快猫短视频

THE ocean currents that give Europe its mild climate are changing. 快猫短视频s have found evidence that global warming may cause a big freeze by switching off a current called the North Atlantic Drift.

Several teams have found signs that the current, which brings warm water to northwest Europe from the Gulf Stream, is being disrupted by a growing amount of freshwater entering the Arctic Ocean. This increase is a result of changes attributed to global warming: melting ice, increased rainfall and changing wind patterns.

The North Atlantic Drift is part of a global conveyor belt that brings warm surface water from the Gulf of Mexico to northwest Europe and sends cold deep water back. The belt is driven by two 鈥減umps鈥�, one in the Greenland Sea and one in the Labrador Sea, where the surface water cools, sinks and then returns south.

A computer model developed by Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany and his colleagues suggests that global warming could turn off the North Atlantic Drift, causing temperatures in northwest Europe to drop by 5 掳C or more (快猫短视频, 8 February 1997, p 26). However, there has been no evidence that this is really happening.

But now Bill Turrell, leader of the Ocean Climate Group at the Scottish Executive鈥檚 Marine Laboratory in Aberdeen, has found evidence that fits in with Rahmstorf鈥檚 predictions. He analysed more than 17 000 measurements of seawater salinity between Shetland and the Faroe Islands since 1893.

Turrell found that in each of the past two decades the salinity of the deep water flowing south has dropped by 0.01 grams of salt per kilogram of seawater. So its density has probably also decreased by 0.01 kilograms per cubic metre per decade. 鈥淭his is the largest change we have seen in the outflow in the last 100 years,鈥� says Turrell. 鈥淚t is consistent with models showing the stopping of the pump and the conveyor belt.鈥� In the 1950s the salinity of the outflow was so stable it was used to calibrate equipment.

His findings are echoed by work at the Fisheries Laboratory of the Faroes. Monitoring there suggests the deep water outflow through the channel southwest of the islands is getting warmer. In a study yet to be published, Bogi Hansen of the lab says the level at which water is at -0.5 掳C dropped by 60 metres between 1988 and 1997.

Svein 脴sterhus of the University of Bergen in Norway has also discovered that a deep-sea current closer to the Arctic has gone into reverse. In 1982 and 1983, deep water flowed southwards from the Greenland Sea into the Norwegian Sea at 10 centimetres per second. But in 1992 and 1993, the water was flowing at 1 centimetre per second in the opposite direction. This indicates that the Greenland Sea pump 鈥渉as been dramatically reduced in power鈥�, says 脴 sterhus.

鈥淎ny evidence that changes in ocean currents are starting to occur is very important,鈥� says Rahmstorf. 鈥淭he freshening and warming of the deep water flowing back into the Atlantic is consistent with global warming but could also have natural causes.鈥