Thinning ice in the Arctic Ocean made this year’s navigation season for natural gas tankers the longest on record, the latest sign that the pace of climate change is accelerating in the Earth’s northernmost latitudes.

The Northern Sea Route, stretching more than 3,000 nautical miles between the Barents Sea west of Russia and the Bering Strait in the country’s east, traditionally opens from June through October, when higher temperatures break up ice. This year, voyages started a month early and will continue until at least the end of December. Record warmth meant slower freezing during the autumn.

"This year could potentially become a turning point for the Arctic,” said Samantha Burgess, deputy director at Europe’s Copernicus Climate Change Service. "This was a fairly exceptional year in that the warmer-than-average condition was incredibly persistent throughout the whole year.”