Oceans To Fall, Not Rise, Over Millions of Years
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 metres (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
metres.
"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 metres 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
centimetres a century -- irrelevant when the UN 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 the
seas.
Antarctica and Greenland now contain enough ice to raise
sea levels by 50 metres 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 metres rather than the projected 120.
The study challenges past belief that sea levels might
have been only 40 metres 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 metres in the period, skewing the readings.
-- For Reuters latest environment blogs go to: http://blogs.reuters.com/environment/
(Editing by Andrew Roche)
Story by Alister Doyle
Story Date: 7/3/2008
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