Azara Blog: Ocean current in the Atlantic might bring cooler weather to Europe

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Date published: 2005/11/30

The BBC says:

Changes to ocean currents in the Atlantic may cool European weather within a few decades, scientists say.

Researchers from the UK's National Oceanography Centre say currents derived from the Gulf Stream are weakening, bringing less heat north.

Their conclusions, reported in the scientific journal Nature, are based on 50 years of Atlantic observations.

They say that European political leaders need to plan for a future which may be cooler rather than warmer.

The findings come from a British research project called Rapid, which aims to gather evidence relating to potentially fast climatic change in Europe.
...
Florida-based scientists monitor the northwards-flowing Gulf Stream, and have found it has remained roughly constant over the last 50 years.

The NOC researchers concentrated on the colder water flowing south; and they found that over the last half century, these currents have changed markedly.

"We saw a 30% decline in the southwards flow of deep cold water," said Harry Bryden.
...
The NOC researchers admit that the case is not yet proven.

The analysis involves only five sets of measurements, made in 1957, 1981, 1992 and 1998 from ships, and in 2004 from a line of research buoys tethered to the ocean floor.

Even if the trend is confirmed by further data, it could be down to natural variability rather than human-induced global temperature change.

"This issue of variability is very important," said Harry Bryden, "and we do not have any good grasp of it.

"Models can predict it, but we think we ought to go out and measure it."

Michael Schlesinger from the University of Illinois at Urbana-Champaign, a leading expert in models of climate and ocean circulation, believes that even with these caveats, the NOC team has probably come up with a link to human-induced climate change.

"The variability question is the right one to ask," he told the BBC News website, "but the phasing is wrong."

A decade ago Professor Schlesinger showed that the north Atlantic conveyor undergoes a natural 70-year cycle of strengthening and weakening.

"The Bryden measurements are out of phase with this cycle," he said.

"The natural cycle had a northern cooling until the mid-1970s and a warming afterwards, and here we see an apparent cooling."

He is also convinced by other details of the NOC measurements showing that the changes in the southerly underwater flow have occurred at great depths.

"The slowing down of the southward return occurs between 3,000 and 5,000m; and this more or less constitutes a smoking gun," he said.

So what does all this mean for European weather? Will it necessarily get colder - or will the apparent recent trend of warmer summers continue?

"If this trend persists," said Harry Bryden, "we will see a temperature change in northern latitudes, perhaps of a degree Celsius over a couple of decades."

But climate is a complex phenomenon; other factors could conspire, even so, to produce a net warming.

More grist for the mill. The main worry is that there are only five sets of measurements (and were the methodologies even identical?). Of course the media likes this kind of dramatic announcement, so play it all up. When young climate scientists start selling their houses in the UK and moving to the south of France then perhaps we should all start to have more confidence in these predictions. (Britain would not be uninhabitable but it would certainly be a much less desirable place to live.)

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