The sea ice surrounding Antarctica has predictably recorded this year the smallest frozen surface area recorded so far for these dates (when it reaches its highest level in the southern winter). This is what this year's results show. Scientists fear that global warming could lead this region to enter a new phase marked by the disappearance of ice with far-reaching consequences.
On September 10, Antarctic sea ice reached its maximum annual extent, at 16.96 million square kilometers, but it turned out to be the smallest extent since records began in 1979.
This is a preliminary announcement, according to the United States National Snow and Ice Data Center (NSIDC). It is not ruled out that changing winds or late ice growth could still increase the extent of the frozen sea.
This year's peak Antarctic sea ice is 1.03 million square kilometers below the previous record low, set in 1986. It is also 1.75 million square kilometers below Antarctica's average maximum extent. between 1981 and 2010.
It is the first time that the extent of sea ice has not exceeded 17 million square kilometers.
Every September, Antarctic sea ice reaches its maximum extent. The average between 1981 and 2010 was 18.71 million square kilometers
The maximum ice extent in Antarctica is one of the earliest, as it was reached 13 days before the average date it usually occurs (which is usually between September 18 and 30).
What has been the evolution this year?
From the beginning of April 2023, sea ice expansion was very slow and from early to mid-August growth slowed even further, ranking as the second lowest year according to satellite records, with a difference of almost 1.5 million square kilometers between 2023 and 1986. After that period, ice growth accelerated and narrowed the gap to about 1 million square kilometers.
While climatic conditions such as winds and temperature control much of the daily variation in ice extent, the long-term downward trend is a matter of much debate.
Since August 2016, the trend indicates a sharp drop in almost every month.
There is some concern that this could be the start of a long-term trend of declining Antarctic sea ice, as oceans are warming globally and mixing of warm water in the Southern Ocean polar cap could continue. The Southern Ocean and its sea ice are an important component of the Earth's energy balance, reflecting sunlight back into space and supporting a rich ice-edge ecosystem.
Furthermore, if the drastic decline in sea ice continues to the summer minimum of 2024 and beyond, a large part of the Antarctic coast will be exposed to the waves and storms typical of the marine climate. This can cause two opposite impacts: on the one hand, causing the erosion of the more “perpetual” coastal ice and ice shelves, which destabilizes the ice sheet; and, on the other hand, greater accumulation near the coast, which would partially offset the threat of sea level rise.
Will Hobbs, a sea ice scientist at the University of Tasmania, said that since April the rate of growth of Antarctic sea ice had been “very, very slow”. "In May it was pretty obvious we were in for something spectacular," he added.
This expert points out – in statements to The Guardian – that the losses of sea ice in the Ross Sea region were probably due to the fact that the winds had pushed the ice against the continent and brought warm air. But climate couldn't explain why ice was lost on the rest of the continent.
Antarctic sea ice goes through an annual cycle that reaches its lowest extent each February and its highest levels in September.
Scientists are still trying to unravel the reasons for this dramatic series of records, where natural variability and global warming are likely to combine.
Hobbs said that in his opinion it cannot yet be established with complete certainty that all this is a consequence of global warming, although he said the loss of sea ice was consistent with climate change projections.
The US National Snow and Ice Data Center said sea ice losses since 2016 are likely related to warming of the upper ocean.
There is some concern that this could be the start of a long-term trend of declining Antarctic sea ice, as oceans are warming globally and mixing of warm water in the Southern Ocean polar cap could continue.
Thousands of emperor penguin chicks likely died last year after the breakup of generally stable sea ice in four of their colonies.
Ariaan Purich, a climate scientist specializing in Antarctica and the Southern Ocean at Monash University, said the upper 300 meters of the Southern Ocean around the continent had been noticeably warmer since 2016.
"But why sea ice has been lower than it has ever been on record, we still don't fully understand," he added.
The loss of sea ice can have far-reaching consequences for the planet.
Sea ice reflects the sun's energy into space. With less sea ice, more of the ocean is exposed to the sun's energy, causing further warming of the Southern Ocean and greater ice loss.