Friday, June 15, 2007

Rising Sea Level Redefines N.C.Coast

The following was printed in today's News and Observer, written by Wade Rawlins. The link is:

By the way..this is very very long!!

Rising sea level redefines N.C. coast

If climate predictions hold, the transformation of islands and rivers will speed up
In North Carolina, global warming isn't a future worry. It's already lapping ashore.

Nags Head Mayor Renee Cahoon sees all the proof of climate change she needs at the end of Old Oregon Inlet Road. The street once led to rows of oceanfront houses. Now it ends suddenly in bulldozed piles of sand.

Some beach erosion occurs naturally, and development near the ocean tends to make it worse. But some scientists think erosion has grown more pronounced in recent years as the sea level has risen and storms increased. On some days, stretches of Nags Head have no dry beach, and visitors have to sit under the front-row houses at high tide. The resort that once thrived by the sea is being swallowed by it.

"We are losing the town," Cahoon said. "As sea level rises, our tax base goes away."
Other, more subtle changes are under way along the coast, not just on the fragile barrier islands. As salt water pushes farther upriver, some rivers are widening into estuaries, tidal bodies of water where fresh and salt water mix. Freshwater swamps are changing to salt marsh.

"The shore is the line of conflict where this crisis is taking place," said geologist Stan Riggs, designated a distinguished research professor at East Carolina University. "We can't think we're going to hold the line."

Scientists predict that the buildup of carbon dioxide gas in the atmosphere will lead to higher global temperatures. That warming will cause seas to rise faster and increase erosion driven by storms.

Changes are already occurring. The world's oceans rose about 6 inches to 8 inches during the 20th century. In North Carolina, the ocean has grown higher by about 8 inches in the past century, because much of the coast is also slowly sinking as the land settles.

A panel of international scientists projects the seas will rise 7 to 30 inches in the next century unless there is a substantial reduction in the emission of man-made greenhouse gases such as carbon dioxide. Those gases spew from our cars, power plants and appliances, accumulating in the atmosphere and trapping heat.

Hundreds of scientists from 40 countries this year proclaimed that climate change is "unequivocal." Global air and water temperatures are inching up, causing seas to warm and expand, and polar ice to melt -- triggering higher sea levels.

There's still debate over how much of the observed change in temperature is due to man-made carbon dioxide and how much comes from the natural cycles of weather. But there's little argument that North Carolina's water, air, food and land are being altered. And more rapid change is predicted.

Swamps turn salty
Gray trunks of dead cypress trees line the shore of the Northeast Cape Fear River a few miles upstream from downtown Wilmington. The trees have been essentially drowned by salt water. Tupelo gum, red maples and other tree species have already disappeared, unable to tolerate the chemical reactions of salt water in soil.

Rising sea levels are pushing high ocean tides of salt water farther up the river.

The soil, exposed to salt, gradually disintegrates, leaving tangles of gnarled cypress roots clinging to air where a riverbank once stood. The disintegrating soil releases carbon dioxide into the atmosphere, adding to global warming. As the trees die, a freshwater swamp changes into a salt marsh.

As the bank crumbles, the river is broadening and transforming into an estuary such as the Pamlico Sound or Chesapeake Bay. The Cape Fear River basin has 200,000 acres of timber that will eventually turn into marsh, said Courtney Hackney, a marine biologist at UNC-Wilmington.

The enlarging estuaries will create more habitat for saltwater fish, crabs and shrimp. But the freshwater swamps will disappear, along with the trees that provide homes for songbirds that thrive there. Ultimately, some landowners will lose their land.

"This swamp was alive when I first arrived and started working on the river in the 1980s," Hackney said as he accompanied a group of students upriver to monitor water levels in swamps. "This has all happened in 30 years, basically. This will all be marsh in five to 10 years."

The Northeast Cape Fear River, which flows into the Cape Fear at Wilmington, is showing effects of rising seawater. The fresh water flowing downriver isn't enough to keep the salt water from intruding upriver.

During the drought of 2001, the researchers detected low levels of salt water more than 16 miles up the Northeast Cape Fear. That's 45 to 50 miles from the ocean.
"We're going through a transition that is far beyond the history of humans on the continent," Hackney said. "There hasn't been salinity where we're seeing it on the Coastal Plain in 50,000 or 100,000 years."

Clues from the past
About 200 miles north of Wilmington, the Great Dismal Swamp is giving researchers from East Carolina University a look into the past, which may offer clues to the future. It's a layer cake of Earth's history.

Vast areas of Eastern North Carolina were ancient ocean beds at a time when sea levels were 20 feet higher. Pete Parham, a graduate student in geology, and Dave Mallinson, an assistant professor, have been drilling east of a low ridge thought to mark an ancient barrier island shoreline that existed between 125,000 and 80,000 years ago.
The line of sand is called the Suffolk scarp. It runs north-south near the present towns of Edenton, Plymouth and Bath.

Mallinson said that about 130,000 years ago, the shoreline was about where it is today. Then, polar regions grew significantly warmer for an extended period. Sea level rose 15 to 20 feet. All or parts of a dozen counties of present-day Eastern North Carolina were submerged, making areas of Gates and Washington counties beachfront.

