A low ice extent at the peak of winter is troubling because from here on out, the ice will continue to shrink all the way into September, exposing ever more of the Arctic ocean to the sun’s warming rays and storing up heat in the system.

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The peak Arctic sea ice extent this winter is considerably lower than it was in 2015 or 2016, both of which were also extremely low years and vied for the prior record. Extent peaked at 14.517 million square kilometers in 2015 and 14.521 million square kilometers in 2016, according to data from the National Snow and Ice Data Center. Thus, the maximum extent this year was about 100,000 square kilometers less than in those prior years, or 38,600 square miles. That’s about the size of Indiana.

And this is part of a trend, notes NASA, which funds the National Snow and Ice Data Center and also hailed the record. “The Arctic’s sea ice maximum extent has dropped by an average of 2.8 percent per decade since 1979,” the agency noted.

Extremely low ice at this time of year may partly reflect the fact that over the course of the winter of 2016-2017, the Arctic region was buffeted by very strange weather. “Overall warm conditions were punctuated by a series of extreme heat waves over the Arctic Ocean,” the center reports.

The month of February in the Arctic, the most recent full month, also showed record low sea ice extent:

On top of all of that, the overall thickness or volume of Arctic sea ice is also at a record low right now, according to researchers at the Polar Science Center at the University of Washington in Seattle, and this is possibly an even more important observation. If the ice emerges from winter in a particularly thin state, then it has less of a chance of staying frozen throughout the remainder of the year as temperatures rise.

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The loss of this “multiyear ice” in the Arctic — ice that lasts in a frozen state for more than a year — is one factor that’s probably driving the decline of Arctic sea ice overall.

A lessening of the overall amount of ice covering the Arctic ocean weakens its core role in the broader climate system, which is to reflect sunlight away from the Earth. The less solar energy bouncing back to space, the more will remain to seep into the Arctic ocean, preventing the regrowth of ice later (a classic feedback in the climate system) and helping to melt seafront glaciers in Greenland and the Canadian and Alaskan Arctic.

It isn’t just the Arctic, either. From pole to pole, floating sea ice has been at extremely low levels in recent months. In the Antarctic summer, it recently plunged to a record low, also based on National Snow and Ice Data Center satellite data sets dating to 1979.

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But overall, Antarctic ice has shown a far more unpredictable pattern than has ice in the Arctic, bouncing around significantly in recent years and actually trending upward slightly overall — a behavior that has puzzled scientists. In contrast, the overall sea ice trend in the Arctic is an unmistakable downward trajectory, raising fears that it won’t be too long until we encounter an entirely ice-free Arctic in the summer.