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the melting monster of sea level rise – The Conversation Weekly podcast transcript

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This is a transcript of The Conversation Weekly podcast episode: Thwaites Glacier: the melting, Antarctic monster of sea level rise, published on September 22, 2022.

NOTE: Transcripts may contain errors. Please check the corresponding audio before quoting in print.

Dan: Hello. I’m Dan Merino in San Francisco.

Gemma: And I’m Gemma Ware in London. Welcome to The Conversation Weekly.

Dan: This episode, we’re headed to Antarctica.

Yixi Zheng: Everything’s very, very surreal in Antarctica. So it’s really a land full of magic.

Dan: This is Yixi Zheng. She’s a PhD researcher in physical oceanography at the University of East Anglia in the UK. In January of this year, in the middle of the Antarctic summer, she set off on a research cruise to go as far south as you can go. She went to the waters of the Amundsen Sea off the Antarctic coast.

Yixi: This region, normally it could be covered by sea ice ten months a year, which means it only gives us about two months a year to enter this region.

Dan: Yixi uses seals to collect data on what’s happening in the water underneath the region’s giant ice sheets. To do this, her team needs to fix electronic tags to the heads of these seals before they go diving out under the ice. Yixi and her colleagues were looking for two species of seals: elephant seals, those giant loud seals with long bulbous noses, and Weddell seals, which are quite a bit smaller, quite a bit rounder and quite a bit cuter actually, too.

Yixi: For elephant seals, we normally try to find rocky islands and then we went into a small boat, we called it zodiac. And from that small boat, we can go to the rocky islands and then we try to tranquillise the seal and then tag the seal.

Dan: Yixi wasn’t actually tagging the seals herself. There was a marine biologist to help her do it. And while the elephant seals are normally on land, the Weddell seals live out on the ice flows, these huge sheets of floating ice in the Amundsen Sea.

Yixi: That time we just went to the zodiac, and then from the zodiac, we went to the ice floe, and just repeat the same thing. We tranquillise the seal and then we can tag them. Normally the wind is really fierce, so we kind of can’t hear anything because the wind was so strong. But if the wind goes down a little bit, we can hear the sound, the sound of the ice cracking when we put our feet on the top of the ice float. And sometimes when we tranquillise the seals, we can hear them snoring as well.

We need to stay with the seal for a while to check whether they are breathing properly and check whether they are still behaving normally. So after we tag them, we will stay, try to monitor the seal and listen to their snoring or just their quiet breathing.

Dan: So you tag these seals, then what happens?

Yixi: Yeah, so the seals that we tag, they can go to somewhere near the seabed for food, and then when they rise up, they will try to find the shortest way, which means that we can get a vertical profile of the water property in every dive that they have.

Dan: Because the seals take a vertical path up to the surface, they act as almost perfect water sampling devices. The tags measure salinity and temperature of the water, among a few other things. But those two pieces of information are basically all you need to tell what kind of water the seal is swimming through. The water in the ocean near Antarctica is an interesting mix of actually different types of water. There’s water of various temperatures and levels of saltiness, all forming layers and swirls and complicated patterns. It’s like a cup of water after you drop some food colouring in it. And one of these types of water that gets swirled into the Antarctic ocean is particularly important: the water melting from the region’s glaciers

Yixi: It’s a very special region, because the Amundsen Sea is surrounded by some of the most rapidly melting glaciers in the world.

Dan: Yixi was telling me about what it felt like to stand on the bridge of the research ship, looking out through the big glass windows over the sea, towards the glaciers. She said the scale of what’s happening really hits home.

Yixi: We know that the glaciers in Antarctica are melting, but like when you can really see the icebergs and when sometimes you can really see the glaciers and they are melting, you can see the water dripping from the glaciers. And we get really emotional, when we saw those glaciers, they were pretty much crying.

It’s so strange when you see those things, because you normally just study it in textbooks and we even write papers about it. But when you see them with your own eyes, everything just changed. For me, it’s even like a motivation booster that forced me to do more work about Antarctica research.

