Study finds sea level rise accelerating along Atlantic coast

Sea levels are rising faster along the Atlantic coast - including in the Chesapeake Bay - than elsewhere around the world, and the increase appears to be accelerating, according to federal scientists.

In a paper published online in Nature Climate Change, the U.S. Geological Survey reports that sea level rise is increasing three to four times faster than globally along a heavily-populated 600-mile stretch of coast from Cape  Hatteras, NC to north of Boston. 

Since 1990, the rise has increased 2 to 3.7 millimeters per year in the "hotspot," as the federal scientists call it, compared with a global increase of 0.6 to 1 millimeter per year.  That hotspot includes the Chesapeake Bay, according to USGS oceanographer Asbury H. Sallenger, lead author of the report.

"If you raise sea level across the mouth of the Chesapeake Bay, it's going to increase the overall level of the Chesapeake Bay," he said.

Climate change causes sea level to rise as land-based ice near the earth's poles melts, but also as rising temperatures cause the ocean water to expand.  But researchers expect sea-level rise to vary around the globe because of various factors, including ocean currents, differences in sea-water temperature and saltiness and the earth's rotation.

The trio of USGS scientists found that tide gauge data over the past 60 years tend to confirm computer models that have forecast an increase in sea level rise along the Atlantic.  The models have hypothesized that ocean currents running along the Atlantic coast are slowing, resulting in increases in sea level, Sallenger said.

Analyzing sea-level rise rates can help scientists understand how and why the beaches along the coast are changing, Sallenger said. The information could help predict the submergence of salt-water marshes along the coast, and also could assist coastal communities to prepare for the encroaching water.

The sea level along the Maryland coastline has risen at a rate of 3 to 4 millimeters a year over the past century, the state's climate change commission reported in 2008.  That's nearly twice the global average rise of 2 millimeters a year.  About half of that increase has been attributed to the subsidence, or sinking, of the land bordering the water.

The USGS study looks beyond those absolute increases in sea level to the relative rates of increase.  And along the Atlantic "hotspot," the USGS team found the rates vary.

The largest increase in rates of sea level rise were seen in the Norfolk area, about 6 millimeters per year, according to Peter A. Howd, another USGS oceanographer involved with the study.  The acceleration around Baltimore was in the middle of the hotspot distribution, Howd said."Cities in the hotspot, like Norfolk, New York and Boston already experience damaging floods during relatively low intensity storms," according to Sallenger.  "Ongoing accelerated sea level rise in the hotspot will make coastal cities and surrounding areas increasingly vulnerable to flooding by adding to the height that storm surge and breaking waves reach on the coast."

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