Thwaites Glacier, photos by Jeff Goodell

The Fuse Has Been Blown and the Doomsday Glacier Is Coming for Us All
by   /  December 29, 2021

“One thing that’s hard to grasp about the climate crisis is that big changes can happen fast. In 2019, I was aboard the Nathaniel B. Palmer, a 308-foot-long scientific research vessel, cruising in front of the Thwaites Glacier in Antarctica. One day, we were sailing in clear seas in front of the glacier. The next day, we were surrounded by icebergs the size of aircraft carriers.

As we later learned from satellite images, in a matter of 48 hours or so, a mélange of ice about 21 miles wide and 15 miles deep had cracked up and scattered into the sea. It was a spooky moment. Thwaites Glacier is the size of Florida. It is the cork in the bottle of the entire West Antarctic ice sheet, which contains enough ice to raise sea levels by 10 feet. The mélange that disintegrated was not part of the glacier itself, but a mix of icebergs and sea ice that had cozied up next to it. Still, the idea that it could just fall apart overnight was mind-blowing.

“Nathaniel B. Palmer surrounded overnight by icebergs”

As it turns out, the ice breakup I witnessed was not a freak event. A few weeks ago, scientists participating in the International Thwaites Glacier Collaboration, a $25 million five-year-long joint research program between the National Science Foundation in the U.S. and the Natural Environment Research Council in the U.K., presented their latest research. They described the discovery of cracks and fissures in the Thwaites eastern ice shelf, predicting that the ice shelf could fracture like a shattered car window in as little as five years.

“It won’t scatter out into sea as quickly as what you saw when you were down there,” Erin Pettit, a glaciologist at Oregon State University and one of the lead principal investigators in the ITGC, later told me. “But the basic process is the same. The ice shelf is breaking up and could be gone in less than a decade.” Given the ongoing war for American democracy and the deadly toll of the Covid pandemic, the loss of an ice shelf on a far-away continent populated by penguins might not seem to be big news. But in fact, the West Antarctic ice sheet is one of the most important tipping points in the Earth’s climate system.

If Thwaites Glacier collapses, it opens the door for the rest of the West Antarctic ice sheet to slide into the sea. Globally, 250 million people live within three feet of high tide lines. Ten feet of sea level rise would be a world-bending catastrophe. It’s not only goodbye Miami, but goodbye to virtually every low-lying coastal city in the world. But predicting the breakup of ice sheets and the implications for future sea level rise is fraught with uncertainty. Depending on various emissions scenarios in the latest Intergovernmental Panel on Climate Change report, we could have as little as one foot of sea level rise by the end of the century, or nearly six feet of sea level rise (of course, rising seas won’t stop in 2100, but that date has become a common benchmark).

“The difference between those [models] is a lot of lives and money,” says Richard Alley, a glaciologist at Penn State University and one of the great ice scientists of our time. Alley adds: “The most likely place to generate [the worst scenario] is Thwaites.” Or to put it more urgently: “If there is going to be a climate catastrophe,” Ohio State glaciologist Ian Howat once told me, “it’s probably going to start at Thwaites.” The problem is, understanding what’s going on at Thwaites is fiendishly complex. As I wrote in 2017: “The trouble with Thwaites, which is one of the largest glaciers on the planet, is that it’s also what scientists call “a threshold system.” That means instead of melting slowly like an ice cube on a summer day, it is more like a house of cards: It’s stable until it is pushed too far, then it collapses.”

Thwaites is very different from other big glaciers, such as those in Greenland. For one thing, it is not melting from above, due to warmer air temperatures. It’s melting from below, due to warmer ocean water eating away at its underbelly. More importantly, the terrain beneath the West Antarctic ice sheet is peculiar. “Think of it as a giant soup bowl filled with ice,” Sridhar Anandakrishnan, an expert in polar glaciology at Penn State University, once told me. In the bowl analogy, the edge of the glacier — the spot where a glacier leaves the land and begins to float — is perched on the lip of the bowl 1,000 feet or more below sea level. Scientists call that lip the “grounding line.” Below the lip, the terrain falls away on a downward slope for hundreds of miles, all the way to the Transantarctic Mountains that divide East and West Antarctica. At the deepest part of the basin, the ice is about two miles thick.

What this means is that once the warm water gets below ice, it can flow down the slope of the bowl, weakening the ice from below. Through a mechanism called “marine ice-cliff Instability,” you can get what amounts to a runaway collapse of the ice sheet that could raise global sea levels very high, very fast. That’s why, when I wrote my 2017 Rolling Stone story about Thwaites, I dubbed it “The Doomsday Glacier.” (The name stuck — if you type the phrase into Google now, you get half a million hits.) In a worst-case scenario, how fast could Thwaites collapse? No one knows. The IPCC data is the best guide for sea level rise for the rest of this century, although Alley cautions me that even six feet of sea level rise by 2100 is not the worst-case scenario.

