http://www.thestar.com/NASApp/cs/Conten ... 8793972154
Weaker ocean currents pose risk
Warm water not making it north
Dec. 1, 2005. 05:27 AM
PETER CALAMAI
SCIENCE REPORTER
MONTREAL—Scientists have detected a weakening of key water currents in the Atlantic Ocean, raising fears of major ecological upheavals, including colder winters in northeastern Canada and Europe.
These currents, which continually move warm and cold water around the Atlantic, have slowed by 30 per cent since 1992, a drop unequalled since the last Ice Age, British researchers reported yesterday in the journal Nature.
If the trend continues, experts forecast that changes to the so-called Atlantic conveyor belt could trigger major environmental disruptions, including not only colder winters in parts of Canada and Europe but severe declines in the North Atlantic fisheries, droughts in India and sea levels rising as much as a metre along the eastern seaboard of North America.
Computer projections show such catastrophic environmental effects would hit the Northern Hemisphere within two decades of any collapse of the Atlantic conveyor.
"The consequences would be global, not just regional," said Bill Hare, an expert in the field, who is attending the two-week United Nations climate change conference in Montreal.
His views were echoed by Gordon McBean, a former head of the Meteorological Service of Canada, who directs the federal funding agency for climate science.
"Although important for Europe's climate, this is also very important for global climate," McBean wrote in an email.
The Atlantic conveyor carries deep cold water from the Arctic down south to the equator and returns to the north warm water, which is close to the surface.
If the Atlantic Ocean is moving less heat northwards, then the atmosphere must take up the slack to keep the tropics-to-poles system balanced. McBean said the most likely way for this to happen would be an increase in violent storms in the area from the mid-United States to mid-Canada.
Climate change poses a threat to the Atlantic conveyor. Rising air temperatures melt polar ice, making water flowing out of the Arctic less salty, which is also less dense. This water then can't sink enough to flow back south.
Disruption of the Atlantic conveyor had been widely predicted.
A report from the U.S. defence department earlier this year noted the consequences of a slowdown in the Atlantic conveyor, saying that the climate of Britain and northern Europe would be more like Siberia's and the average rainfall would decline by 30 per cent.
But yesterday's report conducted by a research team from Britain's National Oceanography Centre found the first hard evidence for the change after comparing temperature and salinity readings from last year to four previous snapshots dating back to 1957 — all recorded by monitoring devices along a line from Morocco to Miami.
Measurements in 1981 and 1992 had shown little change from the readings of 1957.
But a major shift was revealed in readings from 1998 and last year, with less of the warming current getting up to Greenland and also less of the cold, deep returning current coming back.
Lead researcher Harry Bryden told a news conference yesterday in London that long-term monitoring was essential to learn whether the figures signalled a one-time readjustment or the start of a trend.
"It is like a radiator heating the atmosphere and is too important to leave to periodic observations," Bryden said.
Bryden's concern was echoed by Canadian climate and ocean experts.
"This says that the ocean circulation isn't rock-solid stable, but we still don't know how unstable it is," said Allyn Clark, a circulation expert at the Bedford Institute of Oceanography in Dartmouth.
Clark said a key question is whether the weakening of the conveyor was a trend that would continue.
Concerted research into the issue began only in the past two decades, he said.
"It takes a long time to do the observational studies and then do the modelling studies to answer these questions," Clark said.
British and American scientists are tackling the Atlantic conveyor questions by deploying semi-permanent monitoring devices along a line 25 degrees north of the equator, where the earlier temperature and salinity measurements were also taken.
The British research found evidence that much greater amounts of water are simply going around in a circle in this subtropical region and not completing the full circuit up to the Arctic and back.
As well, the monitoring program includes new seabed recording devices at three crucial locations off the coast of North America to directly measure the cold water flowing south from the Arctic, known as the deep western boundary currents.
News of the disruptions to the Atlantic conveyor spread quickly among participants at the U.N. climate change conference.
"This should provide added impetus to the negotiations," said Hare, who works at the Potsdam Institute for Climate Impact Research, an international research institute.
Conference president Stéphane Dion, the federal environment minister, said he was not aware of the research findings.
we are fucked
