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Record low levels of Antarctic sea ice in 2023 were extremely unlikely without climate change, says BAS





The record low levels of sea ice around Antarctica in 2023 were extremely unlikely to have happened without the influence of climate change, scientists at the British Antarctic Survey (BAS) have found.

It would be a one-in-a-2,000-year event without climate change - and four times more likely with its effects, they reported in the journal Geophysical Research Letters on Monday (20 May).

Sea ice in Marguerite Bay. Picture: BAS
Sea ice in Marguerite Bay. Picture: BAS

There was more than two million square kilometres less ice than usual in winter - 10 times the size of the UK - following decades of steady growth in sea ice up to 2015, which made the sudden decline more surprising.

Analysing 18 climate models to understand the probability, they concluded it was still a very rare event, even though it was made more likely by climate change.

Lead author Rachel Diamond said: “This is the first time this large set of climate models has been used to find out how unlikely 2023’s low sea ice actually was. We only have 45 years of satellite measurements of sea ice, which makes it extremely difficult to evaluate changes in sea ice extent. This is where climate models come into their own.”

Caroline Holmes, a co-author on the study, said: “Strong climate change – ie the temperature changes we’re already seeing, and those expected if emissions continue to rise rapidly - in the models makes it four times more likely that we see such a big decline in sea ice extent. This suggests that 2023’s extreme low was made more likely by climate change.”

Sea ice reflections around Rothera Point. Steve Gibbs
Sea ice reflections around Rothera Point. Steve Gibbs

Examining similar events in the models, the authors found that after such extreme sea ice loss, not all of the sea ice around Antarctica returns, even after 20 years.

This follows existing observational evidence that the last few years’ low sea ice could signal a lasting regime shift in the Southern Ocean.

Co-author Louise Sime said: “The impacts of Antarctic sea ice staying low for over 20 years would be profound, including on local and global weather and on unique Southern Ocean ecosystems - including whales and penguins.”

Scientists have observed catastrophic breeding failures of emperor penguin colonies in recent years due to low sea ice.

Satellite records of Antarctic sea ice began in late 1978. Between then and 2015, it increased slightly and steadily but in 2017 it reached a record low - and that has been followed by several years of relatively low sea ice extent.

Aerial view of the edge of the Brunt Ice Shelf. A colony of emperor penguins are on the remains of sea ice. Picture: Constantino Listowski, BAS
Aerial view of the edge of the Brunt Ice Shelf. A colony of emperor penguins are on the remains of sea ice. Picture: Constantino Listowski, BAS

There are complex, interacting factors influencing Antarctic sea ice.

Recent studies have shown the important role of ocean processes and heat stored below the surface, and warm sea surface temperatures during the first half of 2023 may also have contributed. Strong variations in north-to-south winds and storm systems also played a role.

We do know that Antarctic sea ice is a key factor in understanding climate change.

Aerial view of sea ice. Picture: David Vaughan, BAS
Aerial view of sea ice. Picture: David Vaughan, BAS

Sea ice formation around the Antarctic is an engine for ocean currents and influences weather patterns. It also protects the exposed edges of ice shelves from waves, curbing Antarctica’s contribution to sea level rise.



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