Climate Change: Impact On Rising Seas

Millions Threatened by Rising Seas

Nearly 4 million Americans, encompassing a total area larger than the state of Maryland, could be underwater by the end of the century, suggest two new studies predicting the risk of flooding due to sea-level rise in the United States.

The news comes on the heels of reports that the Pacific nation of Kiribati is in negotiations to buy land on Fiji so Kiribati residents under threat of rising seas can move there.

As the planet warms, seas are expected to rise due to thermal expansion (water expands as it warms) and glacier melt. In their most recent report, the Intergovernmental Panel on Climate Change (IPCC), the international body charged with assessing climate change, estimates the seas will rise up to 6.6 feet (2 meters) by 2100; this number could be higher depending on the degree of ice melt at the poles and greenhouse gas emissions.

"The sea-level rise taking place right now is quickly making extreme coastal floods more common, increasing risk for millions of people where they live and work," Ben Strauss, co-author of both studies and researcher at Climate Central, said in a statement. "Sea-level rise makes every single coastal storm flood higher."

Strauss added, "With so many communities concentrated on U.S. coasts, the odds for major damage get bigger every year."

Both studies are detailed today (March 14, 2012) in the journal Environmental Research Letters.

In the first study, researchers from Climate Central and the University of Arizona created a model assuming a sea-level rise of 3.3 feet (1 m) or more by the end of the century. Results showed that in terms of area affected, regions surrounding the Gulf of Mexico may be the most vulnerable to flooding; in terms of population, Florida is the most vulnerable, closely followed by Louisiana, California, New York and New Jersey, they found.

The researchers also think Los Angeles is an area of concern due to its large population and previous research suggesting floods in southern California could reach rarely seen heights more quickly than in any other mainland U.S. area.

In the second study, researchers combined past data on the effects of heavy storms on water levels with estimates of future global sea-level rise. The past water level data came from 55 stations across the United States. The results suggest water levels that have previously been encountered only once a century could occur every decade or more, the researchers said.

The researchers liken the type of annual flooding that we may see to the infamous high water levels brought about in New York in 1992 by a strong nor'easter, which flooded the subway system.

The ocean has been rising slowly and relentlessly since the late 19th century, one of the hallmark indicators that the climate of the earth is changing. The average global rise has been about eight inches since 1880, but the local rise has been higher in some places where the land is also sinking, as in Louisiana and the Chesapeake Bay region.

The rise appears to have accelerated lately, to a rate of about a foot per century, and many scientists expect a further acceleration as the warming of the planet continues. One estimate that communities are starting to use for planning purposes suggests the ocean could rise a foot over the next 40 years, though that calculation is not universally accepted among climate scientists.

South Florida May be 'Indefensible'

Miami Beach About 3.7 million Americans live within a few feet of high tide and risk being hit by more frequent coastal flooding in coming decades because of the sea level rise caused by global warming, according to new research.

If the pace of the rise accelerates as much as expected, researchers found, coastal flooding at levels that were once exceedingly rare could become an every-few-years occurrence by the middle of this century.

By far the most vulnerable state is Florida, the new analysis found, with roughly half of the nation's at-risk population living near the coast on the porous, low-lying limestone shelf that constitutes much of that state. But Louisiana, California, New York and New Jersey are also particularly vulnerable, researchers found, and virtually the entire American coastline is at some degree of risk.

"Sea level rise is like an invisible tsunami, building force while we do almost nothing," said Benjamin H. Strauss, an author, with other scientists, of two new papers outlining the research. "We have a closing window of time to prevent the worst by preparing for higher seas."

The handful of climate researchers who question the scientific consensus about global warming do not deny that the ocean is rising. But they often assert that the rise is a result of natural climate variability, they dispute that the pace is likely to accelerate, and they say that society will be able to adjust to a continuing slow rise.

Experts say a few inches of sea level rise can translate to a large incursion by the ocean onto shallow coastlines. Sea level rise has already cost governments and private landowners billions of dollars as they have pumped sand onto eroding beaches and repaired the damage from storm surges.

Insurance companies got out of the business of writing flood insurance decades ago, so much of the risk from sea level rise is expected to fall on the financially troubled National Flood Insurance Program, set up by Congress, or on state insurance pools. Federal taxpayers also heavily subsidize coastal development when the government pays to rebuild infrastructure destroyed in storm surges and picks up much of the bill for private losses not covered by insurance.

For decades, coastal scientists have argued that these policies are foolhardy, and that the nation must begin planning an orderly retreat from large portions of its coasts, but few politicians have been willing to embrace that message or to warn the public of the rising risks.

Organizations like Mr. Ebell's, even as they express skepticism about climate science, have sided with the coastal researchers on one issue. They argue that Congress should stop subsidizing coastal development, regarding it as a waste of taxpayers' money regardless of what the ocean might do in the future.