In 2023, Antarctic sea ice declined to historic lows, prompting researchers to use CMIP6 climate models to assess the rarity of the event and its relationship to climate change. The study found that without climate change such a drastic reduction would be extremely rare, but current climate conditions make it more likely. The research suggests that permanent declines in sea ice could have profound implications for weather patterns and marine ecosystems, making ongoing research essential to understanding and predicting future changes.
Antarctic sea ice hit record lows in 2023, with studies showing climate change greatly increases the likelihood of that event. The potential long-term decline in sea ice has serious implications 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 significant decrease was particularly impressive given the steady increase in sea ice observed through 2015, making the sharp decline even 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 likelihood of such a significant reduction in sea ice and its relationship to climate change.
Lead author Rachel Diamond explained that while extreme low ice in 2023 has been made more likely by climate change, it is still thought to be very rare according to models.
She says: “This is the first time this large set of climate models has been used to understand how unlikely the 2023 sea ice low actually is. We only have forty-five years of satellite measurements of sea ice, making it extremely difficult to estimate changes in sea ice extent. This is where climate models come into play.
According to the models, the record-breaking minimum sea ice extent 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, 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 — make it four times more likely in the models to see such a big drop in sea ice volume. This suggests that the extremely low level of 2023 is made more likely by climate change.
Long-term consequences and future projections
The researchers also used the models to see how well the sea ice was likely to recover. Looking at 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 twenty years. This adds model evidence to existing observational evidence that the low sea ice of the past few years may signal a permanent regime change in the Southern Ocean.
Louise Syme, co-author of the study, said: “The impact 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 records of Antarctic sea ice began in late 1978, and between then and 2015, Antarctic sea ice extent increased slightly and steadily. In 2017, Antarctic sea ice reached a record low and was 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 oceanic processes and heat stored below the surface and warm sea surface temperatures in the first half of 2023 may also have contributed. Strong variations 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 Antarctica acts as a driver for ocean currents and influences weather patterns. It also protects the exposed edges of the ice shelves from waves, limiting Antarctica’s contribution to sea-level rise. Sea ice is also vital to marine life – scientists have seen catastrophic failures in the reproduction of emperor penguin colonies due to low sea ice levels in recent years.
Therefore, studies like this are critical to understanding how likely rapid sea ice losses are and whether sea ice is likely to remain low in the coming decades.
Reference: “CMIP6 models rarely simulate Antarctic winter sea ice anomalies as large as observed in 2023” by Rachel Diamond, Louise S. Syme, Caroline R. Holmes, and David Schroeder, 20 May 2024. Geophysical Research Letters.
DOI: 10.1029/2024GL109265
