Friday, April 12, 2024

Antarctic sea ice is at a record low. Is this a dangerous change?


Even more surprising, it was only in the Antarctic sea ice record in the mid-2010s. take off— at least as high as satellite observations began — has increased slightly but steadily in the years since 1979.

The recent increase of Antarctic sea ice stands in stark contrast to the Arctic, a region that is now warming four times faster than the rest of the planet and has been losing ice steadily for decades. This is due to a phenomenon called Arctic amplification: Melting ice exposes deep ocean water or land, which absorbs more of the sun’s energy than white ice, leading to more warming.

The Antarctic is a different animal: 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 in a sense insulated from the strong, cold ocean currents that circulate around the continent. Plus, Antarctica’s altitude is quite high, which provides additional cooling.

Antarctica’s sea ice—which forms when seawater freezes—is separate from the continent’s ice sheets and shelves. An ice sheet rests on the ground, and can be thousands of feet thick. When it starts floating on the coastal waters it becomes an ice shelf. While Antarctica’s ice sheets and shelves are indeed deteriorating as the planet warms, the continent’s sea ice is much more seasonal, increasing and decreasing dramatically between winter and summer.

Losing that sea ice would not cause sea level to rise, just as melting chunks of ice floating in a glass of water would not cause the glass to overflow. (The ice is already displacing water.) But sea ice plays a key role in keeping Antarctica’s vast ice shelves from deteriorating, and could dramatically raise sea levels if they break away . If it melts completely, Thwaites Glacier, aka Doomsday Glacier, could add 10 feet to sea level. Sea ice protects Thwaites and other glaciers because it acts like a buffer, absorbing the energy of winds and waves that would otherwise destroy them. It also cools air passing over coastal waters, which can prevent ice shelves from melting.

This year, the coast of West Antarctica has been notably devoid of sea ice. “This is the area where climate scientists are most concerned about the potentially large contribution to global sea level rise from the ice sheet,” says Maxim. “This year, we see no sea ice at all in that area, which I think is the first time it’s happened. Then there’s some former studies This suggests that if you remove sea ice, you lose a strengthening effect of sorts, and this could accelerate ice shelf breakup.

But that’s not the only global effect sea ice loss will have: When seawater freezes into ice, the denser brine left behind sinks to the ocean floor, creating deep currents that run away from Antarctica. The less sea ice, the weaker the currents. “This will affect the efficiency with which the oceans will deliver energy, and ultimately affect global climate,” says geographer Marilyn Raphael at UCLA. “What happens in Antarctica doesn’t stay in Antarctica.”