One thing that is difficult to understand about the climate crisis is that major changes can happen quickly. In 2019, I was on board Nathaniel B. Palmer, a 308-foot-long scientific research vessel cruising in front of the Thwaites Glacier in Antarctica. One day we sailed in clear sea 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, a mixture of ice about 21 miles wide and 15 miles deep in 48 hours was torn up and scattered into the ocean.
It was an eerie moment. The Thwaites Glacier is the size of Florida. It is the stopper of the bottle on the entire West Antarctic ice sheet, which contains enough ice to raise sea levels by 10 feet. The mixture that went into solution was not part of the glacier itself, but a mixture of icebergs and sea ice that had enjoyed themselves next to it. Still, the thought that it could just fall apart overnight was amazing.
As it turns out, the icebreaker I witnessed was not a freak event. A few weeks ago, researchers participating in the International Thwaites Glacier Collaboration, a five-year joint $ 25 million research program between the National Science Foundation in the United States and the Natural Environment Research Council in the United Kingdom, presented their latest research. They described the discovery of cracks and fissures in Thwaite’s eastern ice shelf and predicted that the ice shelf could crack like a broken car window in as little as five years. “It will not spread into the ocean as fast as what you saw when you were down there,” Erin Pettit, a glaciologist at Oregon State University and one of the leading chief investigators at the ITGC, later told me. “But the basic process is the same. The ice shelf is about to break up and may be gone in less than a decade.”
Given the ongoing war for American democracy and the deadly number of the Covid pandemic, the loss of an ice shelf on a remote continent populated by penguins may not seem like big news. But in fact, the West Antarctic ice sheet is one of the most important turning points in the Earth’s climate system. If the Thwaites Glacier collapses, it will open the door for the rest of the West Antarctic ice sheet to slide into the ocean. Globally, 250 million people live within three feet of high tide. A ten-foot rise in sea level would be a worldwide disaster. It’s not only goodbye to Miami, but goodbye to pretty much every low-lying coastal city in the world.
But predicting the collapse of the ice sheets and the consequences for future sea level rise is fraught with uncertainty. Depending on different emission scenarios in the latest report from the Intergovernmental Panel on Climate Change, we could have as little as a foot sea level rise by the end of the century, or almost six feet sea level rise (of course rising sea did not stop in 2100, but that date is become a common benchmark). “The difference between them [models] is a lot of life 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 to be a climate catastrophe,” Ohio State glaciologist Ian Howat once told me, “it will probably start at Thwaites.”
The problem is that it’s devilishly complex to understand what’s going on with Thwaites. As I wrote in 2017:
The problem with Thwaites, which is one of the largest glaciers on the planet, is that it is also what scientists call “a threshold system.” This means that instead of melting slowly like an ice cube on a summer day, it’s more like a house of cards: it’s stable until it’s pushed too far, then it collapses.
Thwaites are very different from other large glaciers, such as those in Greenland. First, it does not melt from above due to warmer air temperatures. It melts from below due to warmer seawater that eats at its abdomen. 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 place where a glacier leaves the land and begins to flow – is located on the edge 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 downhill slope for hundreds of miles, all the way to the transantarctic mountains that divide the East and West Antarctic. At the deepest part of the basin, the ice is about two miles thick.
What this means is that when the hot water comes under ice, it can flow down the slope of the bowl, weakening the ice from below. Through a mechanism called “marine iceberg instability”, you can get what is equivalent to a runaway collapse of the ice cap that can raise global sea levels very high, very fast.
That’s why I wrote my 2017 Rolling stones the story of Thwaites, I christened it “Doomsday Glacier”. (The name is stuck – if you type the phrase in Google now, you will get half a million hits.)
At worst, how quickly could Thwaite collapse? No one knows. The IPCC data is the best guide to sea level rise for the rest of this century, though Alley warns me that even six feet of sea level rise in 2100 is does not the worst case scenario.
“We just do not know what the upper limit 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 analogue for this. “
In the last few years, scientists have made great strides in understanding Thwaite’s dynamics. On our cruise in 2019, scientists discovered troughs in the ocean floor that allowed hot water to flow under the ice shelf. Researchers have mapped the underside of the glacier itself, traced cracks in the ice shelf and located attachment points that could slow the ice retreat. 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,” said Rob Larter, a British Antarctic Survey geophysicist who conducted research on my trip. to Antarctica in 2019.
