North Carolina scientists mapping future sea-level rise will have their last public meeting Monday before the group issues its much-anticipated projections this month to prepare coastal residents for increased flooding and more violent storm surges.
The science panel’s report will be the first of its kind in the nation. Rather than providing a single sea-level rise forecast for the state’s entire coastline, the scientists will issue separate projections for four different geographic zones within the state.
“I don’t know anyone who’s gone that far,” said Skip Stiles, executive director of Wetlands Watch in Norfolk, Va. “In Virginia, that’s been a big head-scratcher for us.”
The segmented projections indicate the North Carolina scientists’ growing sophistication – and caution – in issuing pronouncements related to climate change.
Their last prediction – in 2010, that North Carolina’s sea levels could rise 39 inches by century’s end – triggered a firestorm of protest from climate-change skeptics and coastal developers. The scientists’ range was 15.7 to 59.1 inches of sea-level rise by 2100.
This time, the scientists are limiting their forecast to 30 years and employing methodologies not used in their previous report, which could reduce tidal measures of North Carolina’s sea levels. Predicting for four separate zones was mandated by the state legislature after the political fallout from the 2010 forecast.
The cautious approach could scale back sea-level rise projections in North Carolina by including tidal gauge readings from southern parts of the state, which historically have had the state’s lowest sea-level measures.
North Carolina’s final projection could be lower than those issued by states with different approaches. According to an early draft of their report, the scientists are projecting a maximum potential sea level rise of 12.3 inches in Duck by 2045, a figure that could change as the draft report is revised. In neighboring Virginia, however, authorities are preparing for an 18-inch sea-level rise by midcentury, Stiles said.
North Carolina’s approach is a relief to Dave Burton, an adviser to NC-20, a group of coastal developers and climate-change skeptics who say sea-level rise projections by the United Nation’s Intergovernmental Panel on Climate Change are based more on ideology than on science.
“I am hopeful that it will be a substantial improvement,” said Burton, a Cary computer consultant.
Burton said the IPCC process is a “sham” and said he wishes North Carolina’s science panel gave less weight to the IPCC findings, which form the basis of the science panel’s estimates.
At its Monday meeting in New Bern, the science panel, working under the auspices of the N.C. Coastal Resources Commission, will review its methodology and make final adjustments ahead of a Dec. 31 deadline to issue its report. The report will be circulated among other scientists in January, put out for public comment March 31 and submitted to the state legislature March 1, 2016.
North Carolina’s legislature in 2012 barred any state agency from adopting a rule or policy based on any sea-level forecast other than the Coastal Resources Commission’s projections and said the CRC can’t adopt the science panel’s findings until July 2016.
That law makes the science panel’s conclusions the de facto basis of any future North Carolina policy for building roads, homes, bridges and for other planning decisions. The science panel is responsible for issuing “rolling” 30-year projections every five years.
In their early draft report, the scientists say sea levels could rise as much as 3 inches higher around Nags Head and Kitty Hawk than in the Wilmington area.
The early draft report says sea-level rise in Duck could be between 4.4 inches and 12.3 inches. In Southport, the range is projected from 1.9 inches to 8.7 inches. Those figures could change between Monday and Dec. 31.
The difference between sea levels in the northern and southern ends of the state are due to shifting geologic masses that are descending at a faster rate in the north. The tectonic shifts are caused by the melting of glaciers in the last ice age, and the gradual compression of sediments the glaciers deposited on North Carolina’s northern coast.
These trends play out over millennia and can be measured by geologists today.
“The historical rate of sea-level rise at the U.S. Army Corps of Engineers research pier in Duck has been a little more than the thickness of 2 nickels – stacked flat, on top of one another – per year,” science panelist Spencer Rogers wrote in a science blog post in 2012.
Rogers is a coastal construction and erosion specialist with N.C. Sea Grant, a coastal research and educational program in Wilmington.
Dredging a factor
In its 2010 report, the science panel based its single statewide estimate on tidal readings in one location, the town of Duck, near Nags Head. Because the state’s geologic land mass is sinking faster in Duck than anywhere else in the state, Duck has posted the highest levels of relative sea-level rise.
This time, however, the scientists are including readings from the Wilmington area, more than 200 miles south of Duck. The Wilmington-Southport area has the lowest tidal gauge measures for sea-level rise along the entire Atlantic coast.
Still, the Wilmington area is an important location to measure high tides, because that part of the state has tide gauge data going back to 1935, whereas Duck’s readings go back only to 1978 and are statistically less reliable.
Wilmington was excluded from the science panel’s 2010 report because the tidal gauge readings there are skewed by dredging in the Cape Fear River. This time, however, the science panel will make adjustments for the dredging impacts so that Wilmington can be factored in to the state’s sea-level rise report.
Dredging waterways inflates high-tide readings because so much more water rushes into the enlarged river channel. The Cape Fear’s 44-foot depth at the mouth is three times its original depth after more than a century of dredging.