Oct. 01, 2005

N.C. coastal future sits in jeopardy

BRUCE HENDERSON
Charlotte Observer Staff Writer

Rising seas and sinking land make the N.C. coast ever more vulnerable to a turbulent era of hurricanes and climate change, new research shows.

A map of the N.C. coastline for the first time combines creeping sea level and a coastal plain that's been sinking since the last ice age. The worst-case scenario: more than 2,000 square miles of coast, nearly four times the size of Mecklenburg County, under water by 2100.

Rising water could reshape the nation's second-largest estuary, threatening storm-buffering wetlands, speeding erosion and flooding, turning brackish Pamlico Sound to salty Pamlico Bay.

A Category 4 hurricane like Katrina would fast-forward those changes, experts say, by punching new holes in the protective shield of the Outer Banks.

"The N.C. coast is not a bathtub that will flood gently. This whole process is driven by high-energy coastal storms," said East Carolina University geologist Stan Riggs, who has studied the coast for 40 years.

Rising water and erosion may already swallow some 1,250 acres of shoreline and wetlands along the northeastern N.C. sounds each year, he has estimated.

If sea-level rise and storm intensity continue at their current levels, Riggs calculates, chunks of Hatteras and Ocracoke islands could be lost in a decade or two. A couple of Category 4 or 5 hurricanes could do it sooner.

Hurricane strikes on the Carolinas have increased since 1995, as part of a stormy North Atlantic cycle that could last another 20 years. It's unrelated to climate change, experts say.

But warming seas have also apparently driven up the intensity of hurricanes in recent years, controversial new studies say.

North Carolina ranks third on the Atlantic and Gulf coasts, behind Louisiana and Florida, in the area of low-lying land vulnerable to rising seas. Most of that lies on the northern coast, above Cape Lookout, where the easily eroded shoreline lies barely above sea level.

Global sea level is most likely to rise about 19 inches this century, an international panel on climate change estimates, but it could go higher. How much depends on where it's measured.

The current rate, rising about one foot a century on the N.C. coast, appears to have nearly doubled in the past dozen years, NASA said in a recent study.

"The coast is always going to be there," said marine geologist Jeff Warren of the N.C. Division of Coastal Management. "It's just a question of where it will be."

Sinking dates back centuries

Duke University research scientist Ben Poulter recently mapped the N.C. coast to show the effect of predicted sea-level rise. But he added a new twist: the sinking coastal plain.That's a legacy of the last ice age, which ended about 10,000 years ago.

As glaciers sank into the Earth's crust, the land around them rose, the way water rises when somebody sits in a bathtub. When the ice began to melt, the bordering land slowly began to subside.

That land is still sinking at nearly 8 inches a century.

By 2100, Poulter estimated, from 904 to 2,055 square miles -- including parts of the Outer Banks south of Manteo and the large peninsula between Albemarle and Pamlico sounds -- will be vulnerable to rising water.

What actually happens will also depend on other factors that Poulter didn't try to predict. Marshes and islands, for example, tend to rise as water levels do. Besides, he said, "Everything changes if there are several (barrier island) breaches from one storm."

Hurricane-widened inlets, or parts of the Outer Banks eroding as waters rise, would profoundly change life in the protected sounds.

Rich in wildlife and a nursery to most Atlantic seafood species, the vast Albemarle and Pamlico sounds are "ground zero for ecological changes" from sea-level rise, said Doug Rader, a marine ecologist for the advocacy group Environmental Defense.

When Hurricane Isabel drilled a 1,700-foot-wide inlet through Hatteras Island two years ago, the Pamlico's waters quickly grew saltier. Tourists don't care about salinity, but it's crucial to crabs, fish and oysters.

Along the sounds' 4,000 miles of shoreline, wetlands could shrink as the water rises. Bottom-rooted plants that hide young fish may die as they get less sunlight. Oysters might not survive saltier waters.

The National Oceanic and Atmospheric Administration last month launched a three-year, $3 million study of the ecological impacts of the rising sea on Pamlico and Bogue sounds.

The fate of the barrier islands is critical to the sounds, said NOAA program director Carol Auer. "If you lose them," she said, "you're in big trouble."

Storms would speed process

Stormier seas from the changing climate could resculpt the N.C. coastline even faster than rising sea level, said Duke researcher Brad Murray, who studies how coastlines evolve.

Over thousands of years, he said, the coast has adjusted itself to the angle of the waves that lap at it. Change those wave patterns -- bigger waves coming from new directions -- and the coastline will quickly reshape itself.

That means heavier erosion in many places, and widening beaches in others. Even now, one storm can wash away 20 feet or more of beach.

After a three-decade lull, three hurricanes slammed the N.C. coast in 1996. Five more, counting Ophelia last month, have followed since.

A Category 4 hurricane like Katrina has a 1 percent chance of hitting the N.C. coast in any year. Only one such hurricane reeled ashore in the past century: Hazel, in 1954.

Our coast stood about a half-foot higher then, compared to now. Hazel wiped it clean.
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Bruce Henderson: (704) 358-5051; bhenderson@charlotteobserver.com.