“We just don’t know what the upper boundary is for how fast this can happen,” Alley says. “We are dealing with an event that no human has ever witnessed before. We have no analog for this.” In the past few years, scientists have made a lot of progress in understanding the dynamics of Thwaites. On our 2019 cruise, scientists discovered troughs in the seabed that allowed warm water to flow underneath the ice shelf. Scientists have mapped the underside of the glacier itself, tracked crevasses in the ice shelf, and located pinning points that might slow the retreat of the ice.

The change has been dramatic: “The net rate of ice loss from Thwaites Glacier is more than six times what it was in the early 1990s,” says Rob Larter, a geophysicist with the British Antarctic Survey who was the chief scientist on my trip to Antarctica in 2019. The recent news about Thwaites’ eastern ice shelf breaking up in the next five years was not really a surprise to anyone who has been tracking the science closely. After the sudden disintegration of the Larsen B ice shelf in 2002, scientists realized that Antarctica was far less stable than many had believed. The discovery of cracks and fissures at Thwaites further underscore just how dynamic the changes already underway are.

To be clear, there is a big difference between an ice shelf and the glacier itself. The ice shelf is like a thumbnail that grows out from the glacier and floats on the ocean. Because it is already floating, when it melts it doesn’t in itself contribute to sea level rise (just as when ice cubes melt in your glass, they don’t raise the level of liquid). But ice shelves are important because they buttress glaciers. Like the flying buttresses of Notre Dame, they give the walls of ice stability. And when they break up, the land-based glacier is free to flow much faster into the sea. And that does raise sea levels.

So yeah, if Thwaites loses a significant part of its ice shelf in five years, that’s a big deal. But even if a big part of the ice shelf does crack up, there is a lot of unknown complexity in how it will play out. “A first question is, if the ice-shelf breakage continues, will the whole ice shelf be lost, or will a short ice shelf remain, at least in some places?” Richard Alley emailed me. “Almost all ice-shelf ice is buttressing, generating friction that holds back the non-floating ice, so loss of part, most or all of the ice shelf will increase flow of non-floating ice into the ocean. But the most-important buttressing tends to arise closest to the grounding zone, so if a short ice shelf does remain, it may still provide important buttressing, and the speedup of flow and thinning will be smaller than they could be with full ice-shelf loss.” Here you see the problem.

Even predicting how the crackup of the ice shelf will impact the flow of the glacier is difficult to estimate. And this is only one of the uncertainties that scientists face when trying to predict whether or not Miami will be underwater by 2100. There is further uncertainty in exactly where and when the ice will fracture, how much warm water will be pushed up beneath the glacier by changing winds and ocean currents, how the character of the bed the glacier rests on will speed up or slow down the glacier’s slide into the sea. Whether the bed is hard rock or muddy till can have a big impact on the velocity of the glacier, just as the texture of snow affects how fast you ski down a mountain. “Ice is alive,” says Pettit. “It moves and flows and breaks in ways that are difficult to anticipate.”

Paradoxically, the more scientists learn about what’s going on at Thwaites, the more divergent the latest climate models have become about its future. Consider the results of two models by highly respected scientists published side by side in Nature earlier this year. One model suggests that Thwaites stays fairly stable until temperatures rise above 2 C of warming. Then all hell breaks loose. Thwaites begins to fall into the sea like a line of dominoes pushed off a table and soon takes the rest of the West Antarctic ice sheet with it.

And once the collapse begins, according to this model, it will be impossible to stop — at least on any human time scale. In a century or so, global sea levels could rise 10 feet, which would swamp South Florida and Bangladesh and many other low-lying regions of the world. In the other model, global sea level rise only differs by 4½ inches between a 1.5 C global temperature rise and a 3 C temperature rise (which is a little above where we are headed with under current emissions scenarios). And much of that comes from increased melt in Greenland and mountain glaciers. As for Antarctica, the paper says explicitly: “No clear dependence on emissions scenario emerges for Antarctica.”

So what to make of all this? “The current divergence among model predictions is actually a good sign because it means that scientists are probing different parameterizations, representations of processes, and hypotheses,” writes Jeremy Bassis, a geophysicist at the University of Michigan. Bassis suggests not focusing so much on the long-term uncertainty and highlighting instead what scientists know about the next few decades. “The skill of models in predicting sea level change on decadal time scales is high, and we already have actionable projections on these time scales. We should be emphasizing that fact in discussions with community members, stakeholders, and decision-makers, so they can move ahead with important adaptation and mitigation planning.”