Dan: One of these rapidly melting glaciers is of particular importance to not only scientists, but everyone on earth. This is the Thwaites Glacier.

Gemma: So Dan I’m I’m feeling that what was a quite fun story about seals is turning into a pretty sad story about climate change.

Dan: OK. So that feeling right, Gemma, that kind of resigned, “Oh gosh, another awful climate change story,” I feel that. I empathise with that, and I often understand and am in that same head space. But sometimes you learn about a very specific place, a very specific symptom of climate change, and it is dramatic and terrifying and stops me in my tracks. And that is the case with the Thwaites Glacier.

Gemma: So why is the Thwaites Glacier at this moment for you?

Dan: Well, in talking to the experts we’ve interviewed for the episode, I came to understand how this singular glacier, which is very big, how this individual chunk of ice is going to dramatically change the face of the earth. This one glacier is going to raise sea level. The Thwaites Glacier is going to make the lives of hundreds of millions of people, and if not the whole globe, more difficult.

Gemma: So I’ve heard that, you know, there are glaciers all over the world, like in the Arctic, in Greenland that are melting. So why is Thwaites so different? What makes it so special?

Dan: Well, it has to do with the topography of the actual continent of Antarctica that Thwaites sits on top of.

Ted Scambos: It’s a giant white sheet of ice. The scale, I think really impresses people when they go down there, because everybody suffers from this sort of misconception, because Antarctica is usually a tiny little spot on the bottom of the map. Sometimes there’s a lot of maps that don’t even include Antarctica. So you think of it as being smaller, you just don’t grasp that it’s as large as North America and Mexico combined.

Dan: This is Ted Scambos. He’s a senior research scientist at the University of Colorado in Boulder, in the US. And he’s the US lead for a big international research collaboration studying the Thwaites Glacier. But before we get to the glacier, let’s start with the actual land of Antarctica itself.

Ted: The earth has gradually gotten cooler over the last several million years, until very recently. And, uh, as that happened, an ice sheet slowly accumulated over the continent that was Antarctica. And that’s what we’ve got today. It’s several islands and a continent, a large island that looks about like Australia.

Dan: The large Australia-shaped part of the continent is called east Antarctica. It’s roughly south of Australia itself. On this side, the ice sheet is sitting on top of a giant mountain range and some relatively higher land. But if you head west of the mountain range, the land drops off, super quick.

And there’s even a huge basin that drops down to more than a thousand meters or a few thousand feet below sea level. But it’s not filled with water, it’s filled with ice that goes from above sea level all the way down to where the land and the continent actually is. If you keep going farther west, the land rises back up again, and there’s some islands that stick out and the ice sheet is thinner there connecting all these islands and stitching them all together.

Ted: So flying over it, it’s incredibly flat, until you get to an exposed rock mountain outcrop, which are, they tend to be steep and very sharply cut. But then underneath, of course, there’s this huge landscape, that’s mostly continental rock. Although there’s some areas where this thick ice sheet is covering the ocean, the sea bed. And that’s because the climate is so cold that the ice is built up to the point where the bottom of the ice has actually gone down into the ocean and it’s resting, firmly, on the seabed that would be a few thousand feet below sea-level. It’s covered by ice. So that actually makes for an unstable situation in terms of how the ice sheet’s going to evolve in the future, and that’s a big part of why we’re studying this particular part of Antarctica that we’re working on.

Gemma: So I’m still trying to imagine what this looks like. You’ve just got loads of ice, but it’s below sea level.

Dan: Yeah. It’s super confusing, right? So imagine you’ve got a big wide dish full of just a little bit of water and you have a giant block of ice and you put it in that dish. It’s not gonna float on that little bit of water. It’s gonna sink and touch the bottom of the dish. So the ice is both above sea level and below sea level and touching the bottom. That’s pretty similar to what’s happening in Antarctica and on the Thwaites Glacier.

Gemma: So why are scientists so concerned about this particular glacier, this Thwaites Glacier?

