http://www.commondreams.org/headlines05/1201-03.htm
via - http://www.independent.co.uk/

Published on Thursday, December 1, 2005 by the Independent / UK
Fears of Big Freeze as Scientists Detect Slower Gulf Stream
by Steve Connor

The ocean "engine" that helps to drive the warm waters of the Gulf
Stream and keeps Britain relatively mild in winter has begun to slow
down, say scientists.

Measurements of ocean currents in the North Atlantic reveal that they
have weakened by about 30 per cent since 1992. The findings,
published in the journal Nature, fit computer predictions of what
would happen when Greenland glaciers begin to melt because of global
warming. The models suggest that extra freshwater released into the
North Atlantic could weaken ocean currents and even shut down the
Gulf Stream.

Britain benefits from the enormous amounts of heat - equivalent to
the output of a million power stations - carried from the Caribbean
by the Gulf Stream and the North Atlantic Drift, and a tailing off in
these currents could have a major impact on the country's climate.

Scientists estimate that the detected 30 per cent weakening of the
Atlantic currents could lead to a fall of about 1C in Britain's
average temperatures over the next 20 years.

They also warn that the weakening could be the first signs of an
accelerating trend that could eventually lead to a more drastic
change, including a complete shutdown of the currents. If this were
to happen, average temperatures in Britain could fall by between 4C
and 6C, leading to winter temperatures similar to Newfoundland in
Canada, which is on the same latitude as the UK but does not benefit
from the Gulf Stream.

Professor Harry Bryden, of the National Oceanography Centre at the
University of Southampton, said the ocean currents of the North
Atlantic acted as a conveyor belt that carried warm water at the
surface in one direction and transported cold, deep-water currents in
the other.

"It is a massive system that includes the Gulf Stream and it carries
heat northward out of the tropics into the northern Atlantic, warming
the atmosphere and helping to provide northern Europe with a moderate
climate," Professor Bryden said.

For the past 50 years, oceanographers have measured the strength of
these currents along a stretch of the North Atlantic situated at a
latitude of 25 degrees north of the equator, from Florida in the west
to the African coast in the east.

When they analysed that rate of ocean flow - measured in Sverdrups
(Sv), or a million tons of water flowing per second - they found that
in 1992 it was about 20Sv, but in 2004 it had fallen to 14Sv. "In
previous studies over the past 50 years, the overturning circulation
and heat transport across 25 degrees north were reasonably constant.
We were surprised that the circulation in 2004 was so different from
previous estimates," Professor Bryden said.

The study used data from an array of instruments anchored at 22
moorings, nine of which are positioned east of the Bahamas, four in
the mid-Atlantic and nine across the continental slope of east
Africa. Each mooring is anchored to the seabed on wires 5,000 metres
(16,400ft) long, and holds instruments that continuously record
salinity, temperature, pressure and current flow. Stuart Cunningham
of the National Oceanography Centre said: "Continuous monitoring
could alert us to potential rapid climate change."

© 2005 Independent News and Media Limited



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