In a remote region of Antarctica known as Pine Island Bay, 2,500 miles from the tip of South America, two glaciers retain human civilization.
These glaciers extend across an icy plain more than 150 miles long. Island and Thwaites have marched constantly for millennia to the Amundsen Sea, part of the vast Southern Ocean. Further inland, the glaciers widen in a two-mile-thick ice reserve that covers an area the size of Texas.
There is no doubt that this ice will melt as the world heats up. The vital question is when.
The Pine Island Bay glaciers are two of the largest and fastest melting glaciers in Antarctica. (A feature of Rolling Stone earlier this year dubbed Thwaites "The Doomsday Glacier"). Together, they act as a plug that holds enough ice to pour 11 feet of sea level into the world's oceans, an amount that would submerge all coastal cities. in the planet. For that reason, discovering how fast these glaciers will collapse is one of the most important scientific issues in the world today.
To find out, scientists have been looking back until the end of the last ice age, around 11,000 years. back, when global temperatures remained approximately at their current levels. The bad news? There is increasing evidence that Pine Island Bay glaciers quickly collapsed at that time, flooding the world's coasts, partly as a result of so-called "sea cliff instability".
The bottom of the ocean is accentuated towards the center of this part of Antarctica, so each new iceberg that breaks exposes higher and higher cliffs. The ice becomes so heavy that these higher cliffs do not support their own weight.
"The ice is so strong that it will collapse if these cliffs reach a certain height," explains Kristin Poinar, glacier at NASA's Goddard Space Flight. Center. "We need to know how fast it's going to happen."
In recent years, scientists have identified the instability of the sea cliffs as a feedback loop that could drive the disintegration of the West Antarctic Ice Sheet this century – much faster than previously thought.
Small ice fragments the size of a skyscraper collapsed in the sea, as tall as the Statue of Liberty and as deep under the water as the height of the Empire State Building. The result: a global catastrophe never seen before.
Ice has many forms, with different consequences when it melts. Floating ice, such as that which covers the Arctic Ocean during winter and includes ice shelves, does not raise sea level. (Think of a bucket of melted ice, which will not spill a drink.)
Land ice, on the other hand, is much more problematic. When it falls into the ocean, the total volume of liquid in the seas increases. Therefore, the rise in sea level.
Antarctica is a giant landmbad, about half the size of Africa, and the ice that covers it averages more than a mile thick. Before human combustion of fossil fuels triggered global warming, the ice of the continent was in relative equilibrium: the snows of the interior of the continent equaled the icebergs that were detached from the glaciers at their edges.
Now, carbon dioxide traps more heat in the atmosphere and warms the planet, the scales have tipped.
A wholesale collapse of Pine Island and Thwaites would trigger a catastrophe. The giant icebergs would flow away from Antarctica like a parade of frozen soldiers. Around the world, high tides would rise higher, slowly burying each coastal line of the planet, flooding coastal cities and creating hundreds of millions of climate refugees.
All this could work in only 20 or 50 years, too fast for humanity to adapt
"With the instability of the sea ice cliffs, the rise in sea level for the next century is potentially much more great than we thought it would be five or 10 years ago, "says Poinar.
Much of this newly discovered concern is driven by the research of two climatologists: Rob DeConto at the University of Mbadachusetts-Amherst and David Pollard at the Pennsylvania State University. A study they published last year was the first to incorporate the latest understanding of sea cliff instability in a continental-scale Antarctic model.
Their results yielded estimates of how high the sea level could rise this century.  "The Antarctic model raises the possibility of an indestructible collapse of ice," said the head of the scientific journal Nature, a publication that is not known for hyperbole.
Instead of a three-foot increase in ocean levels before the turn of the century, six feet was more likely, according to the findings of DeConto and Pollard. But if carbon emissions continue to track something like the worst, the 11 full feet of ice encased in West Antarctica could be released, his study showed.
Three feet of sea level rise would be bad, which would lead to the most frequent floods in the US cities. UU like New Orleans, Houston, New York and Miami. The island nations of the Pacific, such as the Marshall Islands, would lose most of their territory. Unfortunately, now it seems that three feet is possible only under the best scenarios.
However, at six feet, around 12 million people in the United States would be displaced, and the most vulnerable megacities in the world, such as Shanghai, Mumbai, and Ho Chi Minh City, could be wiped off the map.
At 11 feet, the land currently inhabited by hundreds of millions of people in the world would end up underwater.
Twice a month, Hurricane Sandys
south of Florida would be largely uninhabitable; Floods on the scale of Hurricane Sandy would hit twice a month in New York and New Jersey, since the tug of the moon alone would be enough to send tides to houses and buildings.
The advance of DeConto and Pollard came from trying to match the observations of ancient sea levels on coasts around the world with the current behavior of the ice sheet.
