Seas rising faster along northern Outer Banks
By Frank Tursi
Coastal Review Online
state legislators still wading through the issue of rising seas, a new
federal report released yesterday seems to further muddy the water.
Contrary to what we heard from some legislators the last few weeks, not
only does the sea seem to be rising along the state’s northern coast,
but it's doing so at a rate three or four times faster than anyplace
else in the world.
That, at least, is one of the conclusions of a new study of sea-level
rise that the U.S. Geological Survey published yesterday in the journal
Nature Climate Change.
Analyzing information from tide gauges along the north and mid-Atlantic
coasts, agency researchers found that sea level along a 600-mile
stretch, from Cape Hatteras to north of Boston, has increased 2 to 3.7
millimeters a year, starting around 1990. That’s as much as 2.75 inches
during that span. The average global increase over the same period was
0.6 to 1.0 mm. a year, or about three-quarters of an inch total, the
If global temperatures continue to increase this century because of
global warming, the Atlantic Ocean in this region is expected to
continue to rise at a faster rate than it will elsewhere, the
researchers said. The sea along this stretch of coast, which contains
some of the country’s largest metropolitan areas and most densely
populated coastal landscapes, could rise 8 to more than 11 inches
higher than the global average by 2100, the research showed.
It's not just a faster rate, but at a faster pace, like a car on a
highway “jamming on the accelerator,” Asbury Sallenger Jr., an
oceanographer at the agency and the study’s lead author, told the
Seas will rise gradually over time, noted Peter Howd, an oceanographer
under contract with the USGS and one of the paper’s other authors, but
greater flooding from winter storms will be the first signs.
“People are starting to recognize that winter storms that used to pass
by without producing any flooding, all of sudden they are getting
flooding,” Howd said in an interview last week. “Where it’s really
going to hit home is that the storms that we get three or four times a
winter will start looking like the storms that we get every three or
SCIENCE AND POLITICS
The new research seems to counter arguments made by backers of a bill
that passed the N.C. Senate a couple of weeks ago. The bill was widely
interpreted as preventing the state from using the latest scientific
modeling when planning for future sea-level rise because of global
Warming atmospheric temperatures in the future are expected to push up
sea levels by melting ice sheets in Greenland and west Antarctica, and
because warmer water expands. Climatologists use sophisticated computer
models to predict how high the seas could get under different warming
After reviewing the consensus of those models, a panel of scientific
advisors told the state Coastal Resources Commission in 2010 to prepare
for a sea-level rise of 39 inches by 2100, or more than triple the
historic rate. Though the new research suggests adding a few more
inches to that total, the forecast was in line with those made by major
scientific organizations around the world and by several countries and
But the state report immediately came under fire from development
interests and some coastal counties. They feared that regulations to
protect against such a drastic rise in sea level would stifle economic
growth on the coast.
Critics also questioned the science behind the report. That was echoed
by sponsors of the Senate bill. The science of sea-level rise was
unsettled, they said, and the models were speculative at best. Credible
evidence exists, they insisted, that indicates sea levels haven’t risen
appreciably in the past 100 years.
The bill that passed the Senate would have forced the state to use
those historic rates when planning for what the ocean might do in the
future. Those long-term average rates of historic sea-level rise, when
extrapolated into the future, indicate the ocean might rise only 8
inches this century, not 39.
After being lampooned by commentators, scientists and writers around
the world, the bill died last week when the N.C. House refused to vote
on it. Representatives from both chambers are trying to devise a
The names of Robert Dean and James Houston came up often in the debate.
They are well-respected coastal engineers who studied data from tide
gauges and determined that long-term average sea-level rise for the
past 80 years has been negligible even though temperatures have risen.
The USGS researchers tried to replicate Dean and Houston’s findings by
using the same tide information from across North America, Howd noted.
To determine if the rate of rise has recently accelerated, though, they
analyzed smaller time segments of tide gauge data and in a way that
removed long-term trends associated with vertical land movements.
“Dean’s numbers are correct for what he calculated, the long-term
average acceleration over the last 80 years,” Howd explained. “That’s a
very different answer as to whether there’s any recent acceleration. We
just asked a different question.”
AMOC AND YOU
The answer they got has everything to do with the Atlantic meridional
overturning circulation, called AMOC by those who study such things.
It’s part of the oceans’ conveyor system, which constantly
redistributes heat and cold. AMOC carries warm water from the tropics
to high northern latitudes near the surface and returns cold water from
the north Atlantic in the deep ocean to the Southern Hemisphere. In
that way, a balance is achieved. The Gulf Stream is AMOC’s main highway
How AMOC does all this is complicated, involving water temperature,
salinity and density in the subpolar north Atlantic, but scientists
have long thought that a warming climate could affect the circulation.
The USGS study, though, may be the first to indicate that might be
happening already. The report shows that the sea-level rise “hotspot”
north of Cape Hatteras is consistent with the slowing of AMOC, Howd
So much water is flowing north in the Gulf Stream and at such a quick
pace that the core of the stream is two meters higher than the water at
the shoreline, Howd explained. “When the current slows down, the Gulf
Stream falls and the water levels increase at the coast. That’s the
simple answer, but it’s pretty complicated.”
The magnitude of this see-saw affect will be greater farther from the
Gulf Stream, Howd said. The Stream hugs the North Carolina coast before
veering east across the Atlantic north of Cape Hatteras. Howd and the
other researchers saw no evidence of accelerated sea-level rise above
the global average for much of the state’s coast. It became evident
north of the cape, he said, but the rate there was lower than it was
Because of its proximity to the Gulf Stream, the northern North
Carolina coast could expect to see seas rise at the low end of the
study’s estimates, about 8 inches above the global average by 2100,
Whatever they do in the future, the oceans won’t do it at the same rate
in every location, noted Marcia McNutt, the director of the USGS.
Differences in land movements, strength of ocean currents, water
temperatures and salinity can cause regional and local highs and lows
in sea level.
"Many people mistakenly think that the rate of sea-level rise is the
same everywhere as glaciers and ice caps melt, increasing the volume of
ocean water, but other effects can be as large or larger than the
so-called ‘eustatic’ rise,” she said. “As demonstrated in this study,
regional oceanographic contributions must be taken into account in
planning for what happens to coastal property.”
And it may not take years to feel the effects of rising seas, Sallenger said.
“Cities in the hotspot, like Norfolk, New York and Boston already
experience damaging floods during relatively low-intensity storms,” he
said in a press release. “Ongoing accelerated sea-level rise in the
hotspot will make coastal cities and surrounding areas increasingly
vulnerable to flooding by adding to the height that storm surge and
breaking waves reach on the coast.”
story is provided courtesy of Coastal Review Online, the coastal news
and features service of the N.C. Coastal Federation. You can read other
stories about the N.C. coast at www.nccoast.org.)