Named the danger of melting sea ice in Antarctica

For 44 years, satellites have helped scientists keep track of how much ice is floating in the ocean around Antarctica’s 18,000-kilometer coastline. Every year, massive shifts occur in the coastal waters of the continent: in September, the sea ice extent reaches a maximum of about 18 million square meters. km, and by February drops to just over 2 million square meters. km.

But in all these four decades of satellite observations, there has never been less ice on the continent than was recorded last week.

“By the end of January, we could say that it was only a matter of time. It didn’t even come close,” says Dr. Will Hobbs, an Antarctic sea ice expert at the University of Tasmania in partnership with the Australian Antarctic Program. “We see less ice everywhere. This is a circumpolar event.”

In the summer of 2022, in the southern hemisphere, the amount of sea ice on February 25 decreased to 1.92 million square meters. km, a record low based on satellite observations that began in 1979.

But by February 12 of this year, the 2022 record had already been broken. The ice continued to melt, hitting a new record low of 1.79 million square feet on February 25. km and breaking the previous record by 136,000 sq. km – an area twice the area of ​​\u200b\u200bthe island of Tasmania.

In the spring in the southern hemisphere, strong winds over western Antarctica ruffled the ice. At the same time, Hobbs says that vast areas in the west of the continent have barely recovered from the losses of the previous year.

“Because sea ice is so reflective, it is difficult to melt it from sunlight. But if there is open water behind it, it can melt the ice from below, ”says Dr. Hobbs.

Hobbs and other scientists said the new record – the third time it has been broken in six years – has started a fight for answers among polar scientists.

The fate of Antarctica – especially the ice on land – is important because the continent contains enough ice to raise sea levels many meters if it were to melt.

While melting sea ice doesn’t directly raise sea levels because it’s already floating on the water, several scientists told The Guardian about the side effects it could.

Sea ice helps mitigate the impact of storms on the ice attached to the coast. If it starts to disappear for longer, increased wave action could weaken those floating ice shelves that themselves stabilize the massive ice sheets and glaciers behind them on land.

One of the main areas of concern is the marked loss of ice in the Amundsen and Bellingshausen Seas in the west of the continent. Although the average amount of sea ice around the continent had increased by 2014, there were losses in these two adjacent seas. This is important because the region is home to the vulnerable Thwaites Glacier, known as the “Doomsday Glacier” because it contains enough water to raise sea levels by half a meter.

“We don’t want to lose sea ice where there are these vulnerable ice shelves and behind them ice sheets,” says Prof Matt England, an oceanographer and climatologist at the University of New South Wales. – We are likely starting to see signs of significant warming and sea ice retreat [в Антарктиде]. Seeing it reach those levels is definitely worrisome because we have these potentially reinforcing feedbacks.”

Data provided by scientists Dr. Rob Massom of the Australian Antarctic Division and Dr. Phil Reed of the Bureau of Meteorology shows that two-thirds of the continent’s coastline was open to water last month – well above the long-term average of about 50%.

“It’s not just about the area of ​​ice, it’s also about the duration of coverage,” says Dr. Massom. “If you remove the sea ice, you expose the floating edges of the ice to waves that can bend them and increase the chance that these ice shelves will break off. This then allows more ground ice to enter the ocean.”

Rob Massom and Phil Reed published a study last year in which they found that since 1979, the Amundsen Sea region has experienced longer ice-free periods and much of the coastline has been exposed to the open ocean.

Dr. Ted Scambos is a sea ice expert at the University of Colorado at Boulder who also works on Antarctic sea ice at the university’s National Snow and Ice Data Center, the world’s polar ice monitoring center. He said that the reduction in sea ice in Antarctica “makes the scientific community wonder if there is a process associated with global climate change.”

Antarctica is difficult to study, not only because of its remoteness, but also because of the problems of collecting data across the entire continent, subject to huge fluctuations in wind and storms from all directions.

Scambos noted: “Since 2016, there has been a fairly dramatic decline in sea ice, and especially with these record years in a row, as well as many months of near-record lows, this makes the scientific community wonder if there is a process associated with global change. climate.”

The expert stressed that while the most recent record may be partly due to the La Niña climate system, which tends to bring warmer winds to the continent’s peninsula, this does not explain losses elsewhere.

“We’re still trying to figure out what’s changed now,” he says. “But it is clear that shrinking sea ice will have an impact. This will have an impact on the continental ice because most of the coast will be exposed.”

For years, Antarctica seemed to baffle some climate models as sea ice – on average – increased slightly before the 2016 catastrophe.

Dr. Ariaan Puric, a climatologist at Monash University, is studying why the sea ice didn’t behave the way some expected. She said it was likely caused by changing winds and, counterintuitively, meltwater from land entering the ocean, making it easier for the ice to form.

One study found that ocean warming also contributed to the sudden drop in sea ice in 2016. “All models assume that as the climate warms, we expect Antarctic sea ice to shrink,” she says. There is a widespread consensus on this. So this low sea ice level is consistent with what climate models are showing.”

Antarctic scientists are now struggling to figure out what’s going on. Are melting sea ice and successive record lows just a natural phenomenon on a continent notoriously difficult to study? Or are these records just another clear sign that a climate crisis is hitting the frozen continent?

“Antarctica may seem remote, but changes around it could affect the global climate, and melting ice sheets are affecting coastal communities around the world,” says Dr. Puric. “Everyone should be concerned about what is happening in Antarctica.”