File spoon-archives/anarchy-list.archive/anarchy-list_2003/anarchy-list.0302, message 428


From: "Dave Coull" <coull2-AT-btinternet.com>
Subject: RE: Gulf Stream
Date: Sat, 22 Feb 2003 01:12:12 -0000




Philadelphia Enquirer

 Posted on Sun, Dec. 08, 2002

After mild winters, a possible sea change
Some say a freshwater crimp in the Gulf Stream could bring a sudden shift to
biting cold.
By Anthony R. Wood
Inquirer Staff Writer

Scientists have been warning that the Earth is slowly heating up, that the
recent run of gentle winters in the United States is no fluke, but the
warm-up to the big meltdown.

Now, however, comes a chilling prediction from some of the same experts.
Before the climate gets balmier, they say, it could take a sudden turn
toward the frigid - and stay that way for decades, if not centuries.

In the Northeast, subzero temperatures could become standard winter fare,
filling rivers with ice chunks, cutting short the growing season, and
altering bird migrations. The cold and snow of the last week would feel like
spring break.

Behind that brutal scenario is a baffling ocean phenomenon that experts have
watched with rising angst: an expanding mass of freshwater in the usually
salty North Atlantic that has spread alarmingly in the last seven years. It
now reaches south from Greenland to just off the coast of the Carolinas, an
area of 15 million square miles.

If the buildup continues, they say, it could impede the Gulf Stream, a major
climate-maker that transports warm air to northern latitudes in winter. Were
that critical current to be slowed by the freshwater, let alone stopped,
average winter temperatures in the Northeastern United States and in Western
Europe could abruptly plummet 10 degrees - a change not experienced by
anyone alive today. A five-degree drop would be in store for the rest of the
States.

Exactly when it might occur, scientists generally are loath to speculate.

"None of us could tell you whether that event happens next year or 100 years
from now," said Raymond W. Schmitt Jr., senior scientist at the Woods Hole
Oceanographic Institution in Massachusetts, which has taken the lead in
studying the freshwater pool.

Researchers find themselves toeing a fine line between informing the public
and setting off a panic, Schmitt added. The U.N. committee on global warming
has put out the reassuring word that "such a shutdown is unlikely by 2100."
But John Gagosian, head of Woods Hole, had not even cold comfort to offer in
a recent paper.

"In just the past year, we have seen ominous signs that we may be headed
toward a potentially dangerous threshold," Gagosian wrote. "If we cross it,
Earth's climate could switch gears and jump very rapidly - not gradually -
into a completely different mode of operation."

One climate scientist suspects the Gulf Stream already is slowing down. At a
time when other glaciers around the world are in retreat, the Scandinavian
glacier has been growing. Andrew Weaver, of the University of Victoria,
British Columbia, says it may be the result of less warm air reaching that
far corner of the North Atlantic.

The prospect of a deep freeze, whether sooner or later, so concerns the
British government that it is sinking $30 million into figuring out what's
going on in The Pond. For while no one disputes the freshening is real, no
one is sure why it is happening.

Some researchers believe that, ironically, global warming could be to blame,
that melting Greenland glaciers and Arctic sea ice could be diluting the
salt water of the North Atlantic. Others theorize it could be a phase in a
natural cycle, one that ice-core evidence suggests might have happened
several times in the last 100,000 years - and perhaps as recently as
America's colonial era.

Oceans are turbulent, chaotic places, and their circulation is at least as
complex as the atmosphere's.

The Gulf Stream, which originates in the Caribbean, is no exception.
Oceanographers typically describe it as part of a "conveyor belt," because
in order to keep the current moving, the cold, salty water in the North
Atlantic must sink beneath it. That creates a void that is filled by the
rush of more Gulf Stream water. And so it moves north-northeast toward
Iceland at about 5 m.p.h., warming the overlying atmosphere for more than
2,000 miles.

The heated air moderates the frigid blasts out of Canada before they can
reach London, Paris or Rome. Without the Gulf Stream, London would feel like
Montreal, but gloomier.

Fresher water is a threat to the conveyor because it is lighter and sinks so
slowly that the Gulf Stream could sputter and even stop.

"If you don't sink that [cold] water and move it into the south, there's no
reason for the Gulf Stream to move the warm water to the north," said James
Wright, a Rutgers University paleoceanographer. The current "would turn
toward Portugal and go to the Canary Islands."

Even subtle changes in salinity can have a substantial effect on the rate at
which water sinks, said Weaver, of the University of Victoria. On average, a
gallon of seawater contains 4.7 ounces of salt. Even the freshest water in
the ocean still has about 4.2 ounces per gallon - far from potable, but
fresh enough to potentially affect the Gulf Stream.

Conveyor-belt disruptions and sudden climate changes are nothing new - only
the realization that they have occurred, says Richard B. Alley, a professor
of geosciences at Pennsylvania State University.

Conventional wisdom used to hold that climate change, like aging, happened
gradually. In the last 15 years, however, researchers studying ice cores
dating back 100,000 years have documented sudden shifts.

"Large, abrupt and widespread climate changes occurred repeatedly in the
past across most of the Earth, and many followed closely after freshening of
the North Atlantic," said Alley, who is also chairman of the National
Research Council's Committee on Abrupt Climate Change, which published a
report last spring.

Perhaps the most famous of these was the "Younger Dryas" event, so named for
the Arctic shrub that appeared in temperate European climes during a
dramatic cooldown about 12,000 years ago, 6,000 years after the last Ice
Age. And it happened in a hurry, a matter of just a few years.

Changes in the Gulf Stream also are suspect in the onset of the so-called
Little Ice Age, which began in the 15th century and ended about 1850. That
coincided with Gen. George Washington's encampment at Valley Forge during
the fatally frigid winter of 1777-78; the winter of 1779-80 was even worse.
It also encompassed the era of Washington Irving and frosty images of
skaters on the lower Hudson in December. No one skates there these days.

While abrupt shifts may be nothing new, this one would be unprecedented in
one important respect: Science is trying to get to the bottom of it. But
even as researchers measure the freshwater mass by dropping instrument packs
into the ocean, one thing is certain: They won't be able to stop it.

Any human effort to control the buildup, Weaver said, would be "like one
person standing on a railroad track trying to stop a train."




   

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