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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