Antarctic Sea Ice Is at Record Lows. Is It an Alarming Shift?
Even more astonishing is that records of Antarctic sea ice did not occur until the mid-2010s heights– at least the highest values since satellite observations began – which have increased slightly but steadily in the years since 1979.
Recent growth in Antarctic sea ice stands in stark contrast to 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 continuously for decades. This is due to a phenomenon called Arctic Amplification: melting ice exposes darker seawater or land that absorbs more solar energy than white ice, which in turn leads to more 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. The ice of Antarctica is somewhat insulated by strong, cold ocean currents that swirl around the continent. In addition, Antarctica is quite high, which provides additional cooling.
Antarctica’s sea ice, which forms when seawater freezes, differs from the continent’s ice sheets and shelves. There is an ice sheet on the land that can be several thousand meters thick. It becomes an ice shelf when it begins to float on coastal waters. While Antarctica’s ice sheets and shelves have indeed deteriorated as the planet has warmed, the continent’s sea ice is much more seasonal, increasing and decreasing dramatically between winter and summer.
Losing sea ice does not cause sea levels to rise any more than melting ice cubes floating in a glass of water do not cause the glass to overflow. (The ice is already displacing the water.) However, sea ice plays a crucial role in protecting Antarctica’s vast ice shelves from decay, and these could cause sea levels to rise dramatically if they break apart. If fully melted, Thwaites Glacier, also known as Doomsday Glacier, could raise sea levels by 10 feet. Sea ice protects Thwaites and other glaciers because it acts as a buffer, absorbing the energy from winds and waves that would otherwise erode them. It also cools the air flowing over coastal waters, preventing the ice shelves from melting.
This year the coast of West Antarctica was particularly ice-free. “It’s the area where climate researchers are most concerned about possible massive contributions from the ice sheet to global sea level rise,” says Maksym. “This year we’re not seeing any sea ice in this area at all, which I think is pretty much the first time something like this has happened.” Then there are a few earlier ones studies This has shown that when you remove sea ice, the type of support is lost, and that can accelerate ice shelf breakup.”
But that’s not the only global impact the loss of sea ice will have: When seawater freezes into ice, the denser brine that’s left sinks to the seafloor, creating deep currents that rush away from Antarctica. The less sea ice, the weaker these currents are. “This will affect the efficiency with which the oceans allocate energy and ultimately the global climate,” says UCLA geographer Marilyn Raphael, who studies the region. “What happens in Antarctica doesn’t stay in Antarctica.”