Sea-Level Rise Implications for Coastal Regions

Sea-level rise, a dominant driving force of change for coastal regions, is becoming increasingly important as a hazard to humans and urban areas in the coastal zone worldwide as global climate change takes effect. The geologic record shows that sea level, due to past natural climate factors, has been highly variable, as much as 6-8 m higher than present during the last interglacial warm period and 130 m lower during the last glacial period. Sea level was fairly stable for the past 3,000 years until about the mid-19th century. During the 20th century, sea level began rising at a global average rate of 1.7 mm/yr. The current average rise rate is 3.1 mm/yr, a 50% increase over the past two decades. Many regions are experiencing even greater rise rates due to local geophysical (e.g., Louisiana, Chesapeake Bay) and oceanographic (Mid-Atlantic coast) forces. A few regions experience rise rates less than the global average due to land uplift. Observations show the increase of carbon emissions since the Industrial Revolution has increased global mean temperature of the air and ocean, which is responsible for sea-level rise due to ice sheet melting and steric expansion, and many related environmental changes. Sea-level rise, with high regional variability, is exhibiting acceleration and is expected to continue for centuries unless mitigation is enacted to reduce atmospheric carbon. Low-lying coastal plain regions, deltas, and most islands are highly vulnerable. Adaptation planning on local, state and national scales for projected sea-level rise of 0.5-2 m by A.D. 2100 is advisable. Sustained global rise in sea level of 4 m to as much as 8 m is possible, but not likely until well after A.D. 2100.