In 2023, Antarctic sea ice fell to historically low levels, prompting researchers to use CMIP6 climate models to assess the rarity of the event and its link to climate change. The study found that without climate change, such a drastic decrease would be extremely rare, but current climate conditions made it more likely. The research suggests that a steady decline in sea ice could have profound implications for weather patterns and marine ecosystems, making continued studies essential to understanding and predicting future changes.
Antarctic sea ice reached record lows in 2023, with studies showing climate change significantly increased the likelihood of this event. The potential long-term reduction in sea ice poses serious consequences for global weather and marine life.
In 2023, Antarctic sea ice shrank to historic lows, with winter ice cover falling more than 2 million square kilometers below normal – roughly equivalent to ten times the size of the United Kingdom. This sharp decline was particularly surprising given the continued increase in sea ice that had been observed through 2015, making the sudden decline all the more unexpected.
Using a large climate data set called CMIP6, BAS researchers investigated this unprecedented loss of sea ice. They analyzed data from 18 different climate models to understand the probability of such a significant reduction in sea ice and its relationship to climate change.
Lead author Rachel Diamond explained that while the 2023 extreme low sea ice had been made more likely by climate change, it was still considered very rare according to models.
She says: “This is the first time this large set of climate models has been used to find out how unlikely the 2023 low sea ice really was. We only have forty-five years of satellite measurements of sea ice. sea, which makes it extremely difficult to assess changes in sea ice extent. This is where climate models come into their own.
According to the models, the minimum extent of sea ice would be a one-in-2000-year event without climate change. This tells us that the event was very extreme – anything less than one in 100 is considered extremely unlikely.”
Caroline Holmes, a co-author of the study, said: “Strong climate change – ie. the temperature changes we’re already seeing—and those expected if emissions continue to rise rapidly—in models makes it four times more likely that we’ll see such a large decline in sea ice extent. This suggests that the extreme low of 2023 was made more likely by climate change.”
Long-term consequences and predictions for the future
The researchers also used the models to see how well sea ice is likely to recover. By looking at similar events in models, the authors found that after such extreme sea ice loss, not all of the sea ice around Antarctica returns—even after twenty years. This adds model evidence to existing observational evidence that low sea ice in recent years may signal a sustained regime change in the Southern Ocean.
Louise Sime, a co-author of the study, says: “The impacts of Antarctic sea ice remaining low for more than twenty years would be profound, including on local and global weather and on the unique ecosystems of the Southern Ocean – including whales and penguins”.
Satellite recordings of Antarctic sea ice began in late 1978, and from then until 2015, Antarctic sea ice extent increased slightly and steadily. In 2017, Antarctic sea ice reached a record low and has been followed by several years of relatively low sea ice extent.
There are many complex and interacting factors affecting Antarctic sea ice, making it difficult to clearly understand why 2023 was such a record year. Recent studies have highlighted 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 changes in north-south winds and storm systems also played a role.
Antarctic sea ice is a critical factor in our overall understanding of climate change. The formation of sea ice around the Antarctic acts as an engine for ocean currents and influences weather patterns. It also protects the exposed edges of the ice shelves from waves, curbing Antarctica’s contribution to sea level rise. Sea ice is also very important to marine life – scientists have observed catastrophic breeding failures of emperor penguin colonies due to low sea ice in recent years.
Therefore, studies like this are critical to finding out how likely rapid sea ice losses are and whether sea ice is likely to remain low over the coming decades.
Reference: “CMIP6 models rarely simulate Antarctic sea ice anomalies as large as observed in 2023” by Rachel Diamond, Louise C. Sime, Caroline R. Holmes and David Schroeder, 20 May 2024, Geophysical Research Letters.
DOI: 10.1029/2024GL109265
