Jet stream ‘to blame for record ice melt’

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IT has already been blamed for getting stuck in the wrong place and causing last year’s miserable summer.

But now experts at Sheffield University say changes in the jet stream were also responsible for “exceptional” melting of the second largest ice body in the world.

The Greenland ice sheet, a vast ice body covering roughly 80 per cent of the country, has experienced increased melting in the last 30 years.

More than 90 per cent of the ice-sheet’s surface melted on just one day, July 11, 2012, far exceeding previous records.

An international team led by Professor Edward Hanna, from the University’s Department of Geography, has concluded ocean temperatures and Arctic sea-ice cover were “relatively unimportant” factors in the record melt.

Research published in the International Journal of Climatology says it was mainly caused by “highly unusual” atmospheric circulation and changes in the jet stream – the narrow band of very strong air currents which encircle the globe several miles above the earth.

The scientists used computer model simulations and analysed data largely gathered by the Danish Meteorological Institute and US programmes.

Prof Hanna said: “Our research found that a ‘heat dome’ of warm southerly winds over the ice sheet led to widespread surface melting.

“These jet stream changes over Greenland do not seem to be well captured in the latest Intergovernmental Panel on Climate Change computer model predictions of climate change, and this may indicate a deficiency in these models.

“According to our current understanding, the unusual atmospheric circulation and consequent warm conditions of summer 2012 do not appear to be climatically representative of future ‘average’ summers predicted later this century.”

It would take another decade to see whether 2012 was a rare event down to natural variability or part of an emerging pattern, he said.