Studies show sea-level rise is accelerating off North Carolina – StarNewsOnline.com
New research reinforces what scientists and others have been warning about the ocean along the North Carolina coast: The sea is rising faster than in most other parts of the United States, and faster than what most scientists had expected.
“It’s very worrisome,” said Dr. Phil Bresnahan, an oceanographer at the University of North Carolina Wilmington. “I don’t think there’s any way around that conclusion.”
Sea-level rise is a natural phenomenon. But it is also an event that is being exacerbated by human actions, notably the pumping of greenhouse gases into the atmosphere that is, among other things, increasing the melting rate of the polar ice caps.
Scientists, including top researchers on the United Nations’ Intergovernmental Panel on Climate Change (IPCC) said there is little doubt that humans are the leading cause of global warming.
On Friday, the impact of climate change on the oceans was reinforced by the World Meteorological Organization, which said global sea levels are rising at more than double the pace they did during the first decade of measurements from 1993 to 2002, and hit a new record high last year.
The United Nations agency said extreme glacier melt and record ocean heat levels contributed to an average rise in sea levels of 4.62 millimeters (0.18 inches) a year between 2013 and 2022. That is about double the pace of the first decade on record, leading to a total increase of over 10 centimeters (3.93 inches) since the early 1990s.
The WMO is just the latest report to show that sea-level rise has been increasing in recent decades − and even more quickly in recent years − beyond what can be explained by just natural phenomenon.
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‘These rapid rates are unprecedented’
Closer to home, a recent study led by researchers from Tulane University found sea rise along the U.S. Southeast and Gulf coasts have reached record-breaking levels over the past 12 years.
The study, published late last month in the journal Nature Communications, found that researchers had detected rates of sea-level rise of about 0.5 inches a year since 2010. While that might not sound like a lot, the U.S. Environmental Protection Agency says average sea level has risen by 0.14 inches since the early 1990s.
“These rapid rates are unprecedented over at least the 20th century and they have been three times higher than the global average over the same period,” said Dr. Sönke Dangendorf, one of the study’s lead researchers and an assistant professor at Tulane, in a university release.
The scientists found that the accelerated sea-level rise ran from roughly Cape Hatteras to the Gulf of Mexico and into the North Atlantic and the Caribbean − an area known as the Subtropical Gyre. The paper theorized that the gyre, which is a rotating ocean current, has been altered by warming ocean temperatures − which expands water − and changing wind patterns.
The recent accelerated sea-level rise rates were a result of manmade climate change influences and a peak in weather-related variability, the researchers suggested. The rising seas should return to more normal levels as the weather variability moderates in the coming decades, as most climate models forecast.
“However, this is no reason to give the all clear,” said Dr. Torbjörn Törnqvist, the study’s co-author and a geologist at Tulane. “These high rates of sea-level rise have put even more stress on these vulnerable coastlines, particularly in Louisiana and Texas where the land is also sinking rapidly.”
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A range of factors
While the Tulane-led study took a macro look at the issue, annual research by the Virginia Institute of Marine Science 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 around the U.S. coast. Using tidal observations since 1969, VIMS has been analyzing tide-gauge data to forecast possible sea-level rise out to 2050. Gauges the researchers track in the Southeast include Norfolk, Va., Wilmington, Charleston, S.C., and Savannah, Ga.
For a fifth year in a row, Norfolk held 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 rising ocean levels over the past few years.
“The southern Mid-Atlantic area has been showing an acceleration rate over that time period that is a little bit higher from when we first started,” she said.
Mitchell said there could be a range of large-scale factors impacting why that’s happening, including increased ice sheet melting and changing circulation patterns. But because the tide gauges reflect very local signals, they also could be influenced 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 climate and geological conditions.
“A tide gauge is telling you what’s happening right there,” Mitchell said. “It doesn’t do a good job of telling you what’s happening 100 miles up the coast.”
That makes picking out one or two factors causing a change in rising water levels difficult, especially when trying to forecast sea levels decades out.
“But it’s a good context to have, especially when it comes to what we should be aiming for, say with local planning, in the short term,” Mitchell said. “It can help tell us if future flooding is going to 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” projects that the Port City will see an average sea-level rise of 0.52 meters (1.7 feet) over 1992 levels by 2050 based on historic tide gauge data. Wilmington’s NOAA tidal gauge is at the base of the Cape Fear Memorial Bridge.
But Mitchell said tides aren’t always uniform, meaning some months they are higher and other months they are lower. The report card forecasts some of Wilmington tides in 2050 could show an increase of 0.69 meters (2.26 feet).
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“Sea-level rise is a relatively slow crisis,” Mitchell said. “It’s not like a storm coming where you might only have several days to prepare for it.”
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 do we react to keep people and property out of harms way.
“It’s easy to speak as a scientist about what we see coming,” he said. “What we actually do about it is the much more challenging thing.”
Reporter Gareth McGrath can be reached at GMcGrath@Gannett.com or @GarethMcGrathSN on Twitter. This story was produced with financial support from 1Earth Fund and the Prentice Foundation. The USA TODAY Network maintains full editorial control of the work.