The latest news about Thwaites’ eastern ice shelf disintegrating over the next five years was not really a surprise to anyone who has been following science closely. After the sudden dissolution of the Larsen B ice shelf in 2002, researchers realized that Antarctica was far less stable than many had thought. The discovery of cracks and fissures at Thwaites further underscores how dynamic the already ongoing changes 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 of the glacier and floats on the ocean. Because it is already floating, it does not in itself contribute to sea level rise when it melts (just like when ice cubes melt in your glass, they do not raise the liquid level).
But ice shelves are important because they support glaciers. Like Notre Dame’s flying pillars, they provide ice wall stability. And when they break up, the land-based glacier is free to float much faster into the ocean. And it do raise sea levels.
So yes, if Thwaites loses a significant portion of its ice shelf in five years, that’s a big deal.
But even though much of the ice shelf is cracking, there is a lot of unknown complexity in how it will unfold. “A first question is, if the ice shelf break continues, will the entire ice shelf be lost, or will a short ice shelf remain, at least in some places?” Richard Alley sent me an email. “Almost all ice shelf ice encounters, generating friction that holds the non-floating ice back, so loss of part, most or all of the ice shelf will increase the flow of non-floating ice in the ocean. But the most important “Support tends to occur closest to the grounding zone, so if a short ice shelf is still left, it can still provide significant support, and the rate of flow and thinning will be less than they could be with full ice shelf loss.”
Here you see the problem. Even predicting how the crack of the ice shelf will affect the flow of the glacier is difficult to estimate.
And this is just one of the uncertainties that scientists face when trying to predict whether Miami will be underwater in 2100. There is further uncertainty about exactly where and when the ice will burst, how much hot water that will be pushed up under the glacier. by changing winds and ocean currents, how the character of the bottom on which the glacier rests will accelerate or slow down the glacier’s slippage into the ocean. Whether the bed is hard rock or muddy until can have a big impact on the speed of the glacier, just as the texture of the snow affects how fast you ski down a mountain. “The ice is alive,” Pettit says. “It moves and flows and breaks in ways that are hard to predict.”
Paradoxically, the more scientists learn about what’s going on at Thwaites, the more divergent recent climate models have become about its future. Consider the results of two models of highly respected scientists published side by side in Nature earlier this year. One model suggests that Thwaites remains fairly stable until the temperature rises above 2 C for heating. Then hell breaks loose. Thwaites begins to fall into the sea as a series of dominoes pushed from a table and soon takes with them the rest of the West Antarctic ice sheet. 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 flood southern Florida and Bangladesh and many other low-lying regions of the world.
In the second model, the global sea level rise differs by only 4½ inches between a global temperature rise of 1.5 C and a temperature rise of 3 C (which is slightly above where we are heading under the current emission scenarios). And much of it comes from increased melting in Greenland and mountain glaciers. With regard to Antarctica, the newspaper explicitly states: “There is no clear dependence on emissions for Antarctica.”
So what to do about all this?
“The current divergence between model predictions is actually a good sign because it means that researchers are studying 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 instead highlighting what scientists know about the next few decades. “The ability of models to predict sea level changes on decades’ time scales is high, and we already have action-oriented projections on these time scales. We should emphasize this fact in discussions with community members, stakeholders and decision makers so they can move forward with important adaptation and mitigation planning. . “
But in the long run, it is not clear that the dynamics of the collapse of the ice sheet that is underway at Thwaites can be stopped. As glaciologist Eric Rignot put it in 2015, in Antarctica, “the fuse has blown.” Even if we reduce carbon emissions to zero tomorrow, hot water will continue to flow under the ice sheet for decades, destabilizing the ice and further pushing the glacier toward a possible collapse. This does not mean that reducing carbon pollution to zero is not an important goal – nothing is actually more important or more urgent. “We may have a small safety margin in Antarctica, but not a large one,” Alley says. Even though the fuse is blown, a rapid cut in emissions could slow it all down to a millennium-long breakup that will give us more time to adjust. Somehow our future is written in ice.
Contributing editor Jeff Goodell has written extensively on Doomsday Glacier. You can listen to an audio story from his trip to Thwaites here.