New research reinforces what scientists and others have warned about the ocean along the North Carolina coast: Seas are rising faster than in most other parts of the United States, and faster than most of scientists expected.
“It’s very concerning,” said Dr. Phil Bresnahan, an oceanographer at the University of North Carolina Wilmington. “I don’t think there is any way around that conclusion.”
Sea level rise is a natural phenomenon. But it’s also an event that is being exacerbated by human actions, especially the pumping of greenhouse gases into the atmosphere which, among other things, is increasing the rate of melting of the polar ice caps.
Scientists, including top researchers from the United Nations’ Intergovernmental Panel on Climate Change (IPCC), said there is no doubt that humans are the main cause of global warming.
The impact of climate change on the oceans was reinforced on Friday by the World Meteorological Organization, which said global sea levels were rising at more than double the rate of the first decade of measurements, from 1993 to 2002, and achieved a new record last year.
The UN agency said extreme glacier melt and record levels of ocean heat contributed to an average sea level rise of 4.62 millimeters (0.18 in) a year between 2013 and 2022. That’s about double the pace of the first decade on record, leading to a total increase of more than 10 centimeters (3.93 inches) since the early 1990s.
The WMO is just the latest report showing that sea level rise has increased in recent decades and even faster in recent years beyond what can be explained by a natural phenomenon alone.
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“These rapid rates are unprecedented”
Closer to home, a recent study by researchers at Tulane University found sea rise along the US Southeast and Gulf Coasts has reached record highs in the past 12 years.
The study, published late last month in the journal Nature Communications, found that researchers had observed rates of sea level rise of about 0.5 inches per year since 2010. While that may not sound like much, the agency for the U.S. Environmental Protection says mean sea level has risen 0.14 inches since the early 1990s.
“These rapid rates are unprecedented in at least the 20th century and were three times higher than the global average over the same period,” said Dr. Snke Dangendorf, a lead investigator on the study and an assistant professor at Tulane, in a university release.
The scientists found that the accelerated sea level rise ranged roughly from Cape Hatteras to the Gulf of Mexico and into the North Atlantic and Caribbean, an area known as the Subtropical Gyre. The paper theorized that the vortex, which is a rotating ocean current, has been altered by warming ocean temperatures which expands the water and changes wind patterns.
The recent rates of accelerated sea level rise were the result of the influences of human-induced climate change and a spike in climate-related variability, the researchers suggested. Sea level rise is expected to return to more normal levels as weather variability eases over the next few decades, as predicted by most climate models.
However, that’s not a reason to give the green light, said Dr. Torbjrn Trnqvist, study co-author and Tulane geologist. These high rates of sea level rise have put even more stress on these vulnerable coasts, particularly in Louisiana and Texas, where land is also sinking rapidly.
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A number of factors
While the Tulane-led study took a macroscopic look at the problem, the Virginia Institute of Marine Science’s annual research at William & Mary takes a more localized approach to studying sea level rise.
In March, the school released its latest sea level report cards for 32 tide gauge sites scattered along the U.S. coast. Using tidal observations since 1969, VIMS analyzed tide gauge data to predict possible sea level rise through 2050. Markers the researchers track in the Southeast include Norfolk, Virginia, Wilmington, Charleston, South Carolina and Savannah, Georgia.
For the fifth year in a row, Norfolk had the dubious honor of having the highest rate on the East Coast. Second was Sandy Hook in New Jersey, followed by Savannah.
Dr. Molly Mitchell, research assistant professor at VIMS, said the Carolinas have seen a significant acceleration in ocean level rise in recent years.
“The southern Mid-Atlantic area has shown a rate of acceleration over that time period that is a little bit higher since we started,” he said.
Mitchell said there could be a number of large-scale factors influencing why this is happening, including increased melting of ice sheets and changing circulation patterns. But because tide gauges reflect very local signals, they could also be affected by factors such as a change in water flows, drought, sinking land masses, a major problem in much of northeastern North Carolina, or other local climatic and geological conditions.
“A tide gauge tells you what’s happening right there,” Mitchell said. “He doesn’t do a good job of telling you what’s happening 100 miles up the coast.”
This makes it difficult to pinpoint one or two factors causing a change in water level rise, especially when trying to predict sea level decades from now.
“But it’s a good context to have, especially when it comes to what we should be aiming for, like with local planning, in the near term,” Mitchell said. “It can help tell us whether future flooding will be a nuisance or something more, like blocking an access road to a hospital.”
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“A Relatively Slow Crisis”
Wilmington’s sea level rise “report card” predicts the port city will see an average sea level rise of 0.52 meters (1.7 feet) above 1992 levels by 2050 based on historical data of the tide gauges. The Wilmington NOAA Tide Gauge is located at the base of the Cape Fear Memorial Bridge.
But Mitchell said the tides aren’t always uniform, meaning some months are higher and other months are lower. The report predicts that some of Wilmington’s tides in 2050 could show a rise of 0.69 meters (2.26 feet).
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“Sea level rise is a relatively slow-moving crisis,” Mitchell said. “It’s not like a coming storm where you might just have several days to prepare.”
Bresnahan, the UNCW oceanographer, said the factors contributing to sea level rise are complicated and complex. But the result of them on ocean levels are not.
The question then becomes how to react to keep people and property out of harm’s way.
“It’s easy to talk as a scientist about what we see coming,” he said. “What we actually do about it is the much more challenging thing.”
Journalist Gareth McGrath can be reached at GMcGrath@Gannett.com or @GarethMcGrathSN on Twitter. This story was produced with financial support from the 1Earth Fund and the Prentice Foundation. The USA TODAY Network retains full editorial control of the work.
