Low ice coverage comes despite cooler-than-normal arctic summer.

https://i.imgur.com/HCiiwmH.png

Mark it down, Arctic sea ice watchers: the US National Snow and Ice Data Center (NSIDC) has (preliminarily) called the annual minimum ice extent. On September 10, Arctic sea ice coverage dipped to 4.14 million square kilometers (1.6 million square miles) before ticking back upward for a few days. While it’s possible that a couple more days of shrinkage could come along, that was probably the low point for the year.

That puts 2016 in second place for the lowest minimum on record—statistically tied with 2007, which was within the error bars of this year's data. The record low is retained by 2012, which fell to an incredible 3.39 million square kilometers. This continues the trend of marked decline observed by satellites since 1979.

https://i.imgur.com/mtH0SUZ.png

The ice was a little harder to track than usual this time around. Earlier this year, the Defense Meteorological Satellite Program satellite used by the NSIDC to track Arctic sea ice went on the fritz. After careful calibration, they switched to the next satellite in the series, bringing daily updates back online a couple months later and ensuring that there was no gap in the record.

The year so far is seeing record warmth and, in March, the annual maximum Arctic sea ice extent dropped to a record low, prompting some to wonder if a new record minimum might be in the offing. Sea ice extent is more complicated than you might think, though, and summer weather plays a huge role in determining what we end up with in September.

This summer’s weather wasn’t particularly conducive to getting rid of sea ice, although ocean temperatures were pretty warm. In the first week and a half of September, shrinkage picked up speed after a pair of storm systems in the Beaufort and Chukchi Seas compacted broken-up ice. That caught 2016 up to 2007, but it wasn't enough to create a new record.

The NSIDC notes that at least the southern route of the Northwest Passage—hugging between Victoria Island and the Canadian mainland—has been open again.

At the other end of the world, Antarctic sea ice—which marches to the beat of a very different drum—has been below the satellite-era average as it approaches the time of its annual maximum.