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At the bottom of the world, the floating edges of one of the enormous ice sheets covering Antarctica face an invisible threat, which could contribute to rising sea levels around the world. They are melting from below.
As the planet warms, greater volumes of warm water are washing over the underside of the West Antarctic ice shelves, the giant tongues of ice at the tips of glaciers. The large mass of these platforms prevents land ice from flowing more quickly into the open sea. So, as the shelves melt and thin, more land ice moves into the ocean, eventually contributing to sea level rise. Curbing fossil fuel emissions could help slow this melting, but scientists aren’t sure to what extent.
Now, researchers in Great Britain We’ve crunched the numbers and come to a sobering conclusion: a certain amount of accelerated melting is essentially locked in. Even if nations limited global warming to 1.5 degrees Celsius, or 2.7 Fahrenheit, it wouldn’t do much to stop weight loss. Staying below 1.5 degrees Celsius is the most ambitious goal of the Paris Agreement and, for the moment, it is unlikely to be achieved.
“We appear to have lost control of the melting of the West Antarctic ice shelf over the course of the 21st century,” one of the researchers, Kaitlin A. Naughten, an ocean scientist at the British Antarctic Survey, said at a news conference. “That most likely means some sea level rise that we can’t avoid.”
The findings of Dr. Naughten and her colleagues, which were published on monday in the journal Nature Climate Change, add to a litany of gloomy forecasts for ice on the western side of the frozen continent.
Two of the region’s fastest-moving glaciers, Thwaites and Pine Island, have