November 30, 2005

Key warming ocean current slowing down: scientists

By Jeremy Lovell

LONDON (Reuters) - The Atlantic Conveyor, a life-giving
ocean current that keeps northern Europe warm, is slowing down,
scientists said on Wednesday.

If the 30 percent slowdown seen over the past 12 years is
not just a blip, temperatures in northern Europe could drop
significantly, despite global warming, they added.

Scientists have long forecast that the Atlantic Conveyor
that carries warm surface water north and cold deep water back
to the equator could break down because of global warming.

According to the theory, rising air temperatures cause ice
caps to melt, making the water less salty and therefore less
dense so it can't sink and flow back south.

The scientists on Wednesday said this was the first time
that observations had put flesh on the bones of the theory.

"This is the first time we have observed a change in the
current on a human timescale," oceanographer Harry Bryden said,
noting that it had completely shut down during the ice ages.

But he said the latest figures were far from proving a
trend and that constant and long-term monitoring was needed.

"It is like a radiator heating the atmosphere and is too
important to leave to periodic observations," Bryden told a
news conference to flesh out a paper he co-authored in Nature
science journal.


The Hadley Center for Climate Prediction and Research has
calculated that if the current stopped, temperatures in
northern Europe could drop by up to six degrees centigrade in
20 years.

The latest figures, collated last year, are from a string
of monitoring devices at various depths in the Atlantic from
Morocco to Miami.

It was the fifth snapshot since 1957 taken in the same area
of the temperatures and currents in shallow, mid and deep

While measurements in 1981 and 1992 had shown little
change, those in 1998 and 2004 had shown a major shift, with
less of the warming Gulf Stream getting up to Greenland and
less of the cold, deep returning current coming back.

The so-called Atlantic Meridional Overturning Current is
known as the Atlantic Conveyor, of which the Gulf Stream is the
surface component.

"This is tantalizing evidence that there may be a large
change in ocean circulation under way that paradoxically could
cause regional cooling," said Phil Newton of Britain's
independent Natural Environment Research Council (NERC).

However, the scientists stressed that they could not be
completely sure what was driving the change or how it might
alter or be compensated for by winds that pick up the radiated
heat and circulate it.