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Global sea ice cover dipped to a new record low last week.
Over the five-days leading up to February 13, the combined extent of Arctic and Antarctic sea ice dropped to 15.76 million sq km, down from the previous five-day record low of 15.93 million sq km in January-February 2023, according to BBC analysis of data from the US National Snow and Ice Data Center (NSIDC).
Sea ice refers to the free-floating ice in the polar regions. While it generally expands during the winter and melts in the summers, some sea ice remains year-round. Note that this is different from icebergs, glaciers, ice sheets, and ice shelves, which form on land.
Sea ice plays a crucial role in cooling the planet by trapping existing heat in the ocean, and thus precluding it from warming the air above. Therefore, a reduction in sea ice cover can have disastrous consequences for Earth.
Currently, Arctic sea ice is at its lowest recorded extent for the time of year. Meanwhile, Antarctic sea ice is close to a new low, based on satellite records going back to the late 1970s. But given historical trends, this is not all that surprising. Since the late 1970s, NSIDC has estimated that some 77,800 sq km of sea ice has been lost per year.
Between 1981 and 2010, Arctic sea ice extent in September — when it reaches its minimum extent — shrunk at a rate of 12.2% per decade, according to the National Aeronautics and Space Administration (NASA).
In the Antarctic, the situation is a bit different. Until 2015, the region actually witnessed a slight year-on-year increase in sea ice. Between late 2014 and 2017, however, the Antarctic lost two million square km of sea ice — an area equivalent to roughly four times the size of Spain, according to the Copernicus Marine Service. Sea ice levels again increased in 2018.
In 2023, maximum Antarctic sea ice reached historically low levels. Sea ice cover was more than two million sq km lower than usual — an area about 10 times the size of the UK.
Last year, the cover was higher than in 2023 but still 1.55 million sq km below the average maximum extent from 1981-2010.
Experts suggest that the 2025 low could be due to a combination of warm air, warm seas and winds breaking apart the ice, the BBC reported.
Antarctic sea ice is particularly vulnerable to ice-breaking winds. Unlike Arctic ice, it is surrounded by the ocean instead of continents and is thus more mobile, and also comparatively thinner. The situation has been made worse this year due to warmer air and warmer waters towards the end of the southern hemisphere summer (December to February).
Higher air temperatures led to the melting of the edges of the Antarctic ice sheet — also known as ice shelves — which extend over the ocean. “[The] ongoing ocean warming is setting the backdrop to all of this,” Tom Bracegirdle, research scientist at the British Antarctic Survey, told the BBC.
In the Arctic, where winter lasts from November to February, sea ice remained low because of a delayed freezing around the Hudson Bay, a large saltwater body in northeastern Canada. The delay occurred as unusually warm oceans took a longer time to cool down.
The region also witnessed some storms which broke apart ice around the Barents Sea, located off the northern coasts of Norway and Russia, and the Bering Sea, the stretch between Alaska and Russia. Experts say that Arctic ice has become thinner and more fragile over the years, and hence more susceptible to breaking by storms.
Higher than usual air temperatures in areas such as Svalbard, Norway, resulted in further loss of sea ice.
Less sea ice cover means that more water is getting exposed to the Sun and more heat (solar radiation) is getting absorbed, leading to a further rise in temperatures. Notably, sea ice keeps temperatures down in the polar regions, as its bright, white surface reflects more sunlight back to space than liquid water. The loss of sea ice cover could be one of the reasons why the polar regions are getting warmer at a faster rate than the rest of the world.
Studies have found that melting sea ice is also slowing down the flow of water through the world’s oceans. This is happening because freshwater from melting ice enters the ocean, and reduces the salinity and density of the surface water, thereby diminishing that downward flow to the sea’s bottom. A slowdown of ocean overturning can severely impact the global climate, the marine food chain, and the stability of ice shelves.
