runoff from melting glaciers. In areas where the land is sinking due to changes in the Earth's crust, the effects of rising seas are even more pronounced. In the Chesapeake Bay area, scientists believe global warming accounts for about 2 to 6 inches of the 12 inch sea level rise that has occurred during the past 100 years. Natural geologic subsidence of land in response to the melting of the ice sheet that covered much of North America during the last ice age contributed another 6 inches to sea level in the past century. Scientists are unable to confidently attribute up to 4 inches of the rise over the last century: Possible causes include a delayed response to the global warming that took place over the last several thousand years, natural climatic fluctuations, and compaction of sediment from groundwater withdrawals.
EPA estimates that with additional global warming and continued subsidence, sea level in the Chesapeake Bay area probably will rise another 8 inches by 2025, 13 inches by 2050, and 27 inches by 2100, compared with the level in 1990. Such a rate of sea level rise would be approximately double that of the preceding century. The rise is expected to be somewhat faster during the second half of the 21st century than the first half, because glaciers would be melting more rapidly due to the warmer temperatures. By the year 2100, sea level is likely to be rising at more than twice the current rate. There is even a small risk — a 5 percent chance based on current models of glacial and oceanic processes — that the sea will rise as much as 44 inches by 2100. It is also possible that the rate of sea level rise will not accelerate for several decades, if at all.
For the past 5,000 years, the average rate of sea level rise in Chesapeake Bay was approximately one inch every thirty years. By the end of the 21st century, sea level may be rising one inch every three years.
Marshes and Beaches at RiskAn accelerated sea level rise could eliminate most of Chesapeake Bay's marshes and beaches, especially if shores are armored to prevent their landward migration. The loss of these habitats in turn would affect birds, fish, terrapins, and other wildlife. The future Chesapeake Bay might lose some of its charm for the thousands of kayakers, boaters, anglers, windsurfers, and birders who spend time on and around the bay each year.
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"We are once again at the threshold, as we were in the 1970s, facing the decline of the Chesapeake Bay."
- Sarah J. Taylor-Rogers, Assistant Secretary,
Maryland Department of Natural Resources, October 18, 1996 |
Salt marshes can keep up with moderate increases in sea level but may be drowned if the sea rises faster than sediments and peat can build up the marsh. In low-lying areas like the Eastern Shore or Virginia's Back Bay National Wildlife Refuge, new marsh develops naturally as rising seas flood the land. Similarly, beaches are able to migrate inland. But many Eastern Shore residents are armoring their property against the sea by building sea walls, bulkheads (vertical walls usually made of wood), and revetments (rocks piled along the shore). These structures prevent marshes and beaches from moving inland as the sea rises. Since 1980, Chesapeake Bay residents have built bulkheads and revetments along 350 miles of shoreline. If this trend continues, many of the bay's beaches and marshes will be lost, squeezed between the rising tide and the armored shore.
Captain Smith might be thoroughly astonished by a sail through Chesapeake Bay in the year 2100. He would hardly recognize the landscape before him. If present trends continue, the "many isles" described in his writings will have vanished, along with most of the marshes and beaches.|
| Chesapeake Bay Region
Red areas indicate some of the areas that could be flooded at high tide if global warming causes sea level to rise 2 feet by 2100.
Blue areas that might be inundated over a period of several centuries.
The indicated areas account not only for the effects of global warming, but also for other effects such as tidal variations and land subsidence. Source: Titus and Richman (2000)
Approximately 1000 square miles of land in Maryland and Virginia could be inundated by the tides if sea level rises two feet. |
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