“View from the deck on an expedition to Antarctica, 2013”

But in the long run, it is not clear that the dynamics of ice sheet collapse that are underway at Thwaites can be stopped. As glaciologist Eric Rignot put it in 2015, in Antarctica, “the fuse has been blown.” Even if we cut carbon emissions to zero tomorrow, warm water will continue to flow beneath the ice sheet for decades, destabilizing the ice and further pushing the glacier toward eventual collapse. This doesn’t means that cutting carbon pollution to zero isn’t an important goal — nothing, in fact, is more important or more urgent. “We may have a small safety margin in Antarctica, but not a large one,” says Alley. Even if the fuse is blown, cutting emissions fast could slow it all down to a millennium-long crack-up that will give us more time to adapt. One way or another, our future is written in ice.

Is This What a Climate Catastrophe Looks Like in Real Time?
by   /  March 20, 2019

“Yesterday, the Nathaniel B. Palmer left Antarctica behind and made the turn toward home. The last science experiments were completed, and the ship headed north, toward Punta Arenas, Chile, where our two-month journey will end. Scientists on board are packing up equipment and writing rough drafts of papers based on discoveries they made during our adventure into uncharted waters around Thwaites glacier. But an almost existential question looms above it all: Did we just witness what amounts to a climate catastrophe playing out in real time? On March 3rd, Bastien Queste, an oceanographer at the University of East Anglia who is a key member of the science team aboard the ship, got a WhatsApp message from a colleague back in the UK. She had sent him a satellite image of Thwaites glacier and the surrounding region in West Antarctica.

At the time, we had just completed our own close encounter with the awesome craggy blue glacier and were only a few miles away, mapping the seabed in front of the glacier with the ship’s sonar device. On this trip, satellite images have been indispensable in helping scientists track the ever-changing ice in the regions we’ve been exploring. But the map Queste received that morning was different. He noticed dark cracks in parts of the ice shelf, which floats out over the sea like a huge fingernail from the glacier itself. They had not been there before. The ice shelf was clearly starting to break up. Queste’s first thought: “Oh, shit.” Queste knew as well as anyone, the whole point of this research trip is to better understand the risk of collapse of Thwaites glacier, one of the most consequential tipping points in the Earth’s climate system.

It’s not just that Thwaites is big, although it is (imagine a glacier the size of Florida). But because of how the glacier terminates in deep water, as well as the reverse slope of the ground beneath it, Thwaites is vulnerable to particularly rapid collapse. Even more troubling, Thwaites is like the cork in the wine bottle for the rest of the West Antarctica ice sheet. If Thwaites were to fall apart, scientists fear the entire ice sheet could begin to collapse, eventually raising sea levels more than 10 feet. That’s what Queste’s “oh, shit” was about. It was non-scientific-but-very-human-shorthand for, “Is Thwaites falling apart in real time, right before our eyes?” Queste showed the image to Rob Larter, the chief scientist on the Palmer. Larter was not entirely surprised by what he saw.

A few days earlier, as we cruised along the front of Thwaites, Larter had remarked on how chaotic and jumbled the ice shelf looked. “I thought something like this might happen because of how broken up the ice on the shelf appeared,” he says. Over the next few days, Queste and Larter — as well as nearly every other scientist and student on the ship — watched the disintegration of the Thwaites ice shelf. It was a spooky sensation, looking at the satellite images then looking out the window as a parade of icebergs floated right by us on their way out to sea. In a matter of 48 hours or so, a mélange of ice about 25 miles wide and 15 miles deep cracked up and scattered into the sea. As Queste says, “A part of the glacier that is as big as the city I live in — it was just gone.” Here are satellite images of Thwaites before and after the blowout. The red dot shows where the ship was located on those days.

For scientists both on and off the ship, the big question is, was the blowout a sign that Thwaites is collapsing before our eyes, or was it a more or less ordinary event in the lifecycle of a big glacier? These are not easy questions to answer. Glaciers are practically alive, in flux all the time, exquisitely sensitive to small changes in atmospheric and ocean temperatures. Sometimes changes that look dramatic to non-scientists, like the breakup of the Larsen B ice shelf in Antarctica a few years ago, have an inconsequential impact on sea level rise (unlike the Thwaites ice shelf, the Larsen B is not holding back a massive city-drowning glacier).