Dan: Because Thwaites holds so much ice and it’s melting for some very particular reasons. And if scientists understand why and how, we’re gonna have a really good idea of how much sea level rise the entire world is gonna face in the future.

Ted: It’s actually the widest glacier on Earth. It’s nearly 70 miles across from one side to the other, and then it reaches into the continent, but in a very broad way. It’s really not like a glacier. I mean, even flying over it, you don’t really get the sense that, “Oh, I’m flying over a glacier and there’s one end and there’s the other end.” You’re flying for hours and it’s the same glacier and you get to the coast and there’s all of this broken up ice and stuff. It’s all one thing, Thwaites Glacier, and that’s really impressive. It also kind of underscores, this is a patch of ice, that’s actually big enough all by itself to have a significant impact on global sea level, which of course is a huge volume of water that we’re talking about.

Dan: To understand what’s really at stake as Thwaites Glacier melts, you have to understand how it’s structured and there are three main parts to it. There’s the big basin of west Antarctica that’s way below sea level and filled with a mile of ice. The next part is this narrower, shallower layer of ice that extends out from the basin, west, and still goes down to the seafloor and that connects to a floating ice shelf that juts out over the Amundsen Sea.

Ted: When the glacier first arrives at what you could call the coast, the point where it goes afloat, that’s not like a beach. That is underwater by several hundred meters, but still that deep ocean water is warm. I say warm it’s like three or four degrees above, freezing. So, you know Thwaites is like your ice cube inside your cocktail, and the ice cube just starts to disappear pretty fast for sure. So in the course of a year, you lose metres, tens of feet of ice from the base of the ice sheet. And because that ocean water is swirling past the front of Thwaites Glacier more often than it used to, you’re seeing this gradual retreat.

Gemma: So it’s like the ocean where it touches this floating ice sheet is kind of eating away at it, eroding it from below?

Dan: Exactly. That’s exactly right, Gemma. And you’ve got this big floating ice sheet, that’s way out west. The ocean water’s melting slowly from below, but that’s happening with a lot of glaciers. It’s the structure of Thwaites. Remember there’s the ice sheet, but then there’s also this kind of narrower connecting bit that connects the ice sheet to the big giant ice-filled basin: that’s what’s really important. And that’s why people are worried about Thwaites.

Ted: The problem with Thwaites is that there really is just a big wide gap that leads directly to the deepest part of that ice-covered seabed.

Read more:
Ice world: Antarctica’s riskiest glacier is under assault from below and losing its grip

Dan: The gap is the middle of the three parts. It’s filled with relatively shallow ice. On one side, it’s melting, it’s the ice sheet. On the other side, the giant ice-filled basin

Ted: As the point where Thwaites glacier ice goes afloat moves back into the centre of west Antarctica, the bedrock sort of falls away, deeper and deeper, so the actual ice that’s remaining is thicker. It’s being eroded at the base by warm water, and so when you’ve got a bigger pile of ice further in the interior it wants to squish out even faster. So you can get a runaway situation where as you begin to step back from this gate area that’s next to what’s now the ocean, you begin to accelerate the ice flow and you get a runaway where the ice flows faster, but then it thins faster, but then it hits this thicker ice in the centre and flows out more rapidly.

Dan: So where are we with this melting process? What’s the status right now? What are we looking at in the coming years?

Ted: The section that is moving fast is maybe oh, 20 miles or so across, and the other parts of it are partially blocked by a section of the ice that’s actually hit some islands offshore. So it’s kind of holding back the ice a little bit. Now, what we’ve been studying lately is that that part is breaking up. In fact, in the near future, like five to ten years from now, it’s likely to be gone. So then that’s gonna lead to more widening of the glacier.

Dan: Once the glacier melts all the way back into the basin, you get warmer, ocean, water touching, and therefore melting so much more ice because the basin is giant and super deep.

Ted: We’re talking about an area that’s the size of the island of Great Britain with a mile of ice to give to the ocean. So you pick up a mile of Great Britain and you plop it into the ocean, you’re gonna see some sea level rise. And that’s exactly what we’re worried about from Thwaites, that there’ll be an increase in the rate of sea level rise between now and the end of this century, and especially into the 2100 to 2200 period.

