The beginning of the disaster? Antarctica is melting at an alarming and unexpected rate

The beginning of the disaster? Antarctica is melting at an alarming and unexpected rate

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Deep in the South Pole, there is a nightmarish ice melt scenario - and a rapid rise in the waters - that could usher in disaster.

The Thwaites Glacier, in West Antarctica, is so remote that only 28 humans have ever set foot on it. Knut Christianson, a 33-year-old glaciologist at the University of Washington, has been twice. A couple of years ago, Christianson and a team of seven scientists traveled more than 1,600 kilometers from McMurdo Base, the largest research base in Antarctica, to spend six weeks at the Thwaites.

What they were mapping was a future global disaster. As the world warms, determining exactly how quickly ice is melting and seas are rising may be one of the biggest questions of our age. Half of the world's population lives 80 kilometers from some coast. There are trillions of dollars of property located on the beaches and crowded together in low-lying cities like Miami and New York. A long, slow rise in the waters over the next few decades can be manageable. But a more abrupt one, no. "If there's going to be a climate catastrophe," says Ohio State glaciologist Ian Howat, "it's probably going to start in Thwaites."

The problem with the Thwaites, one of the largest glaciers on the planet, is that it is also what scientists call "a threshold system." This means that instead of slowly melting like an ice cube on a summer day, it is more like a house of cards: it is stable until overstretched, and then collapses.

But in recent years, things have gotten weird in Antarctica. The first alarming event was the sudden collapse, in 2002, of the Larsen B ice shelf, a huge chunk of ice off the Antarctic Peninsula. An ice shelf is like a giant fingernail that grows at the end of a glacier when it hits water. The glaciers behind Larsen B, like many others in both Antarctica and Greenland, are known as "marine termination" glaciers because large portions of them are below sea level. The collapse of the ice shelves does not, in itself, contribute to the rise in the water level, since they are already floating (just as ice that melts in a glass does not raise the level of the liquid). But they play an important role in strengthening, or restraining, glaciers. After the Larsen B ice shelf collapsed, the glaciers behind it began to fall into the water at a speed eight times faster than before. "It was like, 'Oh, what's going on here?'" Says Ted Scambos, the chief scientist at the National Snow and Ice Data Center in Boulder, Colorado. "It turns out that glaciers are much more sensitive than anyone had thought."

Soon - possibly even by the time you're reading this - a piece of the Larsen C ice shelf is going to break apart and float into the ocean surrounding Antarctica. The breakdown of the Larsen C, a close cousin of the Larsen B, which occurred in 2002, has been developing for several years. But in recent months, it has escalated dramatically. As I write this, the crack is already over 100 miles long. Such a collapse of the ice shelves is exactly what Mercer predicted would be the first sign that disaster was imminent. When it does break, it will likely be a newspaper cover, cited as proof that Antarctica is rapidly crumbling.

But it also may not. "Ice barriers break all the time, and sometimes it's not a problem," says Alley, who was a student at Ohio University when Mercer was a senior professor there. "It will depend a lot on what we see after the barriers are broken, and how the glaciers in the area react." Alley points out that the glaciers behind the Larsen C barrier are modest, and even if they all accelerate and fall into the water, it probably only makes a centimeter difference in the rise in water level. In other words, this cleft itself is not what Alley calls "a hysterical cry for the end of the world." But it also doesn't mean that such a disaster is not in progress in West Antarctica, just on a slightly slower timescale.

In recent decades, new satellite technologies have given scientists a clearer picture of what is happening in West Antarctica, and much of it confirmed Mercer's hypothesis. From space, it is possible to measure changes in the width of the ice, as well as the speed with which glaciers such as Thwaites retract, and move away from the support line. And the news is not good. In 2014, two highly respected ice scientists, Eric Rignot of NASA and Ian Joughin of the University of Washington, published separate articles reaching the same conclusion. As Joughin put it: "Our simulations provide clear evidence that the destabilization process of sea ice sheets is already advancing on the Thwaites Glacier." In an interview, Rignot was more succinct. In West Antarctica, he said, "we already blew the fuse."

At more than 90 meters high, the ice cliffs in front of the Jakobshavn are the highest on the planet. There is a good reason for it. Alley and other scientists found that ice cliffs in marine termination glaciers such as Jakobshavn or Thwaites have a structural limit of around 90 meters; after all, they collapse from the weight. So while there are sections of the Thwaites that are 1,800 meters deep, Alley realized, the structural integrity of the ice wouldn't allow the glacier front to stand that high. In other words, glaciers with a frontage of up to 90 meters can be relatively stable; after that, forget it. As Alley tells me: "They just collapse, collapse, collapse."

One of the ways that scientists test how well a model can predict the future is to see how well it recreates the past. If you can test a model backwards and get the correct results, you can test it forward and trust that the results will be adequate. For years, DeConto and Pollard were trying to get their model to recreate the Pliocene, the era three million years ago when CO2 levels in the atmosphere were close to what they are now, except that the waters were six meters higher. . But no matter what buttons they hit, they couldn't get their model to melt the ice shelves fast enough to replicate what the geological archive told them had happened. "We knew something was missing in the dynamics of our model," DeConto tells me.

Alley suggested they bring in their new understanding of ice physics, including the structural integrity of the ice itself (or its absence), and "see what happens." They did and oh, the model worked. They were able to make the Pliocene melt as it should. In effect, they found the missing mechanism. His model was now tested.

Of course, the next thing DeConto and Pollard did was test it forward. What they found is that, in high-emission scenarios - that is, the path we are on today - rather than a contribution to near-zero sea level rise from Antarctica by 2100, there was over a meter, mostly from West Antarctica. If you add a fairly conservative estimate of Greenland's contribution to sea level rise in the same time, as well as the expansion of the oceans, you have more than a meter and a half. That is, twice the highest IPCC scenario.

In any case, the threat is clear. In a rational world, awareness of these risks would lead to rapid and deep cuts in carbon pollution to slow warming, as well as investments in more research in West Antarctica, to better understand what is happening. Instead, the Americans elected a president who thinks climate change is a sham, who is hell-bent on burning more fossil fuels, who installs the CEO of the world's largest oil company as secretary of state, who wants to cut the climate science budget and instead spend nearly $ 70 billion to build a wall on the Mexican border and another $ 54 billion to bolster the military.

In the end, no one can know exactly how long the glaciers of West Antarctica are going to be stable. "We don't know what the upper limit is for how fast this can happen," says Alley, and he sounds a little scared. “We are dealing with an event that no human has ever witnessed. We don't have an analogy for this. " But it's clear that thanks to our 200-year binge on fossil fuels, the collapse of West Antarctica is on its way, and that all Miami Beach condo owners, and farmers in Bangladesh, are living at the mercy of the physics of the world. ice. Alley himself never said so, but in West Antarctica, scientists discovered the engine of the catastrophe.

Jeff Goodell

Read the full Article

Video: Antarctic ice sheet is melting at fastest rate ever (June 2022).


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