Antarctic sea ice is at record lows. Is it an alarming change?

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Even more surprising, it was only in the mid-2010s that Antarctic sea ice reached a record high. highs— at least maximums since satellite observations began — having risen slightly but steadily in the years since 1979.

That recent growth in Antarctic sea ice has contrasted with that of the Arctic, a region that is now warming. up to four times faster than the rest of the planet and has been losing ice steadily for decades. That is due to a phenomenon. called arctic amplification: Melting ice exposes darker ocean water or land, which absorbs more solar energy than white ice, which in turn leads to further warming.

Antarctica is a different beast: it’s a frozen continent surrounded by open ocean, while the Arctic is an ocean of floating ice surrounded by land, like Russia, Alaska, and northern Canada. Antarctica’s ice is insulated, in a sense, by strong cold ocean currents that swirl around the continent. Also, the elevation of Antarctica is quite high, which provides additional cooling.

Antarctic sea ice, which forms when seawater freezes, is distinct from the continent’s ice sheets and shelves. An ice sheet rests on the land and can be thousands of feet thick. It becomes an ice shelf when it begins to float in coastal waters. Although the Antarctic ice sheets and shelves have indeed been deteriorating as the planet warmsthe continent’s sea ice is much more seasonal, rising and falling dramatically between winter and summer.

Losing that sea ice won’t raise sea levels, just like melting ice cubes floating in a glass of water won’t make the glass overflow. (The ice is already displacing the water.) But sea ice plays a critical role in protecting Antarctica’s colossal ice shelves from decay, and could dramatically raise ocean levels if they break up. If it melts completelyThwaites Glacier, also known as the Doomsday Glacier, you could add 10 feet to sea level. Sea ice protects Thwaites and other glaciers because it acts as a buffer, absorbing energy from winds and waves that would otherwise erode them. It also cools the air passing over coastal waters, further preventing melting of the ice shelves.

This year, the West Antarctic coast has been particularly devoid of sea ice. “It’s the area where climate scientists are most concerned about potential massive ice sheet contributions to global sea level rise,” says Maksym. “This year, we’re seeing absolutely no sea ice in that area, which I think is pretty much the first time it’s happened. Then there are some earlier studies That showed that if you remove the sea ice, you lose the kind of reinforcing effects, and that can speed up the breakup of the ice shelf.”

But that’s not the only global effect the loss of sea ice will have: When seawater freezes into ice, the denser brine left behind sinks to the seafloor, creating deep currents that move away from Antarctica. The less sea ice, the weaker those currents. “This will affect the efficiency with which the oceans will distribute energy and ultimately affect global climate,” says UCLA geographer Marilyn Raphael, who studies the region. “What happens in Antarctica does not stay in Antarctica.”