Beach Erosion, Rodanthe, North Carolina – Outer Banks
Global sea level rise has more than doubled in the last 30 years from 2.1 mm per year in 1992 to 4.5 mm per year in 2024, with most of the rise happening later in the period (Hamlington 2024). The Outer Banks of North Carolina however, along with much of the middle and lower East Coast and Gulf of Mexico, are seeing some of the highest sea level rise rates in the world at 10 mm per year. (Dangedorf 2023). The sea level rise here that is more than double the global average comes from two effects. Natural subsidence after the last ice age is happening because of uplift beneath the former Laurentide Ice Sheet that was centered over Hudson Bay and extended down to New Jersey. When the ice sheet was still here, it was so heavy it depressed the Earth’s mantle and around the edges of the ice sheet, land rose as it was literally forces our from under the ice. Now that the ice is gone, the land around the former edge of the ice sheet is falling, including the area of the OUter Banks. this is the long-term subsidence that has created the ongoing erosions at Rodanthe and all along the Outer Banks.
Most of the sea level rise beyond the average global rise from melting ice and warming and expanding ocean water is coming from slow down of the Atlantic meridional overturning circulation, of which the Gulf Stream is a part. Cool freshwater melt from Greenland and the Arctic has accumulated south of Greenland of of Newfoundland and as its salt content is lower than that in the Atlantic, it floats as a surface layer and literally blocks the path of flow of the Gulf Stream. this acts like a dam, where upstream the water backs up and adds to sea level rise.
Some areas like Rodanthe, have seen erosion for generations, but it is the rate of erosion today that is making the difference. If we do not restore our climate, sea level rise will not only continue to increase, but it will increase at an ever increasing rate because of degradation that has already occurred to our ice sheets. The really good news though, is that because about half of observed sea level rise is from expanding and warming waters, if we restore our climate back to within it’s natural variation, some of the expansion will be eliminated as we cool our oceans. More will also be eliminated as melt from Greenland is reduced and the dam of fresh melt water off New Foundland is eliminated.