And if we’re lucky and we slow down on global climate change, we can extend that out to a few millennia. I’m not sure if anybody’s willing to say we can stop it, that would require a turnaround that’s kind of hard to imagine, but we can get the pace of sea level rise from this glacier, and from a lot of other glaciers around the world, to stretch way, way out so that we’re able to manage it.

Dan: So Ted, you say that the floating ice sheet’s gonna melt in the next five to ten years, but that’s not actually gonna add much sea level rise because it’s already floating in the ocean. But as the melting steps back inland, how much sea level rise are we gonna see from Thwaites?

Ted: Yeah. So right now Thwaites contributes about 4% of the total global sea level rise. So sea level has been increasing for centuries and it’s taken a big uptick in the last 50 years or so, where it used to be about a millimetre and a half per year, and now it’s more like three and a half millimetres per year. Between now and the end of the century, we’re expecting that Thwaites will contribute several centimetres to sea level rise. But, at the end of the century, the pace of sea level rise that’s being contributed by Thwaites will be fairly high, a bigger fraction than 4%. And as you go forward into the next century, 2100 to 2200, you’re gonna see that be a bigger and bigger fraction.

Dan: Thwaites is part of a large system of interconnected glaciers and ice shelves in west Antarctica. These include the Pine Island Glacier and Dotson Ice Shelf. And Thwaites kind of acts like a plug. Once Thwaites retreats, all the way back into the big basin in west Antarctica and that ice starts melting, the rest of the ice that surrounds Thwaites, these are those other interconnected ice sheets, are all going to beging to flow into the big basin and also start melting. Ted told me that there are 60cm, or just about two feet of sea level rise locked up inside Thwaites itself. But if sometime, many hundreds of years in the future, the entire west Antarctic ice system that Thwaites is central to melts completely, we’re talking about three metres or ten feet of sea level rise.

Ted: It’s a slow start. It may not sound like much, but right now we already are concerned with the rate of sea level rise and it’s only three and a half millimetres. By the end of the century, the values that people are talking about are 6mm to 30mm, if things really get underway in Greenland and Antarctica. Those sorts of rates make it really difficult for anybody who’s trying to manage a port or a landscape that’s near the coast, how to defend that or how to prevent the high tides or the storm surges that are really destructive.

We’re already seeing those, and yet, if we have rates of sea level that are ten times greater than today, then everything you build in the year 2090 is gonna be obsolete by the year 2100. And so you’re constantly throwing billions of dollars trying to protect places like New Orleans or Miami or Bangladesh or Amsterdam, and you really drive the economy downhill. This is a trillion dollar problem in the future, but we might be able to address it with well spent tens of billions right now.

Dan: I just wanna kind of reiterate something you said there, just so people understand what we’re talking about. When you said 30mm, you’re talking about a yearly rate of sea level rise, right?

Ted: Yes, in one year, yes.

Dan: That’s astounding.

Ted: Yes, that’s what I’m trying to tell you.

Dan: Yeah, I know. And I just don’t think people understand that it’s the rate … your point excellent. Right? When we have a constantly rising sea level, it’s not like it just goes up and we address it and get used to that new one. The sea ice is rising, not, it has risen and rose and it stopped. So, I just think that, you know, you’re talking about really this whole concept of Thwaites is about an accelerating flow of ice into the ocean. And it’s this rate, that’s this big idea here.

Ted: Absolutely, and I’m glad you’re emphasising that, because that is a big problem. People talk a lot about what’s the state of the world in the year 2100 and in any one of a number of dimensions, it doesn’t stop in the year 2100. It’s not like, “Oh, I can handle a metre of sea level rise.” No, no, no. The problem is that at 2100, it’s not just at a metre, it’s also going up at a very fast rate so that the next century is really difficult to deal with. And, and that gets into the moral debt that we owe the future that I think is really ultimately the driving reason to take this, and take this on seriously.

