The oldest ice can be thought of as a kind of glue that holds the Arctic together and, through its relative permanence, helps keep the Arctic cold even in long summers.

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“The younger the ice, the thinner the ice, the easier it is to go away,” said Don Perovich, a scientist at Dartmouth who coordinated the sea ice section of the yearly report.

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If the Arctic begins to experience entirely ice-free summers, scientists say, the planet will warm even more, as the dark ocean water absorbs large amounts of solar heating that used to be deflected by the cover of ice. The new findings were published as climate negotiators in Poland are trying to reach a global consensus on how to address climate change.

In March, NASA scientists with the Operation IceBridge mission, which surveys the polar regions using research aircraft, witnessed a dramatic instance of the ongoing changes. Flying over the seas north of Greenland, in a region that usually features some of the oldest, thickest ice in the Arctic, they instead saw smooth, thin strips binding together the thicker, ridged pieces.

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“I was just shocked by how different it was,” said NASA’s Nathan Kurtz, who has flown over the area multiple times. The floating sea ice had broken up entirely the previous month — very unusual for this location — and now was feebly freezing back together again.

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Scientists think a strange wind event caused the breakup in this region just a few hundred miles south of the North Pole — so it’s unclear whether it is directly linked to climate change. Still, the breakup could be just one more sign of the growing fragility of the oldest ice.

What matters is volume — not just ice area

The new findings about the decreasing age of ice in the Arctic point to a less noticed aspect of the dramatic changes occurring there. When it comes to the icy cap atop the Arctic Ocean, we tend to talk most often about its surface area — how much total ocean is covered by ice, rather than by open water. That’s easily visible — it can be glimpsed directly by satellite — and the area is, indeed, in clear decline.

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But the loss of old and thick ice, and the simultaneous decline in the total ice volume, is even larger — and arguably a much bigger deal. Young and thin ice can regrow relatively quickly once the dark and cold winter sets in. But it may not add much stability or permanence to the Arctic sea ice system if it just melts out again the next summer.

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The total volume of ice in September, the lowest ice month, declined by 78 percent between 1979 and 2012, the record low year. That’s according to an analysis by scientists at the University of Washington in Seattle called PIOMAS, or the Pan-Arctic Ice Ocean Modeling and Assimilation System — a top source for tracking ice volume.

In fairness, the ice volume has rebounded somewhat since 2012. And PIOMAS is only a model, cautioned the University of Washington’s Axel Schweiger, who runs the analysis. (The model draws upon direct measurements of ice thickness taken from submarines, satellites and other sources.) Still, Schweiger agreed that when you think about the total volume of the ice, rather than its mere surface extent, you realize that far more has been lost.

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“We’ve lost about half of the extent, we’ve lost half of the thickness, and if you multiply these two things, we’ve lost 75 percent of the September sea ice,” he said.

Going by PIOMAS’s numbers, the losses represent more than 10 trillion tons of ice. While the Arctic Ocean contained over 15 trillion tons of floating ice in 1979 during the month of September, in the same month in 2012, it averaged just under 3.5 trillion tons. This year, it averaged just 4.66 trillion tons in September.

“The Arctic is an indication of what’s coming to the rest of the globe,” said Walt Meier, a sea ice expert at the National Snow and Ice Data Center. “In the Arctic Ocean, a difference of 2 degrees can be huge. If it goes from 31 Fahrenheit to 33 Fahrenheit, you’re going from ice skating to swimming. … the Arctic is an early warning system for the climate.”

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The Arctic’s new youth

And the transition isn’t just about ice volume — it’s the Arctic’s version of the film “The Curious Case of Benjamin Button.” The ice is literally getting younger.

The oldest Arctic ice, having survived four summers or more and called “multiyear ice,” is the thickest. It has built up its mass over time and can be well over 10 feet thick. It can grow even thicker in places where it develops tall ridges from slamming into other pieces of ice, or from sustained pressure from the rest of the pack.

But this ice is either melting because of warming air and seas, or getting expelled southward through the Fram Strait, between Greenland and Svalbard — and then melting in warmer subarctic waters.

