The sea ice was fundamental to ecosystems and may play a role in protecting the Antarctic ice sheet from the effects of ocean heat, he said. When the ice sheet melts it adds to global sea levels.
On Feb. 25, sea-ice extent — a measurement of the ocean’s sea ice — around Antarctica shrank to less than 772,000 square miles (2 million square kilometers) for the first time since scientists began recording it in 1979, the National Snow and Ice Data Center (NSIDC) announced March 8.
Antarctic sea ice is challenging to study because of the huge changes that occur. About 15m sq km of sea ice – an area double the size of Australia – grows and substantially melts each year. The ice can be influenced by the strength and direction of winds as well as heat in the atmosphere and ocean.
While warming global temperatures may be a factor, Antarctic sea ice is highly variable. The shrinking is likely natural, and partly due to strong winds pushing some sea ice farther north into warmer waters, Nature reported. “I think much, if not all, of the event can be ascribed to natural variability,” Walt Meier, a senior research scientist at the NSIDC, told Nature.
Data from the US National Snow and Ice Data Center showed the Southern Ocean sea ice coverage had fallen below 2m sq km for the first time since satellite measurement began more than 40 years ago.
Sea ice is frozen seawater that floats on the surface of the ocean. Unlike icebergs and other ice formations that break away from land, sea ice forms on the ocean and is usually covered in snow, according to the NSIDC. The new data captured the annual late-summer minimum sea-ice extent, which gives a measurement of the area of ocean that has sea ice when coverage is at its lowest for the year after the ice melts in the Southern Hemisphere summer.
Dr Walt Meier, a senior research scientist with the NSIDC, said it coincided with strong winds over part of the Ross Sea that had pulled ice to the north, where it melted in warmer waters or was broken up by waves.
Antarctic sea ice varies considerably from year to year, and the NSIDC has not found a statistically significant trend in one direction or another using satellite data. This year was the lowest minimum sea-ice extent on record, but the highest minimum sea-ice extent was recorded in 2015.
Meier said the changes in Antarctic sea ice were “still really a muddled signal at this stage”. “Whether this is the start of [a decline] it’s still too early to say, but it’s definitely worth watching”, Meier said.
Antarctica is surrounded by water, and wind and ocean currents isolate the continent from weather patterns elsewhere on Earth, according to the NSIDC. The Arctic, in contrast, is surrounded by land and is better connected to other climate systems. Arctic sea-ice extent is, therefore, more important for deciphering global climate trends and highlighting the warming impact of climate change.
This pushed the sea ice extent – the area of the ocean covered by at least 15% floating ice – to below the previous record low set in 2017. But scientists expressed caution about attributing the retreat to the increase in global temperatures linked to greenhouse gas emissions.
Satellite images of the Arctic show a clear, linear sea-ice decline over the past 44 years. A comparison of satellite records from February 1979 and February 2022 showed that Arctic sea-ice extent has declined by 703,000 square miles (1.82 million square km), according to the latest NSIDC data. That’s more ice than there is land in Alaska, which has 586,000 square miles (1.5 million square km) of land, according to Alaska’s official state website.