The research is the first analysis of vulnerability to sea level rise that includes every U.S. coastal city in the lower 48 with a population of 50,000 or more.
Cities along the Gulf of Mexico and southern Atlantic coasts such as Miami, New Orleans, Tampa and Virginia Beach will be particularly hard hit, the researchers discovered.
"Our work should help people plan with more certainty and to make decisions about what level of sea-level rise, and by implication, what level of global warming is acceptable to their communities and neighbors," said co-author Jonathan Overpeck, a professor of geosciences and of atmospheric sciences and co-director of University of Arizona's Institute of the Environment.
The low-lying city of Tampa, Florida is predicted to experience sea level rise. (Photo by JS Design)
In total, 20 U.S. municipalities with populations greater than 300,000 and 160 municipalities with populations between 50,000 and 300,000 have land area with elevations at or below six meters (19.6 feet) and connectivity to the sea.
Overpeck and his colleagues examined how much land area from the 180 municipalities could be affected by one to six meters of sea level rise.
The latest scientific projections indicate that by 2100, sea levels will rise about one meter (39 inches). At the current rate of global warming, sea levels are projected to continue rising after 2100 by as much as one meter per century.
"According to the most recent sea level rise science, that's where we're heading," said lead researcher Jeremy Weiss, a senior research specialist in the University of Arizona's Department of Geosciences. "Impacts from sea-level rise could be erosion, temporary flooding and permanent inundation."
"With the current rate of greenhouse gas emissions, the projections are that the global average temperature will be eight degrees Fahrenheit warmer than present by 2100," said Weiss.
"That amount of warming will likely lock us into at least four to six meters of sea-level rise in subsequent centuries," Weiss predicted, "because parts of the Greenland and Antarctic ice sheets will slowly melt away like a block of ice on the sidewalk in the summertime."
At three meters (9.8 feet), on average more than 20 percent of land in those cities could be affected. Nine large cities, including Boston and New York, would have more than 10 percent of their current land area threatened.
By six meters, about one-third of the land area in U.S. coastal cities could be affected, the researchers determined.
The coastal municipalities the team identified had 40.5 million people living in them, according to the 2000 U.S. Census. Twenty of those cities had more than 300,000 inhabitants.
Weiss, Overpeck and Ben Strauss of Climate Central in Princeton, New Jersey, will publish their paper, "Implications of Recent Sea Level Rise Science for Low-Elevation Areas in Coastal Cities of the Conterminous U.S.A.," in the journal "Climatic Change Letters," online this week.
Their research confirms earlier studies of sea level rise impacts. Conservative projections of sea level rise by the end of the century have predicted seven to 23 inches, and some projections predict a rise of more than 4.5 feet by 2100.
Weiss and Overpeck point to recently published work estimating that global sea level rise approaching or exceeding one meter by 2100 is plausible, thus significantly updating projections by the Fourth Assessment of the Intergovernmental Panel on Climate Change.
Some states are already preparing for rising sea levels. On December 31, 2010, the New York State Sea Level Rise Task Force, created by the state legislature in 2007, presented its report.
"Sea level rise and coastal flooding from storm surge are already affecting and will increasingly affect New York's entire ocean and estuarine coastline from Montauk Point to the Battery and up the Hudson River to the federal dam at Troy," the Task Force stated.
Low-lying New York City is vulnerable to sea level rise. (Photo by Roman Lipovskiy)
More than 62 percent of New York's population lives in marine coastal counties, and these areas have tremendous economic value in terms of commerce and natural benefits such as habitat, water-quality improvement, flood control, and storm protection, the report says.
"The likelihood that powerful storms will hit New York State's coastline is very high, as is the associated threat to human life and coastal infrastructure. This vulnerability will increase in area and magnitude over time," the Task Force warned.
Sea level rise affecting the Lower Hudson Valley and Long Island, including New York City, is projected to be two to five inches by the 2020s and 12 to 23 inches by the end of this century, according to the Task Force. "However," its report warned, "rapid melt of land-based ice could double these projections in the next few decades, with a potential rise of up to 55 inches by the end of the century."
Public and private infrastructure dominates large sections of New York's coastline and the coastlines of many other coastal cities studied by Overpeck and Weiss.
This infrastructure includes power plants, sewage and drinking-water treatment plants and pump stations, landfills, waste transfer stations, major road and rail transportation networks, air and sea ports, and a host of industrial facilities.
Beneath the streets of New York City, and other coastal cities, elaborate systems of public utilities are vulnerable to increased flooding from the intrusion of surface water as well as from rising groundwater levels.
The New York State Sea Level Rise Task Force advises the legislature to begin "proactive adaptation planning" before sea level rise and related coastal hazards worsen current flooding problems that much of New York State's coastal infrastructure already faces and create new problems as well.
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