OSLO Sea levels are set to fall over millions
of years, making the current rise blamed on climate change a
brief interruption of an ancient geological trend, scientists
said on Thursday.
They said oceans were getting deeper and sea levels had
fallen by about 170 meters (560 ft) since the Cretaceous period
80 million years ago when dinosaurs lived. Previously, the
little-understood fall had been estimated at 40 to 250 meters.
"The ocean floor has got on average older and gone down and
so the sea level has also fallen," said Bernhard Steinberger at
the Geological Survey of Norway, one of five authors of a
report in the journal Science.
"The trend will continue," he told Reuters.
A computer model based on improved understanding of shifts
of continent-sized tectonic plates in the earth's crust
projects more deepening of the ocean floor and a further sea
level decline of 120 meters in 80 million years' time.
If sea levels were to fall that much now, Russia would be
connected to Alaska by land over what is now the Bering Strait,
Britain would be part of mainland Europe and Australia and
Papua island would be the same landmass.
The study aids understanding of sea levels by showing that
geology has played a big role alongside ice ages, which can
suck vast amounts of water from the oceans onto land.
DOWN NOT UP
"If we humans still exist in 10, 20 or 50 million years,
irrespective of how ice caps are waxing and waning, the long
term ... is that sea level will drop, not rise," said lead
author Dietmar Muller of the University of Sydney.
Over time, Muller told Science in a podcast interview there
would be fewer mid-ocean ridges and a shift to more deep plains
in the oceans as continents shifted. The Atlantic would widen
and the Pacific shrink.
Still, the projected rate of fall works out at 0.015
centimeters a century -- irrelevant when the U.N. Climate Panel
estimates that seas will rise by 18-59 cms by 2100 because of
global warming stoked by human use of fossil fuels.
"Compared to what is expected due to climate change, the
fall is negligible," said Steinberger. Cities from Miami to
Shanghai are threatened by rising seas that could also swamp
low-lying island nations in the Pacific.
Rising temperatures raise sea levels because water in the
oceans expands as it warms, and many glaciers are melting into
Antarctica and Greenland now contain enough ice to raise
sea levels by 50 meters if they all melted, the article said.
If all ice on land were gone in 80 million years' time, the net
drop in ocean levels would be 70 meters rather than the
The study challenges past belief that sea levels might have
been only 40 meters higher than today in the Cretaceous period
by arguing that measurements from New Jersey in the United
States had underestimated the fall.
It said that the New Jersey region had itself subsided by
105 to 180 meters in the period, skewing the readings.
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(Editing by Andrew Roche)