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Forum on Sea-Level Rise and Coastal Disasters

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The late Quaternary geologic record from various sources shows that sea level has fluctuated by more than 100 m over the past 20,000 years in response to climate warming and cooling caused by complex and largely unknown factors. In general, sea level has been rising, but at highly variable rates temporally and spatially. This worldwide, eustatic sea-level rise results from such factors as melting of continental glaciers and ice sheets and expansion of ocean waters heated by global warming. In addition to climate, sea level is influenced by the constant vertical motion of the Earth's crust due to tectonic stresses and isostatic adjustments to differential loading and unloading from massive glaciers during the most recent Pleistocene glacial period. The combination of eustatic sea-level changes and crustal elevation changes yields relative sea level. Changes in long-term sea level are responsible for driving the Holocene marine transgression, in which coastal landforms have been inundated and eroded by waves and currents, resulting in landward migration of coastal barrier islands and wetlands and yielding the present coastal geomorphology.

Such historical data as tide-gauge records, corrected for change in land elevation, show that eustatic sea level has risen an average of about 20 cm over the past century. Relative sea-level rise has averaged about 30 cm, but regions undergoing subsidence (mostly natural, some anthropogenic), such as the Mississippi River delta in Louisiana and parts of Chesapeake Bay, are undergoing relative sea-level-rise rates of more than 10 mm/yr. The combination of rising sea level and increasing human population density and development along the coasts is cause for growing concern. In addition, there is scientific consensus that sea level will continue to rise into the next century and its rise is likely to accelerate. Models suggest various rates of rise over the next 100 years, but the "best midrange estimate" based on the 2001 Intergovernmental Panel on Climate Change (IPCC) report is a sea-level rise of approximately 50 cm over the next century. Sea-level rise of this magnitude has grave implications for all ocean-coast regions of the United States and especially for deltaic regions and island nations around the world.

To facilitate communication and exchange of ideas between scientists, planners, and policy makers on potential natural-disaster issues, such as sea-level rise, the National Academy of Sciences (NAS) hosts open and public forums several times a year. The most recent meeting was held in Washington, D.C., on October 25, 2001, where Virginia Burkett (USGS, National Wetlands Research Center, Lafayette, LA) and Jeff Williams (USGS, Woods Hole, MA) were invited speakers and participants.

Virginia gave a case study of the alarming situation facing New Orleans: much of the city is as much as 4 m below sea level. It is protected to a limited degree by dikes ringing the city but is highly vulnerable to continued subsidence, accelerating sea-level rise, and storm surges as high as 5 m.

Jeff spoke as part of a panel of Federal- and State-agency scientists on the processes and factors affecting coastal change and the public-policy options available for dealing with coastal change, and he summarized ongoing and planned USGS research aimed at providing coastal-science information for knowledge-based public policy.

Related Web Sites
Natural Disaster Forums
National Academy of Sciences (NAS)
Coastal & Marine Geology Program
U.S. Geological Survey (USGS)
National Wetlands Research Center
U.S. Geological Survey (USGS)

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Honduras Coral Reefs

Black Carbon

Miami Canal Surveys

Cape Cod Lakes

Outreach African Dust Lecture

Rock Stories

Falmouth, MA Public Schools

WHFC Web Site

Meetings Coral Reefs

Sea-Level Rise & Coastal Disasters

Chesapeake Bay

Water Quality

Restoring Louisiana's Coastal Ecosystems

ArcGIS 8.1

Marine Technology

Staff & Center News Two New Postdocs

Student & Visiting Scientist

Data Management

WHFC Visitors

Cape Cod Marathon

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