Dan: Some people call Thwaites the “doomsday glacier”. Do you like that phrasing that nickname? And if so, why? If not, why not?

Ted: Well, so there’s good and bad. “Doomsday glacier” is certainly … people remember when they hear it. And, they may not know much about Antarctica, but they’re slowly becoming aware that there’s a section of Antarctica that is really a problem. The thing I don’t like about the doomsday label for the glacier is that it gives the impression that first of all, there’s nothing we can do about it. And secondly, that it’s going to unfold very quickly, like a nuclear attack or something, we’re suddenly going to see a destructive force emerge from Antarctica.

But more importantly, it’s not impossible to address this problem. Model after model shows that if we really turn down the heat and allow things to get back to where they were in past decades, then the processes that drives this melting and this flow of the ocean that’s bringing warm water up to Thwaites, that also will slow down.

Gemma: Dan, you know, I totally get what Ted is saying there about the doomsday glacier. I understand why a scientist might not wanna call it that because it gives us this label that you, something you can’t do anything about. But that’s where they’re trying to understand it. Right? They’re trying to understand the processes, that are causing this glacier to melt more quickly now than it has been. So what’s going on or what, what are they finding?

Dan: Well, this is actually a tricky question that a lot of scientists are working on. And one person who’s really summarising all the data and trying to understand the mechanisms at play, that are really causing this melting, is a guy by the name of Paul Holland.

Paul Holland: Most of the ice loss is happening in the Amundsen Sea, which is where Thwaites Glacier is. And in that region, the ice is really not melted by the atmosphere, it’s all melted by the ocean. So we know if something’s changing in that region, we know it must have been the ocean that caused this change.

Dan: Paul is an ice and ocean scientist, and he works with the British Antarctic Survey, which is based in Cambridge, in the UK.

Paul: I’ve been studying the ocean for years and years. And we know that in that region, there’s this very warm water. Very warm water by Antarctic standards is plus one degree celsius. Right, so it’s one degree celsius water, which we regard as ridiculously hot and that’s melting the ice.

Dan: So the big question right now is why is the warm water there and why is there more of it than there has been in the past?

Paul: And where we’ve got to with that question is over the last 20 years or we know that the changes in that warm water are caused by the winds.

Dan: So winds are what control how ocean water moves. It’s why waves are created. It’s why there’s ocean currents. It’s all wind. So Antarctica is a circle, roughly the continent. The winds down there generally just go around the continent in a circle from west to east. But the Amundsen Sea is unique because it’s affected by tropical wind patterns in the Southern Pacific Ocean, which have a lot of natural variability. These are things like El Niño and La Niña. And so Paul told me that it’s the combination of these two things, the winds that are constantly circling around Antarctica as well as winds from the Pacific that affect how the warm water moves, down near Thwaites. Another important aspect of the Amundsen Sea is that it’s relatively shallow, but right next to a very deep part of the ocean and in Antarctica, deep ocean water is much warmer than the surface water.

Paul: It’s a huge reservoir of heat. So the question is: how does that warm water get to the ice and start doing some melting? And what we think is going on is that the wind blowing on the ocean has kind of changed its location and speed. And this has caused that warm water to flow into the Amundsen Sea, onto the shallow bit, and therefore go underneath the ice and start melting it.

So, I guess, our best hypothesis is that over the last hundred years, that changed. The direction and speed of those ocean currents changed. Now, the problem we have is in the Amundsen Sea, the first ship ever went there in 1994. So we have no observations at all before 1994. And this is why oceanographers like me, abandon oceanography at this point and have to start looking at winds, because we know a lot more about the winds over the last hundred years.

Gemma: Dan, if nobody really went down to this area of Antarctica much before the 1990s, then they weren’t really taking any kind of wind readings, I imagine. So how did they know what was actually happening? Like what the wind speed was doing and what direction it was coming from?

Dan: So there’s a couple ways you can do this and scientists do all this stuff. First, models. You can plug all the data we have about times before the 1990s and use computer models to simulate what was likely happening in the past. Another way to actually get direct data is to use an ice cores.

