North Carolina scientists on a panel tasked with predicting future sea levels expect the Atlantic Ocean to rise between 4 inches and 11 inches on the state’s coast over the next three decades.
But the effect of rising sea levels will be much less pronounced in Wilmington than in northern coastal areas, likely resulting in as many as four sea-level predictions for different parts of the North Carolina’s coastline.
The science panel, which met Wednesday, must issue its projections by Dec. 31. The members of the panel are trying to determine how best to calculate estimates of rising sea levels with estimates of rising and falling land masses. The interaction of simultaneous oceanic and terrestrial shifts will determine which coastal areas will be more prone to sporadic flooding and hurricane storm surges as ocean levels rise.
The panel, working at the behest of the N.C. Coastal Resources Commission, is limited by a 2012 state law to a 30-year projection out to 2045. State lawmakers imposed the limit after the panel projected a 39-inch sea-level rise in a 2010 report that sparked concern from climate change skeptics and coastal developers.
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By limiting their work to a 30-year horizon, the scientists are extrapolating past sea level changes without taking into account the dramatic increase anticipated in the second half of the century. As a result, North Carolina’s projection will be consistent with sea level rise documented over past decades, not with the sudden acceleration some fear.
“We’re getting lost in the inches here,” said William Birkemeier, a panelist who retired last year from the U.S. Army Corps of Engineers after serving as a coastal engineer for the research station in Duck.
“What’s the number at which you don’t want a hospital to flood?” he said. “Is it the sea level? No. It’s the 16 feet of Hurricane Hazel storm surge plus 1 (foot), and a safety factor.”
The panel’s report will be released for public comment in March and is due to the General Assembly in March 2016. The report is being prepared for planning purposes and as a policy guide, but in North Carolina, the subject of man-made climate change is as much about science and statistics as it is politics and ideology.
The scientists are not conducting their own computer models but rather adapting hundreds of existing studies to North Carolina shoreline. Because the current report is an update from their 2010 report, their projection will likely be consistent with the previous estimate, which projected a 30-year sea-level rise of about 8 inches.
“What this group is trying to do is figure out how the global picture relates to North Carolina,” Birkemeier said.
The science panelists spent five hours Wednesday reviewing data projections, calculations and models as they approach an Oct. 24 internal deadline to prepare their first draft for review among themselves. The scientists, who meet monthly, held their discussion at the Craven County Cooperative Extension office in New Bern about two hours east of Raleigh.
Vagaries in North Carolina’s geology are causing southern sections of the state’s shoreline to rise about 0.24 millimeter a year, according to some estimates, while the state’s northern coast is sinking at a rate of 1 millimeter annually, said science panelist Greg “Rudi” Rudolph, shore protection manager in Carteret County.
“This is why sea level is rising at different rates,” Rudolph said.
According to data presented by James “Tom” Jarrett, a Wilmington engineer, sea levels are also rising but at different rates, depending on where the measurements are taken and over what period of time. Determining a reliable average, and calculating the relationship between shifting land and sea levels, lies at the heart of the science panel’s task.
The ocean measures come from tidal gauges along the coast. Sea-level rise has been measured at 6.7 millimeters a year at Sewell’s Point, Va., nearly 5 millimeters annually in Duck, 3.2 millimeters a year at Morehead City, 3.3 millimeters a year at the former Hatteras fishing pier, 0.5 millimeter a year in Wilmington and 0.009 millimeter a year in Springmaid Pier, S.C.
The records vary for the same place, depending on the period the measurements were taken.
“What’s important, at least superficially, is there is a pattern there,” said Stan Riggs, a geologist at East Carolina University.