NASA

Summer is officially done. In the Arctic, that means sea ice can once again take over, but not before falling to a near record low.

On Tuesday, the National Snow and Ice Data Center released data showing that on September 11, Arctic sea ice likely reached its annual low. Measuring in at 1.70 million square miles, it marks the fourth lowest extent since satellite measurements began in 1979.

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The reading is about 240,000 square miles lower than last year's low point and around 400,000 square miles above the all-time low of 1.3 million square miles set in 2012.

As Ted Scambos, who heads the National Snow and Ice Data Center (NSIDC) team science team, told the Washington Post, the really extraordinary thing about the degree of melt this year was that it wasn't a particularly extraordinary year otherwise.

“It’s showing us that the Arctic is truly evolving from a different state, and far from recovering, even relatively typical summers in the Arctic lead to relatively low sea ice extents,” he said.

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While the Arctic summer may not have been exceptionally notable, planet-wide 2015 is on track to be the hottest year ever, and August was the second hottest August on record. NASA recently released data showing that the summer of 2015 was the hottest on record—a full 1.4 degrees warmer than the long-term average.

The development of El Nino weather conditions in the Pacific Ocean have made temperatures hotter in the lower latitudes than in the northern reaches, such as the Arctic, according to Julienne Stroeve at the NSIDC.

This image shows a view of the Arctic on September 11, 2015 when sea ice extent was at 4.41 million square kilometers (1.70 million square miles). The orange line shows the 1981 to 2010 average extent for that day. The black cross indicates the geographic North Pole.

Overall, climate change is warming polar regions faster than other parts of the planet, and Arctic sea ice has been on a long-term decline since measurements began. The ten lowest measurements since 1979 have all occurred in the last 11 years. This year's readings reinforce this conclusion.

Not only has average summer minimum sea ice shrunk by 38% since records started 36 years ago, but the date of the lowest measurement has also been pushed forward. This year the 1.70 million square mile reading came on September 11, four days earlier than the 1981 to 2010 average minimum date of September 15.

In the long run, less Arctic ice cover means less resiliency for the ice that doesn't melt, according to Walt Meier, a sea ice scientist with NASA's Goddard Space Flight Center

"The sea ice cap, which used to be a solid sheet of ice, now is fragmented into smaller floes that are more exposed to warm ocean waters," he said in a statement. "In the past, Arctic sea ice was like a fortress. The ocean could only attack it from the sides. Now it's like the invaders have tunneled in from underneath and the ice pack melts from within."

The Northwest Passage of the Arctic as seen on Aug. 31, 2015.
NASA

Researchers said it's still possible that sea ice could diminish further this year if winds change or there's a surprise late-season melt in the next few days. Otherwise sea ice will begin growing, increasing in size through the winter and peaking in March.