And it’s important to point out that the Thwaites blowout is not the same thing as what scientists typically call a “calving event,” which you often see in movies and documentaries, where big slabs of ice fall off glaciers into the sea. What we witnessed was the sudden disintegration of an ice shelf, which is a very different thing. Unlike the calving of land-based ice into the sea, the break-up of an ice shelf does not itself contribute to sea level rise, because the ice is already floating — just as when the ice in your whiskey melts, the level of whiskey in your drink doesn’t rise.

“sea floor on multibeam echosounder aboard Palmer in Antarctica”

Nevertheless, ice shelves are important. They buttress the glacier itself, providing stability and in effect holding it back from slipping faster into the sea. The ice shelf that blew out at Thwaites was particularly messy and chaotic — it’s a bunch of bergs glued together with seasonal sea ice rather than a solid shelf. So maybe it wasn’t doing much to stabilize Thwaites, and the blowout wasn’t a big deal. But given the larger fragility of Thwaites, and the consequences of a sudden collapse, any dramatic change in the structure of the glacier is hardly an encouraging sign. When it comes to melting glaciers and sea level rise, climate scientists have traditionally been far more concerned about Greenland than Antarctica.

In our warming world, Antarctica was viewed as a stable place: very big, very cold, very distant. Then, in the early 1990s, improved satellite observations proved those assumptions were wrong. Of special concern was West Antarctica, which is particularly vulnerable to warm Circumpolar Deep Water attacking the glaciers from below. A recent paper co-authored by scientists from NASA’s Jet Propulsion Laboratory in California noted that the main trunk of Thwaites accelerated 33 percent between 2006 and 2013 — it’s now sliding into the sea at a rate of about two miles per year. In addition, parts of the glacier are thinning by as much as 13 feet each year. Here’s a GIF that captures how much Thwaites has changed in just the past five years. The orange and red sections are the fastest flowing parts of the glacier.

And here’s a graph that shows how quickly the ice flow on Thwaites has accelerated — it’s almost doubled in the last five years. So what does all this mean? Nobody can say for sure. “I’m holding my breath to see what happens next,” says Larter. “The blowout could be the start of a new phase of the evolution of Thwaites glacier. But I’m wary, because sometimes you see things that you think are going to be the start of something big, and then things settle down. I think it’s too early to say which way this is going to go.”

In an email, Eric Rignot, a senior scientist at NASA’s Jet Propulsion Laboratory who has co-authored recent papers suggesting the collapse of Thwaites is already past the point of no return, told me that he wouldn’t view the blowout as particularly alarming unless he saw retreat of the front of the glacier itself during the process (which, in the most recent satellite images, he hasn’t). But Rignot ended his email to me with an important note: “This sort of event is a good reminder that changes can happen fast in these environments, even though it may seem that nothing much is happening when you are staring at the glacier from a ship deck, right?”

Richard Alley, a highly respected glaciologist at Penn State, had a more nuanced view of it all. Alley (who, like Rignot, is not on the ship) pointed out that because the ice shelf that blew out was already pretty chaotic, it was likely not providing much stability to the glacier. “So its loss is not a huge issue for the still-grounded ice,” Alley emailed. “But the chaotic ice was still doing something.” He compared Thwaites to glaciers in Greenland, where the blowout of similar mélanges are often followed by calving of ice from the glacier itself, which is far more troubling. Alley also pointed out that the loss of ice shelves leaves glaciers vulnerable to stress from what he called “remote forcing” — storms across the Pacific, or tsunamis from an earthquake.

“To stretch the analogy a little bit,” Alley said, “if Thwaites were a car, you could say that it has lost part of its bumper. And, while that’s not hugely important, it is part of a pattern that is pointing toward larger changes to come.” This is, in short, what makes climate change so alarming, and so unlike other threats that humans have faced. By loading the atmosphere with carbon, we are messing with a system that even the best scientists in the world don’t fully understand. Individual events are hard to interpret in real time. “In the history of human civilization, we’ve never seen the rapid collapse of a glacier like Thwaites,” Larter points out.

“So we don’t know how exactly it starts, or what it looks like while it’s happening.” But in the long run, the arc of uncertainty bends toward catastrophe. It may be that this blowout at Thwaites was driven by wind or a shift in ocean temperature that, in the big picture, means little. Or it may be further evidence that the collapse of Thwaites is already underway, and it’s only a matter of time — perhaps even during the lifetimes of kids alive today — before virtually every coastal city from Miami to Jakarta is under six, seven, eight or more feet of water. If that’s the case, then big parts of the world we live in today may already be doomed. We just don’t know yet.”





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