Arctic sea ice has retreated to near-historic lows this summer, with researchers from NASA and the National Snow and Ice Data Center (NSIDC) reporting that the minimum extent for 2024 was reached on September 11. This decline continues a decades-long trend of shrinking and thinning ice cover in the Arctic Ocean.
This year, Arctic sea ice shrank to a minimal extent of 1.65 million square miles (4.28 million square kilometres), which is approximately 750,000 square miles (1.94 million square kilometres) below the average end-of-summer extent of 2.4 million square miles (6.22 million square kilometres) recorded between 1981 and 2010. Notably, the area difference exceeds the size of Alaska.
Sea ice extent is defined as the total area of the ocean that has at least 15% ice concentration.
A HISTORIC PERSPECTIVE
While this year’s minimum remained above the all-time low of 1.31 million square miles (3.39 million square kilometres) set in September 2012, it still marks the seventh-lowest extent in the satellite record. Since the late 1970s, when satellite observations began, Arctic sea ice has been declining at a rate of approximately 30,000 square miles (77,800 square kilometres) per year, according to the NSIDC.
COMPOSITION OF ARCTIC ICE
Scientists measure sea ice extent using data from passive microwave sensors aboard satellites in the Defense Meteorological Satellite Program, supplemented by historical data from the Nimbus-7 satellite.
According to Nathan Kurtz, Chief of NASA’s Cryospheric Sciences Laboratory, “Today, the overwhelming majority of ice in the Arctic Ocean is thinner, first-year ice, which is less able to survive the warmer months.” He emphasized that there is significantly less ice that is three years or older, indicating a worrying trend in the ice’s longevity and stability.
DECLINING THICKNESS
Recent measurements collected with spaceborne altimeters, including NASA’s ICESat and ICESat-2 satellites, reveal that much of the oldest and thickest ice has already vanished. New research from NASA’s Jet Propulsion Laboratory indicates that fall sea ice in the central Arctic now averages about 4.2 feet (1.3 meters) thick, down from a peak of 8.8 feet (2.7 meters) in 1980.
ANTARCTIC SEA ICE ALSO UNDER PRESSURE
In addition to the alarming conditions in the Arctic, sea ice in Antarctica is also tracking near-record lows for 2024. Despite being in a season where sea ice typically expands, the Antarctic region is projected to reach just over 6.6 million square miles (16.96 million square kilometres) of sea ice. This figure is significantly below the average maximum extent of 7.22 million square miles (18.71 million square kilometres) recorded between 1981 and 2010.
A Shift in Antarctic Trends
The minimal growth observed in 2024 continues a recent downward trend in Antarctic sea ice. Prior to 2014, there was a slight increase of about 1% per decade. However, after a spike in 2014, the growth has drastically declined, prompting scientists to investigate the causes behind this reversal. The ongoing loss of sea ice suggests a long-term shift in conditions in the Southern Ocean, likely attributed to global climate change.
Walt Meier, a sea ice scientist at the NSIDC, noted, “While changes in sea ice have been dramatic in the Arctic over several decades, Antarctic sea ice was relatively stable. But that has changed.” He added that it appears global warming has finally impacted the Southern Ocean.
FEEDBACK LOOP OF ICE LOSS
In both the Arctic and Antarctic, the loss of sea ice creates a feedback loop that exacerbates the situation. Sea ice reflects most of the sun’s energy back into space, while open ocean water absorbs about 90% of it. This exposure to sunlight increases water temperatures, further delaying the growth of sea ice. This phenomenon is known as ice-albedo feedback.
WARMING ARCTIC
The overall loss of sea ice contributes to increased heat in the Arctic, where temperatures have risen approximately four times the global average. As Nathan Kurtz emphasizes, the implications of these changes extend beyond mere statistics; they pose significant threats to ecosystems, wildlife, and human communities.