"Some evidence suggests it rose fairly rapidly up to the Suffolk shoreline," said Mallinson, a geologist at East Carolina University. "That is what we think may be beginning to happen today."

Two factors in rise
Two things are contributing to rising seas. Rising temperatures cause ocean waters to warm and expand, like water heated in a teakettle. Rising temperatures near the poles cause massive ice sheets to melt, adding to the volume of water. Scientists are particularly worried about ice melts in Greenland and the Canadian Arctic, where giant shelves of ice, some the size of Manhattan, have begun crumbling.

"As the Greenland ice sheet melts, that is where the shoreline is going to go," Mallinson said, referring to the ancient shoreline. "Sometime in the next few hundred to 1,000 years, maybe less."

Scientists can observe ancient climate change by studying the layers of sediment. What they don't understand is what triggered the big changes: Did carbon dioxide levels rise in previous eons as a result of warmer temperatures, or did carbon dioxide levels drive temperature increases?

The ECU scientists try to tease answers from the mud, sand, shell and sediment they pull from the depths of the swamp. The drill, mounted in a pickup truck bed, sounds like a jackhammer as it drives the hollow, 2-inch-thick steel tubes into gray mud to collect the samples of sediment. Each 4-foot cylinder contains a snapshot of the time when the sediment was deposited.

"It's important to understand the past sea level cycles so we can better understand the one we're in now," Parham said. "Sea level is rising. We'd like to get an idea what is going to happen. We can do that by looking in the past when sea level was higher than it is today."

Vulnerable Outer Banks

Nowhere are rising sea levels more pressing than the Outer Banks, which are among the nation's most vulnerable land forms. The low-lying barrier islands stretch from Currituck County to Carteret County, and for centuries have defined North Carolina's coastal culture. The most dire scenarios predict collapse of the Outer Banks within a century.

It's a process that has historic precedent. Scientists think the Outer Banks have collapsed and re-formed more than once -- they held far more inlets at the time Columbus landed in the Americas.

The natural tendency of undeveloped barrier islands is to move toward the mainland in response to rising seas. Sand on the oceanfront side gets pushed by waves and blown by wind onto the backside in a gradual, yet massive rolling motion. That pattern has been disrupted on parts of the Outer Banks by artificial dunes, which stop waves from washing across the island and depositing sand on the backside. So the islands grow thinner and thinner.

With global warming, they may grow thinner still. A new study by Laura Moore, a geologist at Oberlin College in Ohio, said sea level rise is the most important factor determining movement of the barrier islands over the next century.

Moore and her colleagues at the U.S. Geological Survey used a computer model to simulate the movement of the Outer Banks over the past 8,500 years. They used the model to predict the Outer Banks' response to various amounts of sea level rise over the next century, as presented by the Intergovernmental Panel on Climate Change, the leading source of scientific consensus on climate change.

Moore's study suggests that by the next century, the barrier islands might move toward the mainland up to 2.5 times faster than current long-term erosion rates. That's based on projected sea level rise of 19 to 34 inches. Houses would be washed into the sea more quickly, and highways overtaken by sand, but Moore said the Outer Banks would likely remain intact.

But other scientists, including ECU's Riggs, have said that the international panel's projections are too conservative and that warming might cause the Greenland ice sheet and West Antarctic ice sheet to melt more quickly, possibly causing much higher sea levels by 2100.

Riggs said the rate of sea level rise in northeastern North Carolina around Nags Head and Kitty Hawk is already approaching the climate change panel's midrange predictions for 100 years from now.

A state panel is studying the potential impact of global warming but has yet to make substantial recommendations. Meanwhile, the Coastal Resources Commission, which sets rules for shoreline development, is re-evaluating how close to the shore developers may build houses. And the state spends hundreds of thousands of dollars maintaining the highway that cuts through the Outer Banks.

Higher sea levels turbocharge erosion -- especially during storms -- putting more houses in peril and increasing the costs of maintaining the beaches. Riggs said about 22 miles of the Outer Banks are starting to collapse right now, including narrow, low-lying stretches of Hatteras Island, Ocracoke, Pea Island and Rodanthe. He said only constant bulldozing has prevented the ocean from washing over and cutting through the islands.

Anthony Roper, a state transportation division engineer who oversees the area, doesn't use the term collapse. But transportation officials battle the ocean nearly every year to keep N.C. 12 open. Roper said a half-dozen hot spots on the thinning islands require frequent repairs and rebuilding of dunes to keep them passable.

At Rodanthe, the edge of the highway is about 50 feet from the ocean at high tide. The surf washed over the highway during an extended nor'easter at Thanksgiving, costing more than $1 million to repair.

A little farther north, highway planners propose to replace a stretch of N.C. 12 through Pea Island National Wildlife Refuge by building an elevated highway as the island erodes. In the meantime, the planners project spending $23.7 million to $36.3 million on more sand through 2015 to protect the threatened road.

"The right storm event, if we don't do anything different, we'll have challenges maintaining the road," Roper said.

Riggs holds up a map depicting the disintegration of the Outer Banks, leaving only higher sections of the islands.

"If we had a Katrina-like storm," he said, "it could look like that this summer. This is what nobody in North Carolina is prepared for."

This just saddens me. I LOVE the outer banks..and to think that Okracoke could just be gone one day bothers me.