Changing times in Antarctica
In February 2025, the world hit a new low for global sea ice extent. Arctic sea ice has been declining for several decades now, but Antarctic sea ice had been holding steady until recently.
With low summer sea ice extents for 4 years in a row, it appears that Earth’s warming has kicked Antarctic sea ice into a new regime. This will have impacts at a local ecosystem level through to impacts on the global climate.
Introducing Changing times in Antarctica
In this short video, RNZ science communicator Dr Claire Concannon summarises, Changing times, an episode in her Voice of the Sea Ice podcast series. Claire asks Antarctic researchers how they feel about the implications of their work.
Select here to view the video transcript and copyright information.
Global sea ice decline
In February 2025, scientists reported that Antarctic and Arctic sea ice both hit a new low. Arctic sea ice extent is at its lowest in the 47-year satellite record. Antarctic sea ice hit an all-time low in 2023 and continues to show a decline when looking at records over the last four decades.
Changing times in Antarctica – podcast
RNZ science communicator Dr Claire Concannon presents her fifth episode of six in the Voice of the Sea Ice podcast series. Claire discusses the implications of sea ice decline in Antarctica and global warming and what it’s like to work on climate change science with Antarctic researchers.
Select here to view the video transcript, questions for discussion and copyright information.
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 has 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.
From 1979 to 2014, total Antarctic sea ice increased by about 1% per decade. 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.
Sea ice extent
This graph shows sea ice extent data (area of ocean with at least 15% sea ice concentration) for 2021–2025 and an average for 1981–2010 in grey.
This graph is from the interactive graph, courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder. The graph has multiple parameters that users can select or deselect to drill down into the data.
Scientists in the field considered that recent seasons of low sea ice may have been a feature of Antarctica’s natural variability. However, when looking at 6 million-year-old ice sheet cores and 47 years of satellite records and running the numbers, they think this is likely the start of a major regime shift, probably in response to ocean warming.
Researchers had anticipated through modelling that sea ice decline would already be well established before 2023. One theory is that, in a warming world, warmer water underneath the ice shelves, which are the floating extensions of the Antarctic ice sheet, increases the rate at which those ice shelves are melting. That adds extra fresh water to the top of the ocean – and the fresher the water, the easier it will form sea ice.
What happens when there is less Antarctic sea ice?
Antarctic bottom water and global ocean circulation
Major deep ocean currents circulate cold Antarctic bottom water (the blue line) out to the rest of the world. This is part of the ocean conveyor belt, moving warm tropical waters (in red) downwards and forcing cold, nutrient-rich waters upwards (in blue) and circulating water around the globe. Temperature and salinity drive these deep currents.
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 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 increases storminess.
The formation of sea ice also makes the surrounding water brinier, as salt is pushed out when water freezes. This powers the global deep ocean currents. If less sea ice forms, there is less of this cold, dense, briny water, called Antarctic bottom water, and that impacts the global deep ocean currents.
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, there will likely be more iceberg calving from the edges of ice shelves, speeding up ice sheet flow and melt and contributing to sea-level rise.
When I first came down here, people were starting to appreciate the role that Antarctica plays in our climate, but we hadn’t really got to the point of feeling alarmed. But over my time here and working within this community, really, the time for being enchanted by the science is kind of gone for me. It’s much more about the obligation to understand what on Earth is going on, how fast it’s happening, what the implications are for society as a whole, and making sure that I’m doing everything I can to help get that message out and make sure that people understand what our future is really turning into.
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.
Emperor penguin colony
An emperor penguin colony on Snow Hill Island, the east coast of the Antarctic Peninsula.
Emperor penguins need sea ice to breed. In 2023, it was reported that in four out of five breeding sites in one region of sea ice loss, no chicks survived.
In 2023, 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. Emperor penguins breed on land-fast sea ice. 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 a 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 in the short term they’ll be able to adapt and use land-fast sea ice that sticks around.
It’s really sad that we have done that and that we have known that we were doing that. We could have done something a long time ago, and we decided not to. And so that makes me really sad, but I choose to have hope and I choose to have optimism.
The long-term future is not so hopeful, with modelling suggesting that, if we continue on a high greenhouse gas emissions trajectory, more than 90% of emperor penguin colonies will be all but extinct by the end of the century.
Impacts on platelet ice
Platelet ice is a microalgae (phytoplankton) habitat, and these microscopic algae support the base of the marine food web in Antarctica.
Below the sea ice
View from under the sea ice in McMurdo Sound, with the sub-ice platelet layer extending down into the water. The green-yellow tinge shows thriving microalgae living within the reef-like structure.
