| By
Claude Morgan ENN
Coastal
sea levels have risen a foot in the past century. Scientists
expect them to rise still more.
The
culprit is global warming, say scientists. But just how
much of that global warming is fueled by natural events
and how much is manmade? That mystery is lighting another
fire: a scientific debate, which could change the face of
our shorelines.
The
seas are rising nearly one-tenth of an inch each year, fed
by rivers of melting glaciers and ice sheets around the
globe, according to scientists at the United States Geological
Survey.
At the
current rate of melting, warn many scientists, the seas
could rise another foot over the next 50 years. Iceland's
glaciers could disappear by 2200.
Scientists predict glaciers in
Iceland could melt by 2200 if the global warming trend continues.
"No
one can tell you that the sea level today is higher than
it was yesterday," says Jim Titus, project director
of sea level rise at the U.S. Environmental Protection Agency.
But by averaging historical data, says Titus, scientists
can literally watch the tide roll in over the centuries.
"Plain
ol' linear analysis of the record reveals that the sea is
clearly rising relative to the land," says Titus.
Couple
that with the melting of the world's glaciers and a rise
of the earth's atmospheric temperature and you have what
many scientists now believe is a cosmic dance of tide and
temperature older than the hills themselves.
Every
100,000 years or so, the earth settles in for an ice age,
taking its cue from changes in its orbit around the Sun.
During long, elliptical orbits, the earth cools, and water
is stored on the continents in the form of ice. Sea level
falls. During shorter, circular orbits, the earth warms
up, and the ice returns to the sea, causing a rise in sea
level. These warming spells, called interglacial periods,
typically last about 10,000 years.
"We're
about two thirds of the way through an interglacial period,
right now," says Richard Williams, an oceanographer
with the USGS at Woods Hole, Massachusetts. Keeping his
eye on the Holocene Epoch — the name scientists give
to the current warming spell — Williams counts the
droplets of water as they run from the ice to the sea.
"It
takes about 6,300 cubic miles of melting ice to raise the
sea level one inch," says Williams. "If the ice
sheets on Greenland melted, that alone could raise sea level
by 20 feet."
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