Goddard Earth Sciences Update 18 August 2000
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GODDARD EARTH SCIENCES UPDATE AUGUST 18, 2000
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Dr. Vincent Salomonson, Earth Sciences Director
Goddard Space Flight Center
Greenbelt, MD 20771 (301) 614-5634
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Goddard Earth Sciences Update” is a weekly bulletin to keep management apprised of the
latest accomplishments of Goddard’s Earth Sciences Directorate. This newsletter is also
accessible at http://www.gsfc.nasa.gov/ Please forward comments or suggestions to:
Lynn Chandler (301) 614-5562 or Debra. L.Chandler.1@gsfc.nasa.gov
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In this Issue: Rising Seas: A View from New York City
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Rising oceans will eat away at the nearly 2400 km of shoreline encircling the
greater New York City metropolitan region — presently home to 19.6 million people. Sea
level has already climbed around 27 cm in New York City and 38.5 cm along the New
Jersey coast during the 20th century. These local rates exceed the global average of 10-25
cm/century because the East Coast is slowly sinking, as the earth’s crust continues to
readjust to the removal of the ice from the last glaciation, around 15,000 year ago. But
present rates of sea level rise could accelerate severalfold, as mountain and polar glaciers
melt and upper ocean layers heat up and expand, due to global warming.
How would rising sea levels affect the New York City area? A team of
scientists from the Center for Climate Systems Research, Goddard Institute for Space
Studies and Columbia University has investigated these issues as part of the Metropolitan
East Coast (MEC) Assessment. Future sea levels are estimated by extrapolating
historical trends and using two global climate model (GCM) projections: the U.K.
Hadley Centre and the Canadian Centre for Climate Modelling and Analysis (CCCMA).
The former projections are comparable to those of the Intergovernmental Panel on
Climate Change (IPCC) 1995 mid- range scenarios, whereas the latter projections lie
toward the upper end of the IPCC range. The two models suggest that ocean waters in
this area could rise another 18 cm to 60 cm by mid-century, as the planet warms. By the
2080s, sea level could climb by 24 cm to nearly 110 cm, in some locations.
The area at risk to flooding is commonly defined in terms of the 100-year
flood (probability of occurring once in 100 years). At present, the 100-year flood height
in New York City and environs is slightly under 3 meters. As sea level rises, flood
levels produced by the 100-year storm could reach 3 to 3.8 meters by the 2050s, and
between 3.2 to 4.2 meters by the 2080s.
Even if storms (both hurricanes and nor’easters) do not grow in severity,
coastal flooding will become more frequent as sea levels rise. Thus, a smaller surge
would lead to coastal flood levels equivalent to that produced by a major storm today.
More importantly, the current 100-year flood return period would shorten dramatically.
Flood waters would periodically cover significant portions of lower Manhattan, Coney
Island, the Rockaways in nearby Queens, and entire neighborhoods on Staten Island. The
metropolitan transportation system could be seriously disrupted because most area rail
and tunnel entrance points, many transportation corridors, and portions of JFK,
LaGuardia, and Newark Airports lie at elevations of 3 m or less. A powerful nor’easter
with near hurricane-force winds struck the city on December 11-12, 1992, producing
some of the worst floods in 40 years that led to the almost complete shutdown of the
region’s transportation system as well as evacuation of many seaside communities.
Toward the end of the century, such storm floods would become a much more frequent
occurrence.
What can be done to stem the rising tide? The most direct step–curtailing
emissions of carbon dioxide and other greenhouse gases worldwide–faces considerable
political and economic challenges. Alternatively, dikes and seawalls can be built around
the airport runways and vulnerable low areas, peripheral highways can be elevated, and
beaches can be periodically replenished with sand. Legislation could require new
buildings to lie inland beyond a designated amount of sea level rise or erosion extent.
References: Gornitz, V., S. Couch, and E.K. Hartig 2000. Climate change and the coast:
Impacts in the New York City metropolitan region. EOS, 81 (19), S73. Gornitz, V., S.
Couch, and E.K. Hartig 2000. Impacts of sea level rise in the New York metropolitan
area. Global and Planetary Change, submitted.
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For further information contact:
Dr. Vivien Gornitz, Code 940
(212) 678-5566
http://www.giss.nasa.gov/research/intro/
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