Thursday, June 20, 2024

Antarctica’s record-low sea ice levels of 2023

New research has found that record-low levels of sea ice around Antarctica in 2023 were made at least four times more likely by climate change.

In July 2023, the extent of Antarctic sea ice during winter dropped to its lowest level since satellite records began in late 1978, with approximately 2.5 million square kilometers less than usual.

Researchers, led by the British Antarctic Survey (BAS), investigated the likelihood of such a significant reduction in sea ice and the role of climate change in making this event more probable.

Using climate datasets and models, the team found that Antarctic sea ice reaching historic lows would occur only once in over 2,000 years, or was “extremely unlikely” without climate change, which made the event more than four times likelier. For their analysis, they used global climate model data from the Coupled Model Intercomparison Project Phase 6 (CMIP6).

“This is the first time this large set of climate models has been used to determine 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,” said Rachel Diamond, lead author of the study published in the journal Geophysical Research Letters.

“According to the models, the record-breaking minimum sea ice extent would be a one-in-a-2000-year event without climate change. This tells us that the event was very extreme—anything less than one-in-100 is considered exceptionally unlikely,” Diamond said.

This drastic reduction followed decades of steady growth in sea ice up to 2015, making the sudden decline even more surprising, the researchers noted.

They explained that satellite records of Antarctic sea ice began in late 1978, and between then and 2015, Antarctic sea ice extent increased slightly and steadily. However, in 2017, Antarctic sea ice reached a record low, followed by several years of relatively low sea ice extent.

The researchers also examined how well sea ice is likely to recover after plunging to record-low levels.

The authors discovered that after such extreme sea ice loss, not all of the sea ice around Antarctica returns, even after 20 years. This provides model evidence to support existing observational evidence suggesting that the recent low sea ice levels in the last few years could indicate a lasting regime shift in the Southern Ocean and its ecosystems, they explained.

“The impacts of Antarctic sea ice remaining low for over 20 years would be significant, affecting local and global weather patterns, as well as unique Southern Ocean ecosystems, including whales and penguins,” said study co-author Louise Sime from the British Antarctic Survey.

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