An unusual pattern of winds has driven the old Arctic sea ice into a precarious position during the winter of 2020. Now, in warming waters, large areas of the shrinking supply of old Arctic ice are at risk of melting. But how did it happen and why is old ice so important?
When winter darkness falls over the Arctic Ocean, temperatures drop below -30 Â° C. The existing floating ice thickens as the underlying seawater freezes and the ice advances into areas that were previously open water. In summer, when temperatures rise and the sun shines for months, the ice thins and recedes. Each September, scientists expect and monitor the minimum annual Arctic sea ice cover – a useful indicator of how quickly the region is changing.
The ice that survives the summer melt season lasts another winter. Some ice cream even survives several summers before finally melting. This especially occurs in the cooler regions near the North Pole. Ice that survives summer is known as perennial ice; marked by the battle of its ordeal, it ends up being thicker, rougher and more resistant. It is an important part of the arctic climate and ecology and it is disappearing due to global warming.
When sunlight hits the Earth, it is either reflected or absorbed. The reflected light bounces in space, while the absorbed light warms the planet. Snow-covered sea ice reflects up to 90% of incoming sunlight, making it a powerful defense against global warming. But as the polar ice pack melts due to climate change, more and more sunlight is hitting the ocean, where more than 90% is absorbed.
Perennial ice is particularly important because it is more able to survive the summer and protect the Arctic Ocean from the sun and keep the region cool. But every year the ice melt season gets longer and the growing season gets shorter. And both seasons in the Arctic are getting warmer. These factors conspire against perennial ice, and fewer and fewer have survived the melt season each year.
Why was the winter of 2020-2021 so exceptional?
To maintain a healthy perennial ice cover in the Arctic, it is essential that the ice stays away from warm waters where it could melt in the summer. Sea ice moves around the Arctic Ocean when it is blown away by the wind. If it stays in cold regions, where ice can survive the summer, it has a good chance of becoming perennial ice. If winds blow him south into warmer waters, his chances of survival drop dramatically.
In February 2021, my university colleagues and I observed a surprising weather phenomenon in the Arctic. The polar vortex, a ring of counterclockwise wind that contains a puddle of extremely cold air over the arctic, has collapsed, setting a new air pressure record of highest surface in the region. The cold weather then moved south to the surface, causing temperatures in the UK to drop to their lowest level since 1995. In Texas, extremely cold weather crippled the power grid, leaving four million people without. electricity.
In the Arctic, the rupture of the polar vortex produced an exceptional pattern of surface winds that swirled clockwise around the center of the Arctic Ocean like water around a hole in the sea. emptying. These swirling winds made the floating ice floe spin like a top. In doing so, they chased perennial Arctic ice from a relatively safe and cold position north of Greenland to an area where ice increasingly cannot survive summer: the Beaufort Sea.
Over the winter, the Beaufort Sea filled with perennial ice such that during the last week of February 2021 it contained a record fraction (23.5%) of the total ice cover perennial of the Arctic Ocean. This is where things get really interesting.
Perennial ice is, in theory, resistant to melt in summer. It is thicker and is usually covered with a deeper protective layer of snow. By positioning robust ice in an area where ice generally melts, scientists could record greater ice cover than the September minimum. But it will come at the cost of the perennial ice cover itself which, while robust, is more precarious than ever in a region prone to melting.
This highlights the fact that there is no single barometer for the health of the Arctic sea ice. The September minimum cover is important (and high profile), but so is the thicker and more rugged perennial ice cover. These two measures will likely tell different stories in September.
So what does the future look like for old Arctic ice? As the region continues to warm to a level three times the global average, less and less of the ocean will be able to survive for ice in the summer.
Recent research using the latest generation of climate models predicts that at least September sea ice coverage will fall to conditions known to be âice freeâ around 2035. Since satellite recording began in 1984, coverage perennial ice has about half, and this downward trend will continue.
During the last week of February 2021, perennial ice cover was the second lowest on record, behind 2013. At the time of writing, using the most recent data, perennial ice cover has significantly decreased and is increasing. Now sits at record low – its precarious positioning since the winter has likely played a role. With more than a month of the melting season before the September low, there is still a lot to play. But it’s likely that 2021 will set a new record for the lowest perennial ice cover.