Sea level already becoming an urban factor

Inside Climate News- To get a sense of how much it will cost the nation to save itself from rising seas over the next 50 years, consider Norfolk, Virginia.

In November, the Army Corps released a proposal for protecting the city from coastal flooding that would cost $1.8 billion. Some experts consider the estimate low. And it doesn't include the Navy's largest base, which lies within city limits and likely needs at least another $1 billion in construction.

Then consider the costs to protect Boston, New York, Baltimore, Miami, Tampa, New Orleans, Houston and the more than 3,000 miles of coastline in between.

Globally, seas have risen about 7 to 8 inches on average since 1900, with about 3 inches of that coming since 1993. They're very likely to rise at least 0.5-1.2 feet by 2050 and 1-4.3 feet by 2100, and a rise of more than 8 feet by century's end is possible, according to a U.S. climate science report released this year. Because of currents and geology, relative sea level rise is likely to be higher than average in the U.S. Northeast and western Gulf Coast.

By the time the waters rise 14 inches, what's now a once-in-five-years coastal flood will come five times a year, a recent government study determined. By 2060, the number of coastal communities facing chronic flooding from rising seas could double to about 180, even if we rapidly cut emissions, according to a study by the Union of Concerned Scientists. If we don't slash emissions, that number could be 360.