Text by Jacqui Stuart and Natalie Robinson, from their article in The Conversation.
In the short to intermediate term, scientists anticipate there will be more platelet ice because the melting of the Ross Ice Shelf will result in more really cold water that is needed to form platelet ice. But in the long-term future, if more warm water gets in under the Ross Ice Shelf, the platelet ice volume will start declining. Both of those scenarios have implications for Antarctic ecosystems.
Student activities
These activities visually demonstrate the implications of melting:
Related content
For many people, climate change is a difficult subject that can cause anxiety or sadness. For a selection of resources to ensure educator and student wellbeing, take a look at our Hauora board on Pinterest.
In our video Don’t give up hope, educators and scientists speak about taking action in the local environment to make a difference, build connections and gain hope for the future.
Voice of the Sea Ice is a six-part RNZ podcast series that delves into science research and adventure in Antarctica. Explore the other episodes:
A land of ice and ambition: Learn about different types of ice, crevasses and the work to map safe routes across Antarctica for scientists and their equipment.
The heartbeat of Antarctica: Meet and learn from some of the researchers studying the physics of the Antarctic annual sea ice cycle.
Antarctic life – microalgae: Introduces microalgae (zooplankton) that live on the bottom of the ice and among the platelet ice layer just below it.
Antarctic life – penguins, seals and fish: Scientists are investigating the Antarctic food web to better understand the interconnections.
Climate change – where to? Human-induced climate change is impacting Earth’s global systems, including ice melt in Antarctica. What is the world doing to combat it? Where does New Zealand fit in, and are we doing our bit as a nation?
For resources that provide a deeper exploration of other ice forms in Antarctica, go to Icebergs and Glaciers. Antarctic sea ice decline and modelling looks at sea ice around Antarctica, and Climate change, melting ice and sea level rise explores ice sheets and ice shelves.
Satellites are an important tool in many different types of research. Take a closer look at some research in Antarctica that has used satellites:
Use these articles below to explore how rising global temperature is causing both land ice and sea ice to melt:
Rising seas – a Connected article
Antarctica tipping points looks at the irreversible changes we could be facing if we fail to keep global warming below 2°C.
Useful links
Read Sea ice loss linked to salty Southern Ocean surface – Expert reaction from the Science Media Centre to hear more from Dr Inga Smith, Professor Wolfgang Rack and Dr Natalie Robinson among others.
The world’s biggest iceberg ran aground in March 2025. Get up close and personal and listen to the Voice of the Iceberg miniseries.
Read about the World Meteorological Organisation’s State of the Global Climate Report in this RNZ article.
The world is experiencing ice loss from its glaciers. New Zealand’s glaciers have shrunk by 29% since 2000. Listen to The annual snowline survey to learn how our glaciers are monitored.
In September 2023, scientists registered their alarm at evidence of declining ice in Antarctica, and in 2024, Antarctic sea ice maximum extent finished at second lowest. In 2025, the declines in both Antarctica and the Arctic hit a new low. Learn more in the articles Antarctic sea ice minimum hits a near-record low, again and Global sea ice hit all time minimum in February, scientists say.
The US National Snow and Ice Data Center has been monitoring sea ice extent using satellites since 1979 and has regularly updated visualisations and data on Antarctica and the Arctic here. These interactive graphs allow the user to select years of interest – make sure to select the right tab for each pole.
Emperor penguins face a bleak future – but some colonies will do better than others is an article by Dr Sara Labrousse (French Polar Institute) and Associate Professor Michelle LaRue.
The following links are to academic papers that underpin some of the statements made in this resource. While they are at a tertiary level, these will be of interest to educators and senior students. We recommend reading the abstracts and conclusions for an overview and understanding of the research:
The first ice-free day on the Arctic Ocean could occur before 2030
A twenty-first century structural change in Antarctica’s sea ice system looks at the evidence of a regime change in Antarctic sea ice, and Record low Antarctic sea ice coverage indicates a new sea ice state collates evidence that shows it is likely a response to ocean warming
Record-low Antarctic sea ice in 2023 increased ocean heat loss and storms
Antarctic ice shelf disintegration triggered by sea ice loss and ocean swell
Unavoidable future increase in West Antarctic iceshelf melting over the twenty-first century
Record low 2022 Antarctic sea ice led to catastrophic breeding failure of emperor penguins
The call of the emperor penguin: Legal responses to species threatened by climate change
Acknowledgement
This resource is adapted from the work of Dr Claire Concannon for the RNZ podcast series Voice of the Sea Ice. The series was made with travel support from the Antarctica New Zealand Community Engagement Programme.
