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Subject: Global Warming's Effect On Sea Level Reexamined; Study Says Peril May Have
Date: Thu, 29 Oct 92 04:29:59 EST
Message-ID: <26.1992Oct29.042959@AmeriCast.com>

Global Warming's Effect On Sea Level Reexamined; Study Says Peril
May Have Been Understated<By Boyce Rensberger<Washington Post
Staff Writer=

The risk of a catastrophic rise in sea level as a result of glo-
bal warming could be higher than previously estimated, according
to a report in today's edition of Nature, the British scientific
journal.

The new analysis conflicts with previous studies. But if it is
right, and if global warming continues to increase for several
decades, the scientists say Earth's climate could heat up enough
to melt a large part of Antarctica's ice sheet, sending the melt
water into the oceans.

If all 7 million cubic miles of ice now resting on the continent
of Antarctica were to melt and flow into the ocean, it would
raise the sea level by 215 feet.

The threat of even a modest meltdown has been a favorite element
of the more alarmist scenarios of global warming. But it was
largely laid to rest in recent years after various analyses
showed that global warming might actually do the opposite: cause
increased snowfall that would remove water from the oceans and
build up the ice sheet. Moreover, there was evidence that the An-
tarctic ice sheet had been fairly stable since it formed about 14
million years ago, despite subsequent cycles of global warming
and cooling.

The new analysis, which is likely to revive those earlier fears,
is based on the discovery of evidence that suggests the ice
sheet, far from being stable, largely melted away about 3 million
years ago - just at a time when global temperatures were only a
few degrees warmer than they are now.

The new evidence was obtained by Peter J. Barrett of the Victoria
University of Wellington, New Zealand and colleagues. They have
shown that some marine fossils found in glacial debris high in
the Transantarctic Mountains belong to species known to have ex-
isted only about 3 million years ago. The fossils, remains of
now-extinct  microscopic creatures called diatoms, could not have
been deposited there unless the ice was gone and an ocean with a
higher level covered much of Antarctica.

The fossils were first found in 1984 and their age was presumed
to be the same as that of an identical combination of fossils
found elsewhere in deposits whose antiquity was well established.
But because this implied that the ice sheet melted 3 million
years ago, it conflicted with the evidence for stability and was
not widely accepted.

Now, however, Barrett and his colleagues have confirmed the date
by an independent method.  They found a layer of volcanic ash
amid the fossil deposits and determined by a well-accepted method
that certain minerals in the ash were formed in an eruption about
3 million years ago.

According to David Sugden of the University of Edinburgh, who has
also researched the question, Barrett's confirmation of the fos-
sils' age raises a serious challenge to the idea that the ice
sheet has been stable. In a commentary in the same issue of Na-
ture, Sugden said the clash of views has produced an "impasse"
that can only be solved by finding an error in the assumptions
underlying one of the alternative scenarios.

Evidence against an ancient meltdown is considerable, Sugden
said. For one thing, there is no sign of the land surface erosion
that would have resulted from such massive melting and outflow of
water. Instead, the land has geologic features indicating it was
scoured by glaciers that stayed frozen as they scraped their way
down slopes to the sea, where the ice broke off to form icebergs.

Also, Sugden wrote, 10 Fahrenheit of warming - the amount of in-
crease many experts say could happen over the next century if
global warming continues - would not cause major change. An-
tarctica would have had to warm by a year-round average of 70 to
melt the ice sheet all the way to the interior of the continent.
He said the far more modest warming that appears to have happened
3 million years ago should have enlarged the ice sheet through
increased snowfall.<02:21 10-29C9999-----

Copyright 1992, The Washington Post.  This story is from the
Washington Post's Capitol Edition On-Line and is not to be ar-
chived or redistributed.

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poration (usa@AmeriCast.COM)