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Increasingly, what remains is ice that only forms after the peak warmth of the summer, usually in September, and which may not survive the following summer. This “first year ice” is more brittle, more easily tossed around by winds and waves, rendering the Arctic ice pack more mobile and prone to breaking apart.

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In 1985, the new NOAA report found, 16 percent of the Arctic was covered by the very oldest ice, more than four years old, at the height of winter. But by March, that number had dropped to under 1 percent. That’s a 95 percent decline.

At the same time, the youngest, first-year ice has gone from 55 percent of the pack in the 1980s to 77 percent, the report finds. (The remainder is ice that is two to three years old.)

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“A decade ago, there were vast regions of the Arctic that had ice that was several years old,” said Alek Petty, a NASA researcher who works with the Operation IceBridge project. “But now, that’s a rare phenomenon. … If you get rid of that ice that’s five or 10 years old, obviously it will take that long to replenish it."

“And it doesn’t look like that’s going to happen,” Petty said.

The deep danger of a dark Arctic Ocean

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This process of reverse-aging, scientists say, is all headed to a crucial moment — when all of the ice in the Arctic will be thin and a year old or less. When that happens — the day of maximum youth — we will be on the verge of a much feared milestone: an entirely ice-free Arctic Ocean in summer.

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“Looking down from the North Pole from above, for all intents and purposes, you’re going to see a blue Arctic Ocean,” Meier said.

It’s not clear how soon such an event could arrive. A recent report from the Intergovernmental Panel on Climate Change, for instance, suggested it would occur once every 10 years if the globe’s total warming reaches 2 degrees Celsius, but only once every 100 years at 1.5 degrees Celsius. (Warming is at 1 degree Celsius now.)

So by the time we cross 1.5 degrees, potentially within the next few decades if warming continues, the odds of a first ice-free summer will start rising.

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The reason Arctic ice is shrinking so fast, and why scientists are worried about it continuing, is one and the same.

There is a well-known feedback loop in the Arctic, caused by the reflectivity of ice and the darkness of the ocean. When the Arctic Ocean is covered by lighter, white ice, it reflects more sunlight back to space. But when there is less ice, more heat gets absorbed by the darker ocean — warming the planet further. That warmer ocean then inhibits the growth of future ice, which is why the process feeds upon itself.

The open ocean absorbs about twice as much sunlight as floating sea ice, explained Veerabhadran Ramanathan, a climate expert at the Scripps Institution of Oceanography who was the discoverer of the role of chlorofluorocarbons (or CFCs) in not only destroying the ozone layer but also amplifying global warming.

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Because of this, Arctic sea ice loss has already increased the warming of the planet as a whole. Ramanathan said the impact is equivalent to the warming effect of 250 billion tons of carbon dioxide emissions, or about six years of global emissions.

Ramanathan fears that entirely ice-free summers, if they began to occur regularly, could add another half- degree Celsius (0.9 degrees Fahrenheit) of warming on top of whatever else the planet has experienced by that time.

“If that were to happen, I would think of it as an unmitigated disaster,” said Ramanathan of consistently ice-free Arctic summers. “It will quickly pump in this half a degree warming.”

That extra warming, he said, in turn could trigger a world with multiple other cascading effects, such as increasing losses of carbon from northern permafrost soil, or major damage to the Amazon rain forest. The additional heat would also melt snow cover over land in the Arctic, further driving up global temperatures as the darker land surface absorbs more incoming radiation.

Some consider the Arctic situation so dire that it calls for an emergency intervention. A group called Ice911, founded by inventor and Stanford lecturer Leslie Fields, is proposing a strategic “geoengineering” project that would involve spreading reflective silica particles across young sea ice in key areas, to bounce back more sunlight and help the fledgling ice get through its first summer.

“If and when there is a decision to pursue an intervention in the Arctic, or somewhere else, we want to be out there with all of our field testing, climate modeling, and testing complete to say, here is a viable, safe solution for restoring ice that can mitigate some of these extreme impacts,” said Roman Decca, a strategist with the group.

We’re still far from a world in which such a radical step is under serious consideration. But the concern of Arctic researchers is hard to ignore.