Fossilised midges give climate clue
Updated on 15 July 2007
Midges that swarmed over British wetlands thousands of years ago old have sent a warning signal to climate scientists.
The fossilised insects bear witness to two periods of sudden climate change caused by disruption of the Gulf Stream. During each shift, one 9,000 and the other 8,000 years ago, average summer temperatures plunged 1.6C.
One cold period lasted up to 50 years and the other 150. The evidence suggests that Britain's climate is less stable than was previously thought and similar cold snaps could occur again, despite global warming.
Britain is kept warmer and wetter than it should be by the Gulf Stream, which brings heated water from the Atlantic close to its shores. Without it, Britain would have a climate similar to that of Labrador in Canada.
Some experts have suggested that the melting of polar ice caps caused by global warming might slow down or even halt the "Atlantic conveyor" ocean current which generates the Gulf Stream. Others do not believe the risk is serious enough to be of concern.
The midges indicate to scientists that such an event has already occurred twice - and relatively recently.
Researchers from the University of Liverpool collected fossilised midge heads from a site at Hawes Water, northern Lancashire, where consecutive layers of mud have been deposited without a break for thousands of years.
The number and type of midges in each sediment sample provided clues about what the climate was like at the time they were alive.
The findings were backed up by analysis of isotopes, different atomic forms of the same element.
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