Gemma: So this is where they drill down into the ice and try to figure out what happened in the past?

Dan: Yeah, exactly. And in this case, they’re looking for sediments and dust and particles and anything that the wind carried in over the last hundred years.

Gemma: And what do they do when they find that?

Dan: Well, people like Paul will take that information and plug it into their climate models and use that to basically get a pretty good sense of what the winds were doing in the past.

Paul: So we’re interested in a particular area where the ocean goes from being deep to being shallow. So that’s called the shelf break, the edge of the shelf. And that’s where, if you get the warm water onto the shelf, it’s then on and it’s going to melt the ice. And at the moment, the wind in that region of the Amundsen sea, it blows in one direction towards the east for a few years, then it reverses and blows towards the west for a few years and so on. And it kind of wobbles around. So the variability is the story, there is no average wind. It’s all about the variability.

And what we know is that when it blows towards the east, that redirects the ocean current and brings warm water onto the shelf, and so we get an increase in ice sheet melting. And when it blows towards the west, that reduces the flow of warm water onto the shelf. And we can see this in the satellite records of the ice sheet thinning, we can actually see that when the wind reverses, the ice sheet kind of slow down, and then when it flips back, it speeds up thinning again. So we know for sure that the ice is responding to this wind variability. And that’s the logic I use to, to then study the winds in the past and the future.

Dan: I want to kind of start digging back through history now. You’ve written about the fact that there was an interesting shift in the wind patterns around world war two. Can you explain what that was?

Paul: So, we know from ice cores that something unusual happened, starting in about 1940 and lasting a few years. And it was a big wind anomaly. And it did have a big effect on west Antarctica, and we know this because, you know, the ice cores have recorded this. But it doesn’t seem to have been a standard pattern of natural variabilities.

Dan: This was a weird anomaly in the winds. It happened during world war two and lasted for an unusually long amount of time. That’s what made it so special. And it was really important for the ice sheet down in Antarctica.

Paul: Because, if you slosh some warm water onto the shelf, and then you slosh it off again a year later, the ice sheet, you know, the ice sheet’s very slow and sluggish and it’s not really gonna care about a one year anomaly. But if you slosh it on and keep it there for five years, that gives the ice time to be melted away and a larger amount of ice is lost. And then that can really perturb the ice.

So what we think is it looked a bit like a normal bit of tropical variability, but with an unusually long assistance, and that we think was enough to destabilise the ice sheet. That prior to that event, it had been sitting in its position for thousands of years, and we know for a fact on one particular glacier, Pine Island Glacier, my colleagues have drilled through the ice and collected sediment cores from beneath the floating ice, and they can show from the sediment calls that the ice was sitting there very happily until 1940, 1945. That’s when the modern retreat began for that glacier.

Dan: You said that this was the trigger of instability. Do you mean like instability up till today, as well, or did this, you know, after the five years it started to grow back and it reached another stable state?

Paul: We don’t know for sure. So we know that there was some kind of retreat ongoing between 1945 and 1970. After 1970, our satellites start to switch on. And ever since the beginning of these satellite observations, there’s been signs that these glaciers have been retreating. So as far as we can tell, the ice was stable for 10,000 years, something happened in the forties, it slowly started to retreat, and then ever since then, the retreat has gone up and up and through the roof. And now we’re observing it in ridiculously fine detail with satellites. So we know that the kind of retreats we’re seeing now must have been unprecedented.

Dan: So Paul, you just explained how this anomaly occurred around 1940, but that’s before humans were driving a lot of climate change on Earth. There just wasn’t a lot of greenhouse gases in the atmosphere at that point. But a lot of the melting of Thwaites is connected to climate change. So how do we resolve that seeming contradiction? Like, I feel like we have to ask that question, right?

