February 25, 2009 / 6:14 PM / 8 years ago

N.Atlantic climate shift see-saws on South: study

OSLO (Reuters) - Any abrupt climate changes in the North Atlantic region have a quick see-saw effect on the South Atlantic and affect weather around the globe rather than just locally, scientists said on Wednesday.

A study of ocean sediments from the last Ice Age in the South Atlantic backed theories that a sudden cooling or warming of the Northern Hemisphere causes an opposite effect in the south, they said.

Until now, scientists studying rapid temperature swings, caused by natural variations during the Ice Age that ended 10,000 years ago, lacked clear evidence of the see-saw link. Study of the chemical makeup of ocean sediments helped reconstruct ancient temperatures.

"Very large and abrupt changes in temperature recorded over Greenland and across the North Atlantic during the last Ice Age were actually global in extent," Cardiff University said of the study.

"It confirms predictions that abrupt climate change is global in nature," said Stephen Barker of Cardiff University, who was lead author of the paper in the journal Nature along with other experts in Britain and the United States.

"Were an abrupt climate change to come in the future we'd know a bit more about it," he told Reuters of the study that could point to the risks of future disruptions to Atlantic Ocean currents.

Gulf Stream

The report could help understand risks, for instance, of a slowdown of the Gulf Stream current that keeps northern Europe warm. Oslo, for example, is almost as far north as Anchorage in Alaska but is far warmer because of the Gulf Stream.

The U.N. Climate Panel said in a report in 2007 that it was "very unlikely" that the Gulf Stream and related Atlantic currents would collapse this century because of global warming. But it predicted the currents would slow.

Any breakdown of the Gulf Stream could bring a sharp cooling to northern Europe and a warming in the Southern Hemisphere.

Barker said the Gulf Stream carried warm waters north in what he called "heat piracy" from the south. A slowdown would mean more heat stayed in the Southern Hemisphere -- cooling the north and warming the south.

Under a northern cooling, areas of warm water would spread southwards with possible impacts ranging from disruptions to fisheries to the ocean's ability to soak up greenhouse gases, he said.

The U.N. Climate Panel says that a build-up of greenhouse gases, mainly from burning fossil fuels, may bring more heatwaves, floods, droughts and rising seas.

-- For Reuters latest environment blogs click on: blogs.reuters.com/environment/

Editing by Louise Ireland

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