996. The Global Impact of Sea Ice Melting

Sea ice acts as a buffer between the ocean and the atmosphere. When sea ice forms, the water becomes fresher, displacing saltier, colder, and heavier seawater, which contributes to global ocean circulation and stabilizes the Earth's climate. Sea ice, with its bright surface, reflects sunlight and cools the Earth. However, once it melts, the dark surface of the water absorbs solar energy and warms the ocean and the atmosphere.

Antarctic ice grows and melts in annual cycles, reaching its minimum extent during the Southern Hemisphere summer. According to NASA, the annual minimum extent in 2024 was recorded on February 20, the second lowest on record in terms of satellite observations, reflecting a long-term trend of sea ice decline.

Historically, the amount of sea ice surrounding Antarctica has varied widely from year to year, while the long-term average over 10-year periods has remained relatively stable. In recent years, however, Antarctic sea ice has been melting rapidly, raising concerns among scientists that the long-term stable trend of climate change may be shifting. In the past seven years, the minimum sea ice record for Antarctica has been broken three times. The minimum extent recorded on February 20, 2024, is 30% lower than the 1981–2010 late-summer average, a difference equivalent to the area of the US state of Texas.

On the other side of the globe in the Arctic Ocean, the maximum winter sea ice extent is consistent with a 46-year downward trend, with the Arctic Ocean's maximum winter sea ice extent observed on March 14 this year, losing an area equivalent to that of Alaska since 1979.

Due to the ice-albedo feedback (link in Japanese), significant temperature changes above the global average have already been observed in the Arctic Ocean (link in Japanese). Under global warming, the summer sea ice extent in the Arctic Ocean has been reduced by half over the past 40 years, and the loss of sea ice is expected to continue at an accelerating rate, suggesting that a critical tipping point may be reached in the near future, at which point the change will become uncontrollable. It has been suggested that the increased atmospheric exchange between the Arctic and mid-latitude regions may lead to an increase in extreme weather events such as severe winters and heavy rainfall in the mid- to high-latitude regions. According to one study, Arctic warming and atmospheric variations are the mechanisms that lead to the "warm Arctic, cold East Asia" (WACE) teleconnection. 

In contrast to the Arctic, recent observations around Antarctica, which is isolated from other continents and reportedly less affected by climate change, suggests that an ice-albedo feedback is also imminent in the Southern Hemisphere. The area around Antarctica is said to be the most active sea-ice formation site and serves as the starting point for global ocean circulation. The signs of sea ice melting in Antarctica raise concerns that it could accelerate global climate change through its impact on ocean circulation.

Contributor: IIYAMA Miyuki (Information Program)