Europe's relatively mild climate depends on a system of currents known as the North Atlantic heat conveyor.A CSIRO scientist, Stephen Rintoul, said it was premature to blame the weakening of the North Atlantic heat conveyor on global warming.
Warm surface waters from the tropics flow northwards in the Gulf Stream, releasing heat to the atmosphere, before sinking and returning southwards as a deep cold current. Global warming is forecast to disrupt this system by injecting fresh water into the Atlantic near the North Pole as rain increases and the Greenland ice cap melts. A slowdown in the heat conveyor could cause European temperatures to drop by 4 degrees.
In a study published today in the journal Nature, British researchers at the National Oceanographic Centre in Southampton surveyed the strength of currents at various depths in the subtropics.
They found the circulation system had weakened overall by 30 per cent since 1957, with a 50 per cent reduction in the amount of cold deep water flowing southwards and a 50 per cent increase in the amount of water that never leaves the subtropics. "The implications of these observations are considerable," Professor Quadfasel said. In the past, temperatures have dropped by up to 10 degrees in a decade. This happened after a huge amount of fresh water from melting ice sheets, which had been caught behind a natural dam, suddenly flooded the North Atlantic and shut down the heat conveyor about 8500 years ago.
If global warming caused a similar shutdown, this would have "devastating effects on socio-economic conditions in the countries bordering the eastern North Atlantic," Professor Quadfasel said.
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