Paul: Yeah, absolutely. I mean, you know I’m open to all ideas. I mean, we know the natural variability is extremely strong in this region. So that’s why I went into this work with an open mind about what we were gonna find. When we looked at the winds in these climate models they only started feeling greenhouse gases in the 1950s and 60s. And they only feel the ozone hole opening up in the 80s. So there was nothing in the 40s that could have, at least to my knowledge, that’s human caused, that could have triggered these retreats.

So, we’re left with this paradox, right? People have always said, “We turn on satellites, we see all this ice retreating, you know, there’s gotta be a relationship. Humans, humans must of caused this, right? It shouldn’t be retreating otherwise.” But there’s always been this conundrum. So I think the way we resolve this in this latest work, and this is a sort of discussion point for future studies, more than a concrete conclusion, we feel that the retreat was triggered naturally, but that the ice sheet probably should have recovered. So that it’s possible that several of these mini-retreats have happened over the last 10,000 years, but the difference with this one was that when the ice should have been regrowing, you know, greenhouse gases first start to have an influence. And that was just enough to stop the ice from re-grounding and re-stabilising itself.

Dan: So what Paul’s saying here, and we should note that it’s not peer reviewed or published yet, is that it’s not one situation or the other it’s both. A naturally occurring pattern triggered the initial wind anomaly, but humanities impact on the planet is the reason these winds have kept blowing and are actually getting stronger.

Paul: So with the natural variability, we know there was this big event in the 1940s. It was part of a sort of longer period, a sort of 20 year period of slightly anomalous winds. So that happened. And then sort of in the 1960s, the wind changes due to greenhouse gases started, slowly at first, but have built ever since then, with the continued emission of greenhouse gases. But then there was a big jump in the late 70s through the 80s when the ozone hole opened. So the opening of the ozone hole had almost exactly the same effect as greenhouse gases. It increased these westerly winds that are going all the way around Antarctica, west to east. And in fact, over that, over that sort of ten-year period, the ozone hole opening up had the same strength of effect as all of greenhouse gases over the 20th century. So it was a really strong acceleration in the winds.

Dan: So Paul’s hypothesis is that if there hadn’t been any climate change, you would’ve had the ice shrinking in the 40s and growing back in the 60s and 70s, and then shrinking again in the 90s and this kind of natural back and forth that is natural variability. But the problem is that in the 1960s, climate change really started to affect the winds, and this began to overpower the natural variability.

Paul: So basically in the 90s, we have this like perfect storm where the ozone hole is fully open, greenhouse gases have gone through the roof at this point, and the natural variability has gone back to sort of 1940-ish. So I think that is the combination of those three things that’s causing the rapid accelerations we now see. But the problem is we still don’t know in precisely what combination, those three things were acting.

Gemma: So Dan, it’s like Paul is looking back in history. He’s kind of a detective looking back at these wind patterns to understand what happened, but actually this is all trying to understand the future and what’s gonna happen next, right?

Dan: You’re absolutely right, Gemma. But if you wanna understand what’s gonna happen in the future with Thwaites, remember this is about glaciers, you need to understand the wind patterns and the mechanisms of this really complicated system in the past, otherwise, how are we gonna know what’s going on in the future.

Gemma: This is fundamentally about sea level rise and what’s gonna happen over the next couple of hundred years, isn’t it?

Dan: Yeah, it’s sea level. That’s why people like Paul and Ted and Yixi and everyone are down there studying Thwaites. And the important thing they’re trying to look at, especially Paul, is how much of this sea level rise is really due to human activities.

Paul: So we know the ozone hole is stabilised and is gonna close up. So that’s gonna give us a real help. We know that change in the wind is gonna reverse over the coming century, the present century. So that’s good. But we still have greenhouse gases to work on. So the question is, if we reverse these greenhouse gas-induced, wind changes, what effect does that have on the ocean and therefore the ice melting? And once we’ve achieved that what’s gonna happen to the ice sheet, will it regrow? Or will it take, you know, many centuries to stabilise and then it might regrow? And my guess would be that the second one is the more likely.

