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PRI's Environmental News Magazine

Surf’s Up, America

Published: August 11, 2012


By Jeff Young

Sea Levels Will Likely Rise Faster Than Global Average Along Parts Of Both U.S. Coasts

Two new reports say sea levels along vast stretches of the U.S. Atlantic coast and California will likely rise at rates faster than the global average. Some 600 miles of the Atlantic coast—from North Carolina’s Outer Banks north to Boston—is already experiencing sea level rise three to four times faster than the world average.

"Many people mistakenly think that the rate of sea level rise is the same everywhere as glaciers and ice caps melt,” U.S. Geological Survey Director Marcia McNutt said in a USGS release. “But other effects can be as large or larger.” The new reports, from the USGS and the National Research Council (NRC) of the National Academies of Science, looked carefully at factors like differences in land movements, strength of ocean currents, water temperatures, and salinity changes, all of which can cause the sea’s highs and lows to vary from place to place.

The USGS report, published in the journal Nature Climate Change, focused on the East Coast, which scientists call a “hotspot” of sea level rise. The stretch of coast that includes New York, Norfolk, Va., and Boston has already experienced far higher than average sea level rise. The report finds that by the end of the century sea levels there could rise an additional 8 to 11.4 inches on top of the projected global rise.

The NRC report looked at the West Coast. At the high end of the estimates California could see as much as a foot of sea level rise (30 cm) by 2030. Sea rise could be double that by mid century (60 cm) and as much as 5.5 feet (167 cm) by 2100. (The estimates include a broad range of uncertainty with the lowest end at just 1.5 inches at 2030.)

The story could be different for Washington and Oregon, where geologic forces are pushing the land upward, meaning the sea level rise they experience will be less. Unless it isn’t. There’s a wildcard, and that’s earthquakes. A big quake could bring the land level down for the Pacific Northwest, increasing the impact of sea level rise.

The wide range in the estimates and the many variables involved underscore the difficulties in planning around sea level rise. State agencies in California, Oregon and Washington joined federal agencies in asking the National Academies for the best available science on rising sea levels in the coming decades. The projections can help guide decisions about coastal development, infrastructure and spending to adapt to climate change.

The stakes are high. The NRC report noted “San Francisco International Airport could flood with as little as 40 centimeters of sea-level rise, a value that could be reached in several decades.” And the additional flooding possible from storm surges and very high tides greatly increases with sea level rise. In the East coast “hotspot” many towns and cities already experience damaging flooding from relatively low intensity storms, according to USGS report co-author and oceanographer Asbury Sallenger. “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,” Sallenger said.

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