A NOAA animation shows a startling loss of year-round ice in the mid-2000s.

Though the Arctic is easy to conceptualize as one big frosty sheet, it's in fact quite dynamic. Some of its ice is thick and old, the product of long-term glacial temperatures, and some is thinner and new, crystallizing each year in the cold season.

Recently, scientists have noted a drastic deterioration in the region's old or "multiyear" ice. Decades ago, the Arctic boasted a layer of year-round ice as deep as 23 feet; in just the past several years, however, this aged stuff has become "extremely rare," according to scientists at NOAA. To hammer home how rapidly the ice is melting, they've made this animation of frozen conditions from 1987 to 2014. Multiyear ice is depicted in white; notice how it pulls a major vanishing act in the mid-2000s.

NOAA lays out the anatomy of the loss:

East of Greenland, the Fram Strait is an exit ramp for ice out of the Arctic Ocean. Ice loss through the Fram Strait used to be offset by ice growth in the Beaufort Gyre, northeast of Alaska. There, perennial ice could persist for years, drifting around and around the basin’s large, looping current.

Around the start of the 21st century, however, the Beaufort Gyre became less friendly to perennial ice. Warmer waters made it less likely that ice would survive its passage through the southernmost part of the gyre. Starting around 2008, the very oldest ice shrank to a narrow band along the Canadian Arctic Archipelago.

Nearly a quarter of the Arctic's ice in the 1980s lasted year-round. Today, multiyear ice accounts for a mere 10 percent of the frozen mass. Why does this matter? For one thing, the thicker ice is a key component in the Arctic's health. "[P]erennial ice is more likely to survive the summer melt season," write scientists in Geophysical Research Letters. "Changes in perennial ice are therefore crucial to the mass balance of Arctic sea ice."

The deterioration in older ice is also a sign of the immense positive feedback happening around the North Pole. Warmer temperatures (such as those that made 2014 the hottest year in known history) create a smaller ice extent, allowing more of the ocean's surface to absorb heat, leading to even more drastic melting in the future. And ice reflects the sun's heat back into space; having less of it in Arctic, both old and new, will likely contribute to the planet's overall warming.

Some scientists believe that at the rate the Arctic is heating up, it will be virtually ice-free in summertimes before 2050. Here's a non-animated illustration of the Big Thaw from NASA, showing older ice as white in the winter of 1978...

...and in the winter of 2011:

NASA

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