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Arctic melt opens Northwest passage

Record low for sea-ice retreat.

The most direct shipping route between the Atlantic and Pacific oceans, connecting Asia and Europe, is fully navigable for the first time since records began, data show. Warming has led to a record retreat of Arctic sea ice, which covers about 16 million square kilometres during March each year and melts to a minimum sometime in September or October. The previous record minimum was 5.32 million square kilometres, set in 2005, but this year it has already reached a low of 4.24 million square kilometres, according to the US National Snow and Ice Data Center in Boulder, Colorado.

The drop may have been caused by warmer ocean waters over the past few summers, says John Walsh, a climate scientist at the University of Illinois in Urbana-Champaign. This summer has been unusually cloud-free, and spring temperatures over the Russian part of the Arctic were higher than usual, he says. Lack of sea ice itself contributes to warming, since ice reflects the Sun's heat better than the sea. The Intergovernmental Panel on Climate Change predicts that if current trends continue, a summer without sea ice will occur in the next 40 to 100 years.

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Cressey, D. Arctic melt opens Northwest passage. Nature 449, 267 (2007). https://doi.org/10.1038/449267b

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