Observations measured last week showed sea ice surrounding Antarctica at its lowest levels in the 44 years since such measurements began.
Map of the smallest ever sea ice extent ever recorded for Antarctica. Based on satellite data captured on February 21, 2023. Image: National Snow and Ice Data Center/NASA Earth Observatory
Just as in the Arctic, the ebb and flow of sea ice as the seasons shift are regularly tracked by scientists in the Antarctic.
In the Arctic, the metrics provide a clue to how global heating from the climate crisis is accelerating and sea level rise continues its steady upwards trajectory.
In the Antarctic, the same is true but scientists are also looking for data which could point to a far more sudden separation of any of the massive ice sheets along its 18,000 km (11,200 mile) coastline. If that happens, many square kilometers of ice could suddenly float away from the pole and into warmer waters northwards, with melting causing average sea levels to rise by a foot or more, flooding coastlines and major cities from Miami to Manila in the Philippines, to Shanghai in China, and Kolkata, India, all at once.
The data on Antarctic ice received last week does not include that catastrophic breakoff of ice yet. But it is the lowest amount of ice ever recorded for this time of the year, as autumn in the South Pole approaches and temperatures begin to fall so some refreezing can begin.
The typical ice cycle for the continent has in the past averaged roughly 18 million square kilometers (7 million square miles) at peak every September. After summer melting, the ice coverage falls to just 2 million square kilometers (0.78 square miles).
That cycle was shattered last year, when on February 25, 2022, the maximum Antarctic sea ice extent dropped to a record low coverage of 1.92 million square kilometers (0.74 square miles).
This year that record was broken again. As of February 12, 2023, when the latest satellite data was taken, the total ice coverage in Antarctica had dropped to just 1.79 square kilometers (0.69 square miles). That level, now the lowest recorded since 1979, represents a 6.8% decline in just one year.
That 136,000 square kilometers drop in the minimum ice coverage is only slightly larger than the country of Greece, which has a land mass of 132,000 square kilometers.
2023 also represents the third time that record record has been broken in the last six years.
Dr. Will Hobbs, a member of the Australian Antarctic Program Partnership and an expert of that continent’s sea ice at the University of Tasmania, is one of those who watched as the sea ice there fell further and more rapidly than ever surrounding the South Pole this year.
“By the end of January, we could tell it was only a matter of time,” he said in an interview about these developments recently.
“We are seeing less ice everywhere,” he continued. “It’s a circumpolar event.”
The lack of ice this season was not the only area of concern for Hobbs’ team. They had already observed that after last year’s decline the ice had only refrozen at all late into the local winter season last year.
At least part of that delay was caused by an unusual atmospheric heat wave which built up over the continent in March 2022. That raised temperatures as much as 18° to 20° F over normal.
Hobbs also pointed to the more recent discoveries as to why the Antarctic ice is melting so rapidly. It is no longer the direct energy of the sun that is the primary cause. It is instead from secondary effects.
“Because sea ice is so reflective, it’s hard to melt from sunlight,” he’ said. “But if you get open water behind it, that can melt the ice from underneath.”
That is supported by numerous recent studies. In a pivotal one published in October 2019, an international team documented how the floating ice shelves of Antarctica were being pummeled by often fast-moving warm water “rivers” submerged below the ice. Follow-up experiments using submarine drones, plus specialized sonar and laser monitoring equipment, illustrated more accurately how fast the sea ice thickness was being diminished from underneath. As undersea melting continues, the fragility of the ice sheets surrounding Antarctica becomes a even bigger concern for researchers.
Cornell University's underwater drone Icefin robotic oceanographic observatory, shown here underneath an ice sheet such as it has been exploring in the Antarctic. Photo: Cornell University, Via Press Release
As the record low ice coverage has drawn many to study its potential impacts, the Thwaites Glacier in Antarctica, covering an area the size of Florida, is drawing much attention. It is the biggest ice flow in Antarctica which also is under high risk of fracturing, with an expanse 120 kilometers (76 miles) at its widest extent. If it were to break off and melt in its entirety, it could produce a 3-meter (9.8 foot) sea level rise all on its own. It is that sudden global flooding which has given the Thwaites its nickname, the “Doomsday Glacier”.
Scientists studying the glacier point out that while the Thwaites Glacier still remains intact, in its case warm water is doing far more than just swirling underneath its icy mass. A just-published study by scientists at the British Antarctic Survey revealed warm waters are seeping far upwards from the bottom of that ice, and forming “water canyons” now etching into the ice at a rate of 43 meters (141 feet) every year.
Researchers also have discovered that the ocean floor which used to support the bottom of some of the Thwaites Glacier is receding faster than anyone had known. It has pulled downwards and away by a net 14 kilometers (roughly nine miles) just in the last thirty years. That in turn has exposed far more of the Thwaites underbelly to the warm waters already sawing away at other parts of it.
Further, as the ice sheets grow thinner, they have less structural strength as storms and waves push them. This is further exacerbated by the overall drop in size of the Antarctic ice at its smallest, which then lays bare more of that ice to ordinary ocean currents rather than ones protected from below.
According to Dr Rob Massom of the Australian Antarctic mission, last month roughly 67% of all ice was exposed directly to normal ocean currents, up from the typical value of about half.
Further, as he pointed out recently, “It’s not just the extent of the ice, but also the duration of the coverage.”
“If the sea ice is removed, you expose floating ice margins to waves that can flex them and increase the probability of those ice shelves calving,” he explained. That then allows more grounded ice into the ocean.”
All this suggests a more rapid weakening ahead for the principal glaciers in the Antarctic, in addition to the dramatic overall drop in sea ice extent this year. Researchers will continue to monitor all, but it seems clearer than ever that the melting of Antarctica is accelerating and will continue to do so. While it may take some years more for large glaciers to break up and slide into the ocean, it is inevitable. Combined with the melting in the Arctic, ocean level rise will speed up and this means more coastal communities under water, loss of more cropland and vast numbers of climate refugees.
 “Troughs developed in ice-stream shear margins precondition ice shelves for ocean-driven breakup,” by Karen E. Alley, et. al., published in the 9 October 2019 issue of Science Advances.