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"Mini Ice Age" May Be Coming Soon, Sea Study Warns

James Owen
for National Geographic News
November 30, 2005
 
Chilling new evidence from the Atlantic Ocean is raising fears that
western Europe could soon be gripped by a mini ice age.

Global warming is slowing down the ocean current that carries warm waters from the tropics to the North Atlantic, scientists say.

In the 2004 eco-disaster movie The Day After Tomorrow, a similar scenario spurred sudden, catastrophic climate change, with much of Europe and the United Stated transformed into frozen wastelands within days.

That scenario remains far-fetched. But British scientists say their new findings indicate that the threat looks all too real for northern Europe and marine animals.

Researchers at the National Oceanography Centre in Southampton, England, found that the flow of warm ocean currents toward northwest Europe has declined by 30 percent since the 1950s.

The research, to be published tomorrow in the journal Nature, is based on data collected in a great swath of the Atlantic between West Africa and Florida.

Led by oceanographer Harry Bryden, the team detected other key changes in the overall Atlantic circulation system.

For one thing, there appears to be a 50 percent reduction in the amount of cold, deep water flowing from the North Atlantic to the tropics, the team says.

Also, the researchers found a 50 percent increase in currents circulating within subtropical seas without reaching higher latitudes. More warm waters, that is, are staying put in the tropics.

The study supports computer model predictions suggesting that global warming will switch off the North Atlantic current in the next 50 to 100 years. (See "Global Warming May Alter Atlantic Currents, Study Says.")

"This provides the first evidence that such a slowdown is actually occurring," said Detlef Quadfasel, oceanographer at the University of Hamburg in Germany.

Important Observation

Quadfasel, who was not involved in the study, says the British team's findings aren't conclusive. They are, he said, based on limited samples of water salinity and temperature collected over five decades.

Still, Quadfasel said, "This observation is really important, even though it's at the limit of accuracy. The main message, I think, is right."

Many scientists have predicted this effect. Global warming already appears to be injecting more fresh water into polar seas due to increased precipitation and the melting of the Greenland ice cap.

This freshening of the North Atlantic current makes its waters less dense—so they don't sink down to depths at which they would then be transported back south.

As result, the circulation stalls, with warmer water no longer being drawn north.

Measurements of salinity levels in the North Atlantic over the last 50 years show "a significant trend toward lower salinity all over the place," Quadfasel said.

Evidence from prehistoric times shows that it is possible for northern air temperatures to drop by 10ºC (18ºF) within decades.

These abrupt changes are intimately linked to switches in ocean circulation, experts say.

Full Stop?

Some computer models predict an abrupt stop to the North Atlantic current sometime in the next hundred years. The current is responsible for Europe's relatively mild climate.

"Personally I don't think it's going to happen in the next few years, but it's like a nuclear power plant—you've got to look at the risks, even if you don't expect the thing to blow up next week," Quadfasel said.

If the current does stop, he says, it would have devastating effects on northwest Europe. The freezing conditions would affect everything from agriculture to energy demand.

Marine life could also be seriously affected, according to Andreas Schmittner, assistant professor at Oregon State University's College of Oceanic and Atmospheric Sciences.

Stalling of the North Atlantic circulation would halt the flow of nutrients from the deep ocean. "Plankton abundance will strongly decline," Schmittner said.

"Since plankton builds the base of the ocean food chain, animals higher up the chain—such as fish, squid and whales—can also be expected to suffer," he said.

Such impacts would not be confined to the Atlantic Ocean, he adds. Water that sinks in the North Atlantic resurfaces in the Indian and Pacific Oceans and the seas surrounding Antarctica.

"Reduced sinking leads to reduced upwelling of nutrient-rich waters and hence slower growth of algae and other plankton," he said.

How Real? How Soon?

But Schmittner says a Day After Tomorrow scenario isn't likely to be appearing anywhere near you soon.

"There is no reason for immediate concern or panic," he said.

It's still too early to say whether sea changes identified in the new study are part of the ocean's natural variability or the first signs a decline caused by human-induced global warming, he said.

"I received a phone call a few weeks ago from a concerned citizen who plans to sell his property and move abroad because of a possible collapse of the Atlantic overturning circulation," Schmittner added.

"Such reactions are clearly unwarranted."

And what does Quadfasel, the German oceanographer, think of Hollywood's cautionary eco-tale?

"Basically I thought the movie was okay. What was wrong was the timescale. Such things don't happen within a couple of days," Quadfasel said.

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