Global warming fuels 'high-tide' floods — and it's going to get worse

Doyle Rice | USA TODAY

Show Caption Hide Caption Nor'easter drops heavy rain, snow on the East Coast A fierce nor'easter has downed trees and power lines, causing widespread problems across the Northeast. Parts of Massachusetts saw heavy flooding, while Buffalo, N.Y. was buried in snow. (March 2)

Snow may get the most headlines from nor'easters, but it's the relentless onslaught of waves and water along the coast that can cause the most destruction.

Thanks partly to global warming, it doesn't even take a storm to inundate the coast with ruinous floodwaters.

"Nuisance" or "sunny day" high-tide flooding is becoming more commonplace across the USA, and a federal report released this week warns that such flooding will worsen in the decades to come.

By the end of the century, such flooding could be a weekly, or even daily, event in some vulnerable locations of the country, such as Miami, Charleston, S.C., and Norfolk, Va.

"The risk of coastal flooding has been steadily increasing and will continue to in the coming decades," said oceanographer William Sweet, the report's lead author. At many locations, "today’s storm flood will become tomorrow’s high tide sometime this century," he said.

The report prepared by the National Oceanic and Atmospheric Administration found that rising seas are the cause: "Due to rising relative sea level, more and more cities are becoming increasingly exposed and ever more vulnerable to high-tide flooding, which is rapidly increasing in frequency, depth and extent along many U.S. coastlines," the report said.

Erika Spanger-Siegfried, a senior climate analyst from the Union of Concerned Scientists, told CNN that "with sunny day flooding, we see a high tide on steroids."

"It can reach into our communities and leave us stranded in our cars, stuck at home, sloshing through water, unable to get to school and work ... (It's) not a catastrophic flood, but it can disrupt our ability to go about our normal lives," Spanger-Siefried said.

The NOAA report was published to better inform coastal citizens of the risks they face and to assist in coastal planning, Sweet said.

Sea level has risen nearly 8 inches worldwide since 1880, but unlike water in a bathtub, it hasn't risen evenly. In the past 100 years, it has climbed about a foot or more in some U.S. cities because of ocean currents and land naturally settling — 11 inches in New York and Boston, 12 in Charleston, S.C., 16 in Atlantic City, 18 in Norfolk, Va., and 25 in Galveston, Texas, according to NOAA.

As the Earth's temperature warms, so do the seas. Heat-trapping greenhouse gases such as carbon dioxide and methane cause more land ice (glaciers and ice sheets) to melt and water to expand. Warmer water takes up more room than cooler water.