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Tempered estimates in updated sea level rise report

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Rising sea levels might not pose an immediate concern for residents of southeastern North Carolina. Preliminary predictions of a group of local scientists and engineers suggest the waters off the coast of Wilmington could rise 2 to 5 inches over the next 30 years as reported in a working draft of an updated sea level rise report compiled by the N.C. Coastal Resources Commission Science Panel, compared to a 2010 report’s statewide estimate of 39 inches by 2100.

The state-mandated update relies more heavily on historical data pulled from five National Oceanographic and Atmospheric Administration tide gauges to offer four distinct regional predictions. Higher levels of sea rise are predicted for the coast north of Cape Hatteras, due to land subsidence and changes in the speed and position of the Gulf Stream, yielding a higher range of 6 to 12 inches of rise at Duck, N.C., where the U.S. Army Corps of Engineers conducts a research pier.

The most modest predictions in the draft report follow the rate historically exhibited in the tide gauge data, projecting 2 inches of rise in Wilmington and 6 inches of rise in Duck over the next 30 years.

The report provides two other predictions that account for the influence of greenhouse gas emissions, considered the driving force of climate change by many scientists, using the latest numbers from the Intergovernmental Panel on Climate Change, an organization created by the United Nations.

The science panel’s current report predicts 4 inches of sea level rise in Wilmington and 11 inches of sea level rise in Duck over the next 30 years if greenhouse gas emissions are curbed, and 5 inches in Wilmington and 12 inches in Duck if emissions continue at peak concentration.

Coastal Resources Commission Chairman Frank Gorham said he is pleased with the range of scenarios and predictions offered in the panel’s draft report, which will be sent for peer review by Dec. 31. Gorham hoped to create a credible report more easily accepted by coastal communities than its predecessor — a goal he said was partially achieved by limiting the scope of the predictions from 90 years to a rolling 30-year time frame. The pared down predictions do not reflect acceleration in sea level rise expected around 2100, known as the hockey stick effect.

“We’ve limited it to 30 years. The 30 years doesn’t show a hockey stick,” Gorham said. “We’re going to do this every five years. If five years from now, we start to see a tendency of a hockey stick, then we have to give much more credibility to the upper [greenhouse gas emission] case.”

Current data does not suggest a rapid acceleration, said science panel member and N.C. Sea Grant construction and erosion specialist Spencer Rogers, but there is a “reasonably good chance” of acceleration. Rogers said the required five-year updates will allow the panel to act once locally collected data suggests acceleration.

“The five-year update is very important because, in order to predict the future, we really need some evidence that acceleration is occurring, not that it might occur,” Rogers said. “The numbers in the 30-year projection are relatively small compared to the 39 inches in the 90-year projection from the last report. That makes it even more important that we update it.”

Dustin Chicurel-Bayard, N.C. Sierra Club communications director, said long-range predictions are needed to allow residents to both prepare for the impact of higher sea levels and take steps to control sources of the predicted acceleration.

“It’s becoming clear that the accelerated rate of sea level rise is going to happen at the end of that 100-year period. That is something we should be taking into account, but it should also shape the way that we approach clean energy, reducing carbon emissions and making sure we do what we can to curb climate change, which is the ultimate driving force behind this,” Chicurel-Bayard said.

Tyler Newman, Business Alliance for a Sound Economy senior government affairs director, said he is comfortable with the draft report’s conclusion. He attended many of the science panel meetings to better understand what data was used and how it was interpreted to arrive at predictions that will inform coastal building standards and infrastructure development.

“All of the cards are on the table and they’re working forward on putting something together that we can all collectively get behind,” Newman said.

Gorham said he does not plan to use the final report to implement new coast-wide rules or policies.

“This is not a mandatory plan. I’m not going to tell Nags Head that they have to use any particular case. I’m going to give them the opportunity to see the various cases . . .  but if Nags Head wants to have farther setbacks and wants to have farther size limitations? Go for it,” Gorham said.

The draft report will be sent to Dr. Robert Dean, professor emeritus in the University of Florida’s coastal and oceanographic engineering program, and Dr. James Houston, a retired U.S. Army Corps of Engineers engineer, for peer review. After the report emerges from peer review, it will be available for public comment before a final report is submitted to the N.C. General Assembly by March 1, 2016.

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