The oldest and thickest sea ice in the Arctic has started to break up, opening waters north of Greenland that are normally frozen, even in summer.

This phenomenon – which has never been recorded before – has occurred twice this year due to warm winds and a climate-change driven heatwave in the northern hemisphere.

One meteorologist described the loss of ice as “scary”. Others said it could force scientists to revise their theories about which part of the Arctic will withstand warming the longest.

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