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Greenlands melting glaciers have the power to change Britain. climate because of the way they can interfere with the Gulf Stream of the North Atlantic, which keeps winters relatively mild.

Scientists have found the first hard evidence to show that this actually happened 8,200 years ago, when the climate in parts of the northern hemisphere cooled dramatically after a period of global warming.

Paradoxically, a warmer world could lead to harsher winters in Britain because of the way that melting freshwater from the Greenland ice cap can interfere with the saltwater engine that drives the Gulf Stream.

The scientists found that 8,200 years ago the North Atlantic current slowed down at a time when a freshwater lake, which had formed from the melting glaciers of the last Ice Age, flooded into the sea.

They believe that the lake released so much freshwater it diluted the surface water of the sea and so slowed down the warm North Atlantic currents, which are generated by the sinking of cold, salty water.

The 8,200-year-old event is the most recent abrupt climate-change event and by far the most extreme cooling episode in the past 10,000 years,? Mark Chapman, a palaeoclimatologist at the University of East Anglia in Norwich, said.

The study, published in the journal Science, involved drilling for a core of seabed sediments from the south of Iceland and analyzing it for indications of both the speed of the ocean currents and the saltiness of the sea.

Our records show a sequenced pattern of freshening and cooling of the North Atlantic sea surface and a change in the deep ocean circulation, all key factors ¦ in controlling¦ northern hemisphere climate, Dr Chapman said.

The core contained sediments representing the current interglacial warm period that began at the end of the last Ice Age about 10,000 years ago, Christopher Ellison of the University of East Anglia said.

â??The sediment includes¦ small animals called foraminifera that record surface water conditions in their shells when living, Mr Ellison said. We also analyzed the sediment grain size to gauge the speed of ocean currents and the strength of ocean circulation.

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According to Paul R. Epstein, at the Center for Health and the Global Environment at Harvard Medical School. Global Warming is whats making it colder in the winter in the US:
Normally, water circulates in the North Atlantic like this: Cold, salty water at the top sinks; that sinking water acts as a pump, pulling warm Gulf Stream water north and thus moderating winter weather. But now, fresh water from the thawing ice and heavier rain is accumulating near the oceans surface; its not sinking as quickly. (The tropics are faced with the opposite phenomenon.)

According to Dr. Ruth Curry and her colleagues at the Woods Hole Oceanographic Institution, the tropical Atlantic is becoming saltier; as warming increases, so does evaporation, which leaves behind salt.) The freshening? in the North Atlantic may be contributing to a high-pressure system that is accelerating trans-Atlantic winds and deflecting the jet stream changes that may be driving frigid fronts down the Eastern Seaboard. The ice-core records demonstrate that the North Atlantic can freshen to a point where the deep-water pump fails, warm water stops coming north, and the northern ocean suddenly freezes, as it did in the last Ice Age.

No one can say if that is what will happen next. But since the 1950, the best documented deep-water pump, between Iceland and Scotland, has slowed 20 percent?

Lyn Rose

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