WASHINGTON (AP) — Sea level has been rising significantly over the past
century of global warming, according to a study that offers the most
detailed look yet at the changes in ocean levels during the last 2,100
The researchers found that since the late 19th century — as the world became
industrialized — sea level has risen more than 2 millimeters per year, on
average. That’s a bit less than one-tenth of an inch, but it adds up over
It will lead to land loss, more flooding and saltwater invading bodies of
fresh water, said lead researcher Benjamin Horton whose team examined
sediment from North Carolina’s Outer Banks. He directs the Sea Level
Research Laboratory at the University of Pennsylvania.
The predicted effects he cites aren’t new and are predicted by many climate
scientists. But outside experts say the research verifies increasing sea
level rise compared to previous centuries.
Kenneth Miller, chairman of the Department of Earth and Planetary Sciences
at Rutgers University, called the new report significant.
“This is a very important contribution because it firmly establishes that
the rise in sea level in the 20th century is unprecedented for the recent
geologic past,” said Miller, who was not part of the research team. Miller
said he recently advised New Jersey Gov. Chris Christie that the state needs
to plan for a sea level rise of about 3 feet by the end of the century.
Horton said rising temperatures are the reason behind the higher sea level.
Looking back in history, the researchers found that sea level was relatively
stable from 100 B.C. to A.D. 950. Then, during a warm climate period
beginning in the 11th century, sea level rose by about half a millimeter per
year for 400 years. That was followed by a second period of stable sea level
associated with a cooler period, known as the Little Ice Age, which
persisted until the late 19th century.
Rising sea levels are among the hazards that concern environmentalists and
governments with increasing global temperatures caused by “greenhouse” gases
like carbon dioxide from burning fossil fuels like coal and oil over the
last century or so.
Although melting icebergs floating on the sea won’t change sea level, there
are millions of tons of ice piled up on land in Greenland, Antarctica and
elsewhere. Melting that ice would have a major impact by raising ocean
The result could include flooding in highly populated coastal cities and
greater storm damage in oceanfront communities.
While the new study does not predict the future, Horton pointed out that it
does show “there is a very close link between sea level and temperature. So
for the 21st century when temperatures will rise, so will sea level.”
Two of his co-authors calculated in an earlier paper that sea level could
rise by between 30 and 75 inches by the end of this century. And it might
even rise faster than that, Martin Vermeer of Aalto University in Finland
and Stefan Rahmstorf of Germany’s Potsdam Institute for Climate Impact
reported in 2009.
“Accurate estimates of past sea-level variability provide a context for such
projections,” co-author Andrew Kemp of Yale University’s Climate and Energy
Institute said in a statement.
Horton’s team studied sediment cores from salt marshes at Sand Point and
Tump Point on the North Carolina coast to develop their calculations of
sea-level change over the two millennia. They analyzed microfossils in the
cores and the age of the cores was estimated using radiocarbon dating and
For the years since tide gauges have been installed, those findings closely
track the results from the study, the researchers noted.
While Horton’s report is the first to produce a continuous record of the
past 2,000 years “other studies show similar changes, especially concerning
the acceleration in sea level rise in the 20th century,” Miller said.