'Unprecedented,' 'Gobsmacked', 'Unbelievable': Changes in Antarctica's sea ice could have dramatic impacts, says climate scientist Edward Doddridge

On Aug. 16, 1897, the  Research Vessel Belgica set sail from Antwerp, Belgium. The ship's destination — via Rio de Janeiro, Montevideo and then Punta Arenas, Chile — was Antarctica, a continent that until that time remained completely unexplored by westerners.

The new land was not kind to its visitors. Shortly after its arrival, the Belgica became stuck in the thick halo of pack ice that surrounded the continent. As the Antarctic's dayless winter set in, the ship's 18 man crew were pushed to their mental and physical limits, consuming penguin and seal meat to survive.

"We are as hopelessly isolated as if we were on the surface of Mars," wrote Frederick Cook, the Belgica's American physician, in 1898. "And we are plunging still deeper and deeper into the white Antarctic silence."

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In the days of faint sunlight that came in the following spring, the ship's desperate, disease-ridden crew resorted to dropping sticks of dynamite around the vessel, blasting the thick sea ice that enclosed them to create a narrow path to freedom. All but two of the crew survived the ordeal.

But now, for large parts of the year, the once plentiful sea ice encountered by the ill-fated voyage seems to be disappearing.

To discuss the expedition's history; the importance of Antarctica's sea ice in regulating the global climate; and the planetary implications of its growing absence, Live Science sat down with University of Tasmania oceanographer and climate scientist Edward Doddridge, who uses mathematical models and observations to understand the dynamics of the region.

Here's what he had to say:

Ben Turner: What was the voyage of the RV Belgica? And how did it contribute to our understanding of Antarctica?

Edward Doddridge: The RV Belgica's voyage to Antarctica departed in 1897 and was the first of what became known as the "heroic age" of Antarctic exploration. This was the very end of the 19th century and the beginning of the 20th. Antarctica was a completely unknown place that no one had been to. Then — within just over a decade — people had gone all the way to the South Pole. 

Our scientific understanding of the region blossomed as we obtained the first records from the continent. It's still a continent that teaches us so much today, but the RV Belgica's voyage is the start.

BT: One of the reasons why you've written about the Belgica, and why its voyage is so famous, is because the pack ice there was so thick that the ship became stuck for nearly two winters. What does this tell us about that part of how the Antarctic was like back then? And how has it changed since?

ED: This is why I think that the RV Belgica's voyage is such an interesting one to look at now. The region of the Antarctic coastline they sailed to has been ice-free for the first time since satellite records began — it now doesn't have any ice for months and months of the year. That's pretty surprising in a 45-year record, but when you look back 125 years ago, and you see that they were trapped in ice that was 2 meters [6.6 feet] thick, that's a huge change.

It's a really startling story, because it's a nugget we can use to understand how it's changed over the last century. If you were to go down there this summer in a boat like a Belgica, you could sail all the way to the Antarctic coastline, frolic around on the Antarctic shore and then sail back to Belgium. And you might not have seen any expansive sea ice.

BT: Bringing this closer to the present — in 2023, after several years of record lows, the sea ice over the Antarctic's winter period failed to regrow. By the end of the Antarctic winter in July, the continent was missing a region of ice bigger than Western Europe. 

You're a polar researcher, you've studied this for a very long time. What were your thoughts when this happened last year?

ED: Almost disbelief. The measurements that we get for Antarctic sea ice are extremely well-calibrated, we know that the satellite is truthfully telling us how much ice there is. But looking at that graph, it was hard to comprehend that it could be so different from previous years. 

As a research community, we've struggled to even describe how unusual the change is. People throw around words like "unprecedented" or "gobsmacked" or "'unbelievable." For a while we were trying to use statistics to say that it was a one in many thousands or millions of years event; then we got into billions and even into tens of billions of years. 

At some point along the way, you just have to realize that the statistics aren't useful to understand this anymore. It's so far outside what we've seen in the last 45 years that we just have to say that it's completely different — that's as good as you can do.

BT: Yet even a non-expert in the field, who doesn't know about the different dynamics between the Arctic and Antarctic and is just generally aware of climate change as a thing, might expect this ice to melt at some point. Why did it surprise you so much?

ED: The difference is that the Arctic is an ocean surrounded by continents, whereas the Antarctic is a continent surrounded by ocean. So in the Arctic, the amount of ice that you have in the winter is basically just the amount of ocean that you have, but you're never going to run out of ocean around Antarctica.

So when sea ice forms around Antarctica it can expand a long way, and the limit of this expansion is set by the interaction between the ocean, the atmosphere, and the ice. This means the ocean currents around Antarctica are crucial for how much ice you can have. All of this makes it really difficult to model. 

In the past, The [Intergovernmental Panel on Climate Change] IPCC models suggested that we should be losing ice in the Antarctic, just like we are in the Arctic, but we didn't see that in the satellite data up until 2014.

