Editor’s note: In the past week or so, Ocracoke has experienced record-setting rain, with more than 12 inches. More is expected throughout the week. The many puddles and flooded roads in the village are not the result of sea level rise. Nevertheless, rising seas are a concern for the island. This story was published in the May print issue of the Ocracoke Observer, and is still timely.
By David Mickey
We’re at a tipping point regarding sea level rise and science shows that rising carbon dioxide emissions worldwide are to blame.
“(Sea level) rise has never changed at the rate it’s changing now,” said Dr. Reide Corbett, an oceanographer, professor and program head of coastal processes at the UNC Coastal Studies Institute, Wanchese, in a talk April 16 in the Community Center, hosted by the Ocracoke Civic and Business Association (OCBA) and the Ocracoke Waterways Commission.
How soon the level goes beyond the potential point of no return depends on public response.
“The Intergovernmental Panel on Climate Change says if we curb CO2 emissions, the rate of sea level rise levels out by 2050,” he said. “Beyond that there’s a huge difference in the scenarios.”
By the year 2100 the increase could be dramatic–36 inches of sea level rise if CO2 emissions continue to increase at today’s rate and a minimum 12 inches if emissions are reduced.
“Curbing CO2 emissions today will have an impact 60 to 70 years down the road,” he said.
Corbett, who studies the science of sea level rise, said the global sea level has never been constant.
“There’s not one single rate (of change) we can look forward to,” he said.
But the science is clear: Sea level rise is occurring and will continue well into the future. Coastal communities like Ocracoke face numerous challenges that require adaptive planning.
Corbett encouraged local involvement in making the “tough decisions that will ultimately need to be made.”
He made his case by explaining what is known about North Carolina sea levels in the geologic past.
The balance between water in the oceans, frozen water in glaciers, ground, lake and river water changes through time. During an ice age water is removed from the ocean and accumulates in glaciers: Ice sheets form and sea levels fall.
Sea level worldwide was approximately 350 feet lower 20,000 years ago than it is today.
But 120,000 years ago, during the Earth’s last interglacial periods between ice ages, sea level was much higher (20 to 25 feet) and the North Carolina shoreline, known today as the Suffolk Scarp, reached as far inland as Edenton and Bath.
All the glaciers are currently retreating, adding water to the ocean, he said. Moreover, overall ocean temperature is warmer now than in 1900, leading to higher sea level due to water expansion.
“We have warmer temperatures over the whole planet,” he said. “The earth is one degree Celsius warmer today than it was 100 years ago.”
Rising and falling sea levels correspond to changing levels of greenhouse gases in the atmosphere and corresponding temperature change, he said.
As fossil fuels are burned and greenhouse gas levels go up, global temperatures rise, glaciers melt and the volume of water in the oceans grows.
Corbett recalled the 2010 Coastal Resources Commission panel that projected a sea level rise of 39 inches by the year 2100. This report led to legislation prohibiting the use of any projection greater than the historical rate of increase, or about eight inches by 2100.
Accused of making sea level rise illegal in North Carolina, the legislature in 2012 called for a new study but limited future projections to 30 years.
The revised report was released in 2015 and this time the science panel gave three projections: “Tide gauge,” (using rates of the recent past and projecting forward), “business as usual” (no reduction in greenhouse gas emissions) and “sharply reduced CO2 emissions.”
Recent research into the frequency of coastal flooding has shown that, regardless of the rate of rise, as the mean sea level increases, North Carolinians should expect more frequent flooding of low lying areas, Corbett said.
Beach erosion in some areas is a more immediate threat. Island narrowing–shoreline erosion of both the oceanfront dunes and the sound side marshes–is aggravated by rising sea levels and more frequent storms.
For example, Hurricane Isabel in 2003 was a critical event as this hurricane tore through the Outer Banks, narrowing parts of Ocracoke Island by up to 35 percent.
“Pre-Isabel, Ocracoke had a strong dune line,” he said. “Since then, the dunes have deflated.”
Erosion continues, and Corbett noted the dramatic erosion on the north end of Ocracoke. The North Carolina Department of Transportation has designated the five miles between the Pony Pens and the north end as the “Ocracoke hot spot.”
Another concern for Ocracoke can be seen on the Hatteras side of Hatteras Inlet where shoreline erosion threatens the power line. Rudy Austin, OCBA president, said Tideland EMC is evaluating the precautionary option of burying its line beyond the Graveyard of the Atlantic Museum, an expensive proposition.
Corbett listed three management-type responses to sea level rise: protection, accommodation and retreat. Beach nourishment is a widely used approach that provides short-term protection at a very high and recurring cost.
Accommodation “implies the continued use of the at-risk land, but not preventing the change (e.g., inundation or erosion).”
For example, NCDOT is planning for a new “jug handle” bridge in Rodanthe by relocating N.C. 12 over the sound and bypassing the over wash hot spot near Mirlo Beach.
Retreat (not protecting or accommodating for the rising sea) involves moving structures back from the water as was done with the Cape Hatteras Lighthouse in 1999.