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 reduction would be extremely rare, but current climate conditions made it more likely. The research suggests that lasting sea ice decline could have profound effects on weather patterns and marine ecosystems, making ongoing studies essential for understanding and predicting future changes.
Antarctic sea ice will reach a record low in 2023, with research showing that climate change will significantly increase the likelihood of this event. The potential long-term reduction in sea ice has serious consequences for global weather and marine life.
In 2023, Antarctic sea ice shrank to record low levels, with winter ice cover falling more than 2 million square kilometers below normal – roughly equivalent to ten times the area of Britain. This significant decline was particularly striking given the steady increase in sea ice observed through 2015, making the abrupt decline even more unexpected.
Using a large climate dataset called CMIP6, BAS researchers investigated this unprecedented sea ice loss. They analyzed data from 18 different climate models to understand the likelihood of such a significant reduction in sea ice and its link to climate change.
Lead author Rachel Diamond explained that while the extremely low sea ice of 2023 was made more likely by climate change, it was still considered very rare according to the models.
She says: “This is the first time this large suite of climate models has been used to find out how unlikely the 2023 low sea ice actually was. We have only forty-five 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.
According to the models, the record-breaking minimum sea ice extent would be a one-in-2,000-year event without climate change. This tells us that the event was very extreme; anything less than one in a hundred is considered exceptionally unlikely.”
Caroline Holmes, co-author of the study, said: “Strong climate change – meaning the temperature changes we are already seeing, and the changes we expect if emissions continue to rise rapidly – makes it four times more likely in the models that we have such a large decrease in the extent of the sea ice. This suggests that the extreme low of 2023 has become more likely due to climate change.”
Long-term consequences and future projections
The researchers also used the models to see how well the sea ice is likely to recover. By looking at similar events in the models, the authors found that after such an extreme sea ice loss, not all the sea ice around Antarctica returns – even after 20 years. This adds modeling evidence to existing observational evidence that low sea ice in recent years could signal lasting regime change in the Southern Ocean.
Louise Sime, co-author of the study, said: “The impact of Antarctic sea ice remaining low for more than two decades would be significant, including on local and global weather and 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 the extent of Antarctic sea ice increased slightly and steadily. In 2017, Antarctic sea ice reached a record low, 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 get a clear understanding of why 2023 was such a record year. Recent studies have highlighted the important role of ocean processes and heat stored beneath 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 crucial factor in our overall understanding of climate change. Sea ice formation 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 crucial for marine life. Scientists have observed catastrophic breeding failures of emperor penguin colonies in recent years due to low sea ice.
Studies like these are therefore crucial to find out 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 C. Sime, Caroline R. Holmes and David Schroeder, May 20, 2024, Geophysical research letters.
DOI: 10.1029/2024GL109265