So last year, when it didn't come back during the winter, it was something that we hadn't predicted. We had the sense that climate change meant we will get less ice at some point in the future. But if you had asked climate scientists in 2020: "What's gonna happen in the winter of 2023?" No one would have predicted what we saw.

BT: So what's going on in the Antarctic to cause it? 

ED: Fundamentally, it has to be that the world is getting warmer and we know that a warmer world isn't consistent with lots of sea ice. As the atmosphere and the ocean warm, they're both going to affect the sea ice. But understanding all of the nuances of those interactions is really quite tricky.

There's a layer at the top of the ocean called the mixed layer. It has the same properties at any given location — it doesn't really change in temperature or saltiness. Around Antarctica, that layer is mostly about 100 meters [330 feet] thick during winter. Below that is where warmth comes up from other parts of the ocean and mixes with the top layer where it can inhibit sea ice. We've shown in our research that those subsurface ocean temperatures have been increasing, and the places where they've warmed the most we see the greatest reductions in sea ice.

BT: Playing devil's advocate, how can we rule out for certain that this is some kind of freak event? How do we find the smoking gun of a climate change signal in all of this?

ED: The honest answer at the moment is that we can't — we cannot conclusively rule out that this is just under multi-decadal or centennial variation in the sea ice. What we can do, though, is we can look at the 45 years of data that we have [satellite surveys of the poles began in 1979]. This suggests that, if there is some kind of change or freak event, it doesn't happen in a 45-year timeframe. 

The other thing that we can do is we can use models and run them over thousands of years. Again, there's no indication that something like 2023 regularly happens at random in these models.

BT: The Antarctic is one of the most remote regions of the world. Why does a sudden decline in sea ice there matter globally?

ED: So there are a few really crucial things that the sea ice does within the climate system. Firstly, it's really white and bright, so it reflects the sun's rays back out into space. This insulates the ocean underneath it and keeps it cold. If you take that away, you're accelerating the rate of warming in the region and contributing to increased warming globally.

Secondly, tiny microscopic plants called phytoplankton that absorb CO2 in the atmosphere grow on the sea ice, and there are also regions that form around the ice that take CO2 out of the atmosphere and away from the surface — roughly 10% of carbon dioxide that humans have emitted has been absorbed by the Southern Ocean. 

Finally, on a human level, so many really iconic species live around Antarctica. Krill feed on the phytoplankton that grow on the ice. So if we take it away, the krill will suffer, and so will the entire Southern Ocean ecosystem. 

BT: If the sea ice continues in its current decline, where could it end up?

ED: The best tools we have are the models. And if you run them for long enough, then yeah, you reduce the amount of ice around Antarctica substantially. The other way we could guess is by looking at geographic sediment core records for past climate epochs. 

From those you can find periods where Antarctica had trees and plants and all sorts of animals living on it, suggesting that it was not a frozen continent. So you can certainly warm the planet up enough that there is no ice left, although I very much hope that we don't get anywhere near that.

BT: That sounds pretty disastrous for coastal regions, how much would sea levels rise if all that ice melted?

ED: Antarctica contains enough ice to raise global sea levels by 60 meters [200 feet].

BT: The Antarctic's circumpolar current drives the thermohaline circulation and global ocean currents such as Atlantic Meridional Overturning Circulation (AMOC), which are really important for regulating Atlantic climates. Could this melt affect them?

ED: Changes in the sea ice are definitely going to impact the AMOC. The AMOC has water that forms up in the North Atlantic, it gets cold and salty and it sinks down and then comes back up in Antarctica. And there's another loop to that circulation for the cold dense water that forms around Antarctica.

That formation of what we call Antarctic bottom water — the densest, coldest water in the global ocean — is really dependent on sea ice formation. When glaciers and ice sheets on Antarctica melt, they release fresh water into the ocean and reduce the salt in the surface waters. 

This means they can't get as dense and sink as easily, reducing the rate of the circulation. There's been a couple of papers that have suggested that the AMOC has slowed down by 30% in the last few decades, and that there could be up to a 50% decrease in the coming years. 

So absolutely — changes in sea ice around Antarctica will change the global overturning circulation and the distribution of heat, salt and nutrients that it carries with it.

BT: So even though we can only see the first few dominoes in the chain, what we could be seeing is the start of a fundamental shift in the way our planet regulates temperature.

ED: Absolutely. It sounds kind of grandiose to say that, but it's true. The Southern Ocean around Antarctica is the center of our global ocean. It's where the Pacific, the Atlantic, and the Indian oceans meet. So changes that happen in the Southern Ocean impact all of the oceans around the world. And if it changes, it alters the climate everywhere.

BT: And what should we be doing more broadly?

ED: Fundamentally, the only thing we can do to reduce the magnitude of these changes is to emit less CO2. That's the only lever we can pull. The only knob we can turn is how much CO2 we put into the atmosphere.

Editor's Note: This interview has been edited and condensed for clarity.