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Things are not looking good for global sea ice.
In February 2025, Antarctic and Arctic sea ice combined hit a new low scientists reported.
Arctic sea ice, in its winter phase, has just hit its maximum extent. It is the lowest in the 47-year satellite record.
Antarctic sea ice, in its summer phase, reached a near-record low minimum extent in early March.
The ice edge cracking up. Photo: Anthony Powell
A regime shift for Antarctic sea ice?
Arctic sea ice has long been in decline. Both the area of ice coverage and its thickness have been shrinking. Recent modelling suggests that the first single ice-free summer day in the Arctic could occur before 2030.
However, while Arctic sea ice has been declining, Antarctic sea ice had been holding steady, in defiance of what climate models predicted - until recently.
The US National Snow and Ice Data Center has been monitoring sea ice extent using satellites since 1979.
Antarctic sea ice extent with the last four years highlighted. Photo: National Snow and Ice Data Centre
From 1979 to 2014, total Antarctic sea ice increased by about 1 percent per decade. In fact, there were three consecutive record highs for winter sea ice extent in 2012, 2013 and 2014.
But from 2016 onwards the ice began to decrease, and in 2023 a new record low winter maximum extent was reached, alarming scientists.
This has been followed up with another near-record low in 2024.
A snow petrel flies above an iceberg. Photo: Anthony Powell
When you consider that six-million-year-old ice sheet cores have been recovered from Antarctica, 47 years of satellite record doesn't sound all that long. It is possible that the recent seasons of low sea ice are just a feature of Antarctica's natural variability.
But that's not what researchers in the field think.
When they run the numbers, it looks to scientists like there's a major regime change in Antarctic sea ice, mostly likely in response to ocean warming.
An ice floe with an airfield flag still on it floats past Scott Base. Photo: James Brundell
What happens when there is less Antarctic sea ice?
Sea ice has four important characteristics. It is white and can reflect sunlight back into space during the Antarctic summer, therefore preventing further ocean warming. Reduced sea ice means the beginning of an unfortunate feedback loop of warming.
It also forms an insulating blanket, preventing heat energy from moving from the ocean into the atmosphere during the cold, dark Antarctic winter. Without the blanket, more heat movement would increase storminess.
The formation of sea ice also makes the surrounding water saltier, as salt is pushed out when water freezes. If less sea ice forms, there is less of this cold, dense, briny water, called 'Antarctic Bottom Water', that powers global deep ocean currents.
Sea ice meets the Erebus ice tongue glacier. Photo: Claire Concannon / RNZ
Finally, there's the shielding effect of land-fast sea ice. This ice is attached to either the land, or the front of glaciers or floating ice shelves. It forms a barrier, protecting these huge slabs of ice from wave action. In a future with less of this shielding ice, it is likely that there will be more icebergs calving from the edges of ice shelves, speeding up ice sheet flow and melt, and contributing to sea level rise.
What about the penguins?
Less Antarctic sea ice will also impact those critters who need it as part of their life cycle. This includes ice-associated microalgae, some species of ice fish, Weddell seals, and emperor penguins.
In 2022, the fate of emperor penguins in a world with less sea ice hit the headlines. A satellite image study revealed that four penguin colonies in the Bellingshausen Sea, west of the Antarctic Peninsula, probably suffered total breeding failure.
Photo: Vladimi Seliverstov
The land-fast sea ice broke up before the penguin chicks were likely to have fledged. While it was unusual for there to be such loss of sea ice in this region, sometimes penguin colonies do suffer these breeding failures - scientists term it 'blinking'.
Looking at where these penguins breed around the whole of Antarctica, it is likely that in the short term they will be able to adapt and use land-fast sea ice that sticks around.
The long-term future is not so hopeful, with modelling suggesting that if we continue on a high greenhouse gas emission trajectory, more than 90 percent of emperor penguin colonies will be all but extinct by the end of the century.
This series was made with travel support from the Antarctica New Zealand Community Engagement Programme.
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