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Hampton Roads in southeastern Virginia is unusually vulnerable. It is flat, and its land is sinking. It has nearly 2 million residents. It is home to popular beaches, waterfront homes, military bases, a huge tourism industry and ecologically valuable marshes.

"Hampton Roads is one of the most vulnerable regions in the United States to sea-level rise, in terms of population and assets at risk," said Eric J. Walberg, a former staff member for the Hampton Roads Planning District Commission.

Rising sea levels around the world are attributed to warming. When water warms, it expands. Melting polar ice sheets also raise the waters. In Virginia, sea levels are rising faster than the global average because the land is sinking

During the last ice age thousands of years ago, the weight of glaciers pushed down land in what is now the northern U.S. When those glaciers receded, that northern land began to rise, and land here started sinking, as if Virginia were on the end of a see-saw after the other rider got off. Throughout most of the 20th century, the sea level in southeastern Virginia rose about twelve-hundredths of an inch a year -- or 12 inches per century. But over the past two decades or so, the rate appears to have doubled in places. About half of that increase seems to be due to the sinking of land, and half to global warming, said Carl Hershner, a professor at the Virginia Institute of Marine Science. "And the forecast -- this is the scary part -- is for that acceleration to rise," Hershner said. Scientists say the future increases will be caused almost entirely by climate change. "We will still be sinking," Hershner said, "but that will be a smaller and smaller fraction of the change we experience."

Many of the piers at the Norfolk Naval Station were built around World War II. During storms or even higher-than-normal tides in recent years, the water began to rise so high that it flooded low-lying areas of the base and covered utility lines, including high-voltage electrical cables, suspended beneath the old piers. That meant frequent losses of power and other services to the base's ships. "Sea-level rise was having a negative impact on the readiness of the combat forces at the base," said Joe Bouchard, the base's commander from 2000 to 2003.

The Navy was already planning a multimillion-dollar project to replace the aging piers at Norfolk, the world's largest naval base. To cope with the rising waters, Navy engineers designed double-deck piers with the utility lines suspended from the main, upper deck, about 20 feet above sea level.

Cmdr. Wendy L. Snyder, a Defense Department spokeswoman, acknowledged that flooding occurs at the Norfolk and Langley bases. The department is concerned and is studying the problem, she said. "We are going to assess the impacts of climate change for all of our installations." As for possible base closings in Hampton Roads, Snyder said she did not want to speculate.

A powerful storm hit Virginia's coast in 1933. But the less-powerful Hurricane Isabel in 2003 -- which became a tropical storm about the time it entered Virginia -- caused similar flooding because the sea level by then had risen 9 to 10 inches. Isabel gained extra destructive power by sending its storm surge inland on higher waters, Hershner said. Isabel caused hundreds of millions of dollars in damage. On top of all that, scientists predict global warming will cause more-powerful storms in coming decades. And in Hampton Roads, more and more people are building near the shore, putting themselves and their property at risk.

Low-lying parts of Hampton Roads flood now from fairly routine storms and tides, said Skip Stiles, director of Wetlands Watch, a Norfolk environmental group. "Anywhere you go, people have stories" about how the water comes up higher than it used to.

There is agreement on one issue: excess greenhouse gases in the atmosphere will increase the intensity of storms (in general) and especially rainfall, since warmer conditions allow more water vapor to be sucked from the air. The higher risk of flooding is especially problematic for coastal areas because of storm surge. Researchers analyzing streamflows in large basins and GHG trends conclude that so-called 100-year floods likely will become more frequent.