Rising Seas: A View from New York City
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? (Figure 1). 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.
We estimate future sea levels 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 (Figure 1).
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. Such a flood could cover most of the area outlined in blue
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. By the 2080s, the likelihood of a flood engulfing the area in blue (Figure 2) would be once in 50 years, given present rates of sea level rise, and as often as once every 4 years, in the worst-case scenario.
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 less 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.
Gornitz, V., S. Couch, and E.K. Hartig 2000. Climate change and the coast: Impacts in the New York City metropolitan region. Eos 81, S73.
Gornitz, V., S. Couch, and E.K. Hartig 2001. Impacts of sea level rise in the New York metropolitan area. Global Planet. Change 32, 61-88.
Please address all inquiries about this research to Dr. Vivien Gornitz.