Where’s the sea ice? 3 reasons the Arctic freeze is unseasonably late and why it matters

<span class="caption">Arctic sea ice levels have been falling for several decades.</span> <span class="attribution"><a class="link rapid-noclick-resp" href="https://www.gettyimages.com/detail/news-photo/vintage-map-of-robert-pearys-1909-north-pole-expedition-news-photo/525373411" rel="nofollow noopener" target="_blank" data-ylk="slk:GraphicaArtis/Getty Images">GraphicaArtis/Getty Images</a></span>
Arctic sea ice levels have been falling for several decades. GraphicaArtis/Getty Images

With the setting of the sun and the onset of polar darkness, the Arctic Ocean would normally be crusted with sea ice along the Siberian coast by now. But this year, the water is still open.

I’ve watched the region’s transformations since the 1980s as an Arctic climate scientist and, since 2008, as director of the National Snow and Ice Data Center. I can tell you, this is not normal. There’s so much more heat in the ocean now than there used to be that the pattern of autumn ice growth has been completely disrupted.

To understand what’s happening to the sea ice this year and why it’s a problem, let’s look back at the summer and into the Arctic Ocean itself.

Siberia’s 100-degree summer

The summer melt season in the Arctic started early. A Siberian heat wave in June pushed air temperatures over 100 degrees Fahrenheit at Verkhoyansk, Russia, for the first time on record, and unusual heat extended over much of the Arctic for weeks.

The Arctic as a whole this past summer was at its warmest since at least 1979, when satellite measurements started providing data allowing for full coverage of the Arctic.

With that heat, large areas of sea ice melted out early, and that melting launched a feedback process: The loss of reflective sea ice exposed dark open ocean, which readily absorbs the sun’s heat, promoting even more ice melt.

The Northern Sea Route, along the Russian coast, was essentially free of ice by the middle of July. That may be a dream for shipping interests, but it’s bad news for the rest of the planet.

Warmth sneaks in underwater

The warm summer is only part of the explanation for this year’s unusual sea ice levels.

Streams of warmer water from the Atlantic Ocean flow into the Arctic at the Barents Sea. This warmer, saltier Atlantic water is usually fairly deep under the more buoyant Arctic water at the surface. Lately, however, the Atlantic water has been creeping up. That heat in the Atlantic water is helping to keep ice from forming and melting existing sea ice from below.

It’s a process called “Atlantification”. The ice is now getting hit both from the top by a warming atmosphere and at the bottom by a warming ocean. It’s a real double whammy.

While we’re still trying to catch up with all of the processes leading to Atlantification, it’s here and it’s likely to get stronger.

Climate change’s assault on sea ice

In the background of all of this is global climate change.

The Arctic sea ice extent and thickness have been dropping for decades as global temperatures rise. This year, when the ice reached its minimum extent in September, it was the second lowest on record, just behind that of 2012.

As the Arctic loses ice and the ocean absorbs more solar radiation, global warming is amplified. That can affect ocean circulation,

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