Of course, that’s only talking about the human part. Of course, there’s this also very strong natural variability over which, you know, not only we have no control, but also it’s impossible to predict. So in fact, we can’t predict the sea level from this region, because of the strong role of natural variability. All we can do is say here’s the range of possible outcomes. So I think all these questions have got immediate policy impacts over the mitigation of greenhouse gas emissions, adaptation to the sea level rise, that may or may not come.

Gemma: I like Paul’s honesty here, Dan, about what they’re not really sure about yet, about how bad, I guess, it’s gonna get from Thwaites.

Dan: And it’s two pieces of uncertainty, right? We don’t know how bad it’s gonna get. And we also don’t really know just how much human actions, reducing greenhouse gas emissions, will influence this system. It might be that we’ve tipped a domino and it’s gonna keep going, or maybe we could slow it down.

Gemma: And I guess that’s why they just keep going down there every season to try and find out more data and plug it into those models and get some answers to all that.

Dan: Absolutely. We’re all gonna hopefully try and reduce our greenhouse gas emissions, but having a better idea of what’s really gonna happen in the future is super important. And that’s why people like Yixi, and we’re about to go hear about the seals again, are still down there.

So it’s currently winter in Antarctica. Are you getting data from your seals right now? Like, are you still getting stuff from your research subjects? You research assistants I should say?

Yixi: Our part-time workers.

Dan: Yeah, there you go.

Yixi: So yeah, they are still taking a very lovely winter holiday. So we are still getting a lot of data from them.

Dan: The 2022 research cruises down to the Amundsen Sea weren’t actually able to reach the Thwaites Glacier. A couple of icebreakers, including ships from China, Korea and the UK, tried to get through, but they couldn’t. The sea ice was super thick last year.

Yixi: And we tried so hard to break the sea ice and then tried to go into somewhere near Thwaites, but we couldn’t. But the seals that we tagged, they went in front of Thwaites.

Dan: This year’s seals, though, are still out there collecting data. Thank you to all the seal volunteers. But Yixi and her colleagues have been analysing data from seals tagged in the last few years. And, with all this data that they’re collecting, they’re gonna be feeding it to people like Paul and Ted and everyone else out there working on Thwaites.

I want to give the last word to Ted here because during our conversation, he said something that was really powerful, at least to me, explaining how, though we’re not certain just how much changing human behaviour can slow down this melting, we do know it will slow down melting and that’s really important.

Ted: I’m not sure anybody’s prepared to say that we can actually stop this or regrowth Thwaites Glacier in anything like human imagination timescales, several thousand years. But we can slow it down. And it’s imperative that we do so if we give a damn about our grandkids. People really will inherit a planet that’s fundamentally difficult to live on in the future if we don’t do things right now. They won’t have a magic bullet that says, “Nope, we’re putting all the glaciers back in place and we’re lowering sea level.” It’s not gonna happen. It’s up to us to do that now. We saw that we can eliminate whole species. We saw that we can eliminate whole ecosystems. We saw how important wetlands are. Now we’re seeing how important global climate is and the ice sheets are. and that’s I think a motivating force for taking action now.

Dan: OK, that is it for this episode. We’ve got a few people to thank. First, our colleagues, Stacy Morford, who worked with Ted Scambos on his original story for The Conversation. Thanks to Joanne Johnson at the British Antarctic Survey, as well as Sharon Stammerjohn at the University of Colorado at Boulder for their help with the episode too.

Gemma: A final, thanks to our global executive editor, Stephen Khan, to Alice Mason for our social media and to Soraya Nandy for help with our transcripts. And to Graham Griffith for all his help over the last few months.

Dan: You can find us Twitter @TC_audio; on Instagram; or via email. You can also sign up for our free newsletter, just click the link of the show notes and it’s actually good newsletter, and it’s actually a good newsletter, I promise. If you like what we do, please support our podcast and the conversation more broadly by going to donate.theconversation.com

Gemma: The Conversation Weekly is produced by Mend Mariwany and me, Gemma Ware, with sound design by Eloise Stevens our theme music is by Neeta Sarl.

Dan: I’m Dan Merino. Thank you so much for listening.

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