Arctic Sea ice melted this summer to its second lowest level since records began more than 50 years ago, mostly due to global warming, scientists have reported.
The US National Snow and Ice Data Centre reported that the amount of ice covering the Arctic hit its lowest point late last week, covering just 1.67 million square miles.
Only in 2007 was there less summer sea ice, which has been dramatically declining since scientists began using satellites to monitor the melting in 1979. Other records go back to 1953.
James Overland, of the US National Oceanic and Atmospheric Administration, said: "This is not a random event. It's a long-term change in Arctic climate."
Each summer, sea ice melts and then re-freezes, starting in the autumn. The summer minimum is a key measurement for scientists monitoring man-made global warming.
This year's level is 36% below the average minimum of 2.59 million square miles.
The University of Bremen in Germany, which uses a different satellite sensor and has been monitoring levels since 2003, reported last week that this year's sea ice actually fell below the record set in 2007.
Ice Data Centre research scientist Julienne Stroeve said two factors cause summer sea ice to shrink more than normal: man-made global warming and localised and seasonal Arctic weather.
In 2007, local weather conditions - wind, barometric pressure and sea currents - were all the worst possible for keeping sea ice frozen, she said, but this year, those seasonal conditions were not too bad. Nevertheless, the data centre's measurements show one of the worst years for melt.
Using computer models, scientists have predicted the Arctic will eventually be free of sea ice in the summer by the middle of the century, but a few researchers say it could happen as early as 2015 or 2020.
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