About 3 million years ago, when global temperatures were as warm as expected at the end of this century, the oceans were dozens of feet higher than today.
Previous models suggested that it would take hundreds or thousands of years for an increase in sea level of that magnitude to occur. But once they explained the instability of the sea cliffs, the DeConto and Pollard model pointed to a catastrophe if the world maintains a "normal" path, which means that we do not drastically reduce carbon emissions.
Rapid cuts in greenhouse gases however, showed that Antarctica remained almost completely intact for hundreds of years.
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Pollard and DeConto are the first to admit that their model is still crude, but their results have pushed the entire scientific community to the mode of emergency.
The entire scientific community is in emergency mode
"It could happen faster or slower, I do not think we really know it yet," says Jeremy Bbadis, a leading ice layer scientist at the University of Michigan . "But it is within the scope of possibility, and that is something that is scary."
Scientists used to think that ice sheets could take millennia to respond to changing climates. These are, after all, chunks of ice a mile thick.
The new evidence, however, says that once a certain temperature threshold is reached, the ice shelves of the glaciers that extend to the sea, such as those near Pine Island Bay, begin to melt both from above and from below, weakening its structure and accelerating its disappearance, and paving the way for the instability of the cliff to arrive.
In a new study published last month in the journal Nature, a team of scientists from Cambridge and Sweden point to evidence of the thousands of scratches left by ancient icebergs on the ocean floor, indicating that glaciers of Pine Island broke up in a relatively short time at the end of the last ice age.
The only place in the world where you can see the instability of the ice cliff in action today is on the Jakobshavn Glacier in Greenland, one of the fastest collapsing glaciers in the world. DeConto says that to build their model, they took Jakobshavn's collapse rate, cut it in half to be more conservative, then applied it to Thwaites and Pine Island.
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But there are reasons to think that Thwaites and Pine Island could go even faster than Jakobshavn.
At this time, there is a floating ice shelf that protects the two glaciers, helping to contain the flow of ice in the ocean. But recent examples from other regions, such as the Larsen B ice shelf, which is rapidly collapsing on the Antarctic Peninsula, show that once the ice shelves are broken as a result of warming, their parent glaciers begin to flow faster towards the sea, an effect that can weaken the stability of the ice inland, too.
"If you remove the ice shelf, there is the potential that not only ice cliff instabilities begin, but a process called instabilities of the sea ice layer," says Matthew Wise, a polar scientist at the University of California. Cambridge
This points to the possible rapid destabilization of the entire ice sheet of West Antarctica in this century.
"Once the tensions overcome the resistance of the ice," says Wise, "it just falls off." . "
And, it's not just Pine Island Bay, in our current course, other glaciers around Antarctica will be equally vulnerable, and then there's Greenland, which could contribute up to 20 feet of sea level rise if it melts. 19659048] Next to a meteorite, the rapid rise in sea level due to the collapse of the cliffs is one of the fastest ways to remake our world itself.
This is as fast as climate change becomes
] Still, some scientists are not entirely convinced that the alarm is justified, Ted Scambos, a leading scientist at the National Snow and Ice Data Center in Colorado, says the new research by Wise and his colleagues, which identified the The instability of the ice cliff on Pine Island Bay 11,000 years ago is "tempting evidence." But he says research does not establish how quickly it happened.
"There is much more to be understood if we are going to use this mechanism to predict how much the Thwaites Glacier and the other glaciers will retreat. " he says. "The question comes down to, what are the brakes in this process?"
Scambos thinks it is unlikely that Thwaites or Pine Island would collapse at once. On the one hand, if a rapid collapse were to occur, it would produce a pile of icebergs that could act as a temporary ice, slowing down the recoil rate.
Despite differences of opinion, however, there is growing agreement within the community that we need to do much more to determine the risk of a rapid rise in sea level. In 2015, the US governments UU And the United Kingdom began to plan a joint program of rare and urgent research to study the Thwaites glacier. Called "How much, how fast?", The effort will begin next year and will last five years.
Seeing the two governments grouping their resources is "really a sign of the importance of an investigation like this," NASA's Poinar says.
Considering what is at stake, the research program in Thwaites is not enough, but it could be what the researchers can obtain the most. "Realistically, everything that can be done in the next five years is likely to be in the current funding environment," says Pollard.
It refers, of course, to the Trump administration's contempt for science and adequate scientific funding; The White House budget proposal for 2018 includes the first cut to the National Science Foundation, which typically finances research in Antarctica.
"It would be sensible to make a big effort in this, from my perspective," says Pollard. Structural engineers need to study the key glaciers of Antarctica as if they were badyzing a building, he says, looking for the weak points and understanding how they might fail. "If you increase the research a lot now, [the cost] would still be trivial compared to the losses that could occur."
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