The continent's fringing waters witness a massive shift each year, with sea ice peaking at about 18m sq km each September before dropping to just above 2m sq km by February. "We are seeing less ice everywhere. It's a circumpolar event."
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| Photograph: David Merrion |
In the southern hemisphere summer of 2022, the amount of sea ice dropped to 1.92m sq km on 25 February - an all-time low based on satellite observations that started in 1979. "Because sea ice is so reflective, it's hard to melt from sunlight. But if you get open water behind it, that can melt the ice from underneath," says Hobbs.
The fate of Antarctica - especially the ice on land - is important because the continent holds enough ice to raise sea levels by many metres if it was to melt.
While melting sea ice does not directly raise sea levels because it is already floating on water, several scientists told the Guardian of knock-on effects that can. Sea ice helps to buffer the effect of storms on ice attached to the coast. Antarctic sea ice hit a stunning record-low minimum at the end of February, dropping below 772,000 square miles for the first time since satellites began observing the southern continent more than 40 years ago.
A study published yesterday in the journal Advances in Atmospheric Sciences points to a perfect storm of factors that sent Antarctic sea ice spiraling downward in the past year.
Guardian
For 44 years, satellites have helped scientists track how much ice is floating on the ocean around Antarctica’s 18,000km coastline.
The continent’s fringing waters witness a massive shift each year, with sea ice peaking at about 18m sq km each September before dropping to just above 2m sq km by February. But across those four decades of satellite observations, there has never been less ice around the continent than there was last week.
“By the end of January we could tell it was only a matter of time. It wasn’t even a close run thing,” says Dr Will Hobbs, an Antarctic sea ice expert at the University of Tasmania with the Australian Antarctic Program Partnership.
“We are seeing less ice everywhere. It’s a circumpolar event.” In the southern hemisphere summer of 2022, the amount of sea ice dropped to 1.92m sq km on 25 February – an all-time low based on satellite observations that started in 1979. But by 12 February this year, the 2022 record had already been broken.
The ice kept melting, reaching a new record low of 1.79m sq km on 25 February and beating the previous record by 136,000 sq km – an area double the size of Tasmania. In the southern hemisphere’s spring, strong winds over western Antarctica buffeted the ice.
At the same time, Hobbs says large areas in the west of the continent had barely recovered from the previous year’s losses. “Because sea ice is so reflective, it’s hard to melt from sunlight. But if you get open water behind it, that can melt the ice from underneath,” says Hobbs.
Hobbs and other scientists said the new record – the third time it’s been broken in six years – has started a scramble for answers among polar scientists. The fate of Antarctica – especially the ice on land – is important because the continent holds enough ice to raise sea levels by many metres if it was to melt.
While melting sea ice does not directly raise sea levels because it is already floating on water, several scientists told the Guardian of knock-on effects that can. Sea ice helps to buffer the effect of storms on ice attached to the coast.
If it starts to disappear for longer, the increased wave action can weaken those floating ice shelves that themselves stabilize the massive ice sheets and glaciers behind them on the land.
Scientific American
Antarctic sea ice hit a stunning record-low minimum at the end of February, dropping below 772,000 square miles for the first time since satellites began observing the southern continent more than 40 years ago. Now scientists say they’ve untangled the reasons why.
A study published yesterday in the journal Advances in Atmospheric Sciences points to a perfect storm of factors that sent Antarctic sea ice spiraling downward in the past year. Some involve natural climate cycles—while others may be influenced by human-caused climate change.
A combination of La Niña conditions and other climate fluctuations in the Southern Hemisphere helped strengthen a natural weather pattern in the Southern Ocean known as the Amundsen Sea Low, or ASL.
The ASL is kind of like a permanent hurricane, swirling off the coast of West Antarctica. It’s always there, but it’s sometimes stronger and sometimes weaker depending on other climate conditions. When the ASL is stronger, it often has a destructive effect on Antarctic sea ice.
At the same time, oceans worldwide reached their hottest levels on record in 2021 (Climatewire, Jan. 12). And the Southern Ocean is exhibiting some of the highest levels of long-term warming. That’s an added threat to Antarctic sea ice, researchers have warned.
Warmer waters can thin the ice from the bottom up, which may make it break more easily under stress and melt faster during the summer months.
The combination of long-term ocean warming, plus the strong ASL and other natural climate patterns in the Southern Hemisphere during the past year, likely set up the right conditions for strong melting as the Antarctic summer approached.
Sea ice was thinner than normal to begin with in parts of the Southern Hemisphere in 2021. It also began melting earlier than usual at the start of the Antarctic spring in September. Thanks to the intense ASL and other stronger-than-usual wind patterns around Antarctica, sea ice in parts of the Southern Ocean drifted rapidly north into warmer waters, where it melted faster than usual.
As the ice disappeared, the ocean was able to absorb more sunlight and heat, further warming up the waters and accelerating the melting.