July 3, 2012

Hatteras Island Real Estate:  Rising sea level


Over the past month, there have been an unusually large number of articles addressing a variety of issues related to the magnitude of sea level rise along our shores and the pace at which it is proceeding.

Some of this heightened interest was no doubt generated by a controversial bill recently introduced in the North Carolina legislature that would have restricted state and local agencies from using estimates by scientists of the anticipated sea level rise between now and the beginning of the next century in their policy and planning initiatives.

A second stimulus to the discussion resulted from a study released on June 24 by the U.S. Geological Survey (USGS) that reported that the ocean waters from Cape Hatteras to New England are rising at a rate three to four times faster than the global average.

With these events and studies in the news, it seemed like an appropriate time to dust off and update an article that I wrote about rising sea level almost 10 years ago.

Rising sea level has captured my interest for some time. It seems to be the most insidious element in the ongoing erosion saga – the “silent killer” so to speak.  A  book by Stanley Riggs and Dorothea Ames in 2003, “Drowning the North Carolina Coast: Sea-Level Rise and Estuarine Dynamics,” kindled my fascination with the subject, adding a heightened sense of urgency to the issue and providing a wealth of statistical data.

That book was followed up this year by another, “The Battle for North Carolina’s Coast,”  also written by Stan Riggs and three of his colleagues. Most who have read these books agree that it is hard to argue with the science presented about the coastal geology of the island, but the authors’ suggestions for dealing with the long-term effects of the natural forces have resulted in quite a bit of controversy.

Many scientists believe that the movement of sand along the shore in currents generated by wind and wave action has had the greatest impact on the island’s shoreline over the last 30 to 50 years.  Few of us would argue that the hurricanes and nor’easters that we experience often produce dramatic changes in our beaches.  

Sea level rise, on the other hand, is a long-term process contributing to erosion. It is so long-term in fact that we don’t directly observe its impact, or we tend to attribute its manifestations to other causes.  The issue is further masked because of the difficulty researchers have in gathering firm statistics on rising sea level.  Water levels change so slowly that it is not easy to accurately measure increases or decreases on an annual basis.
In the past, scientists had estimated that sea level along the North Carolina coast was rising at the rate of about one foot per century.  According the USGS report , data accumulated from tide gauges suggest that sea level north of Cape Hatteras may actually be rising at a faster pace that might equate to as much as a 39 inch rise by 2100.  Some observers hold the opinion that up to one half of long-term erosion may be due to changes in sea level.

As I understand the dynamics of the process, there are basically two ways for sea level to rise. You can increase the temperature of the water, which will cause a given volume of water to expand, or you can increase the total amount of water in a given area.  The technical term for increasing the water temperature is thermal expansion.  A USA Today article, reporting on conclusions reached by the International Panel on Climate Change (IPCC) in 1995, indicated “most of the expected sea level rise due to climate change will be from thermal expansion of the earth’s oceans due to greenhouse warming.”

Other factors were identified by the IPCC as primary contributors to changes in sea level.  Among these were the melting of glaciers as well as large icebergs breaking away from the main ice sheets in Greenland and Antarctica.  The effect of these phenomena would be an increase in the total amount of water in the oceans of the world.  Global warming, whatever the source, is an underlying theme in the overall analysis of sea level changes, and the rate of sea level rise is projected to increase.

After my article was originally published, one of my clients, a professor at UNC-Chapel Hill, observed that subsidence of the land can also affect sea level changes.  Subsidence is a decrease in the elevation of the land. Earlier this year, Dr. Riggs commented that subsidence was a negligible factor on Hatteras Island, but it could have a significant impact in other areas.

Up to this point, the story of rising sea level seems fairly straightforward.  It is my impression that most geologists would agree that sea level is on the rise.  However, once they delve deeper into the causes for sea level increasing or when they try to obtain information that is specific to a particular location, the seemingly hard statistics become less precise.  

This is where the debate starts to heat up.  What is the relative importance of each of the component factors?  How much of the global warming phenomenon is part of recurrent natural cycles, and how much is man-made?  Are natural cycles more or less significant than the actions caused by man?  Are the Greenland and Antarctic ice sheets shrinking or growing?  Definitive answers to many of these questions are hampered by the lack of reliable long-term data.  The apparent reality is that “… the scientific community has only a moderate understanding of the linkages and controls between global warming and changing magnitude and rate of sea level response…”

After we get past the scientific investigations and debates, are there any tangible indicators of rising sea level that we can see and touch here on the Outer Banks?  In fact, there are quite a few!  One of the clearest examples is the beach in front of the former location of the Cape Hatteras Lighthouse.  According to a National Park Service publication, when the lighthouse was constructed in 1870, the beach was located about 1,300 feet east of its present position.  Another source estimates the erosion at closer to 3,000 ft.  

Have you ever picked up oyster shells while you were beachcombing?  Oysters grow in sounds and bays.  The shells that we find today at the edge of the ocean were at one time growing on the bottom of an ancient sound.  The tree stumps that we see on parts of the beach on Hatteras and Ocracoke islands tell us that forests once stood where the sea now breaks.  Clearly, rising sea level is not the sole cause of the retreating shoreline, but it is certainly a factor in the overall equation.

Areas along the shores of the sound offer similar observations.  Archeologists tell us that parts of the earliest European settlements on Roanoke Island are now underwater, and there is evidence that a portion of the ancient Croatan Indian village near Buxton is also submerged.  Heading toward Greenville along routes 64 and 264, it is hard not to note that the road is higher than the surrounding swampy land.  The dead stumps throughout the area are the remnants of drowned trees and saltwater intrusion.  One of the more remarkable statistics presented by Dr. Riggs and his co-author was that the range of shoreline erosion at the north end of Roanoke Island has been from 1 foot per year to as much as 25 feet per year with an average of 6 feet per year.  Again, a rise in sea level is not the only culprit, but it is difficult to ignore as a contributing factor.

So, where does all of this leave us when we search for answers about the future impact of sea level changes on Hatteras Island?  In my opinion, the best that we can do is to gain some directional understanding from the studies, reports, and public discussions.  

My personal summary of the issues might go something like this.  Sea level is rising, and it will continue to rise for the foreseeable future.  It is probably rising at a faster pace than scientists had previously estimated.  Whether man-made or cyclical, global warming will be a major contributor to sea level rise.  

Rising sea level will most assuredly affect us on Hatteras Island, even though we may not recognize that changing sea level is causing some of our erosion problems.  The effects of a rise in sea level will probably be felt the most in those areas of the island where the slope of the beach has historically been the flattest.  We also need to keep a close eye on shoreline changes along the soundside of the island.

 In the not too distant future, we will almost certainly have a much clearer and more accurate understanding of changes in sea level because of advances in the sophistication of data gathering technology.  The information contained in “Drowning the North Carolina Coast”  and “The Battle for North Carolina’s Coast,”  as well as the recent USGS report are examples of this progress.

The issues that we continually face as we seek solutions for the future of Highway 12 and the areas of repeated ocean overwash should not come as a surprise to any of us.  I think it was Orrin Pilkey who observed in one of his books, “Sand was meant to move.”  When you combine the inclination of sand to move with the long term natural forces that influence our island, it is reasonable to expect to see changes in the configuration of the island over time. How we will respond to these changes is the real question.

One of the challenges, as I see it, is that the focus of our dialogues may be too short term.  To illustrate this point, all we have to do is to remember that when the first Europeans arrived over 400 years ago, Hatteras Island began in the vicinity of what is today the north end of Buxton and encompassed the northern end of present day Ocracoke Island.  Oregon and Hatteras inlets did not exist, and there was an active inlet where the road has been rebuilt several times between Avon and Buxton.

On a barrier island, change is the only constant. Those of us who live here now and those who lived here before the first Europeans arrived have had to deal with the natural forces that continuously reshape the island. Adaptability is the characteristic that has assured survival up to this point, and I believe that it will be adaptability and creativity that will assure that the beauty and pleasures of Hatteras Island will be here for the enjoyment of many generations to come.


In conjunction with this article, you may enjoy the following Island Free Press resources:

Seas Rising Faster Along the Northern Outer Banks - http://tinyurl.com/6uabyqa

Sea-Level Rise: The onrushing train

Senate committee supports bill that restricts sea-level rise definition http://tinyurl.com/6s4uu8k

Sea-level rise debate may move to Raleigh

State sea-level rise policy won't affect insurance rates

(Tom Hranicka is an associate broker with Outer Beaches Realty. Questions, comments, or suggestions for future articles may be sent to Tom Hranicka at P.O. Box 237, Avon, NC  27915, or e-mail to [email protected] )
Copyright 2012 Tom & Louise Hranicka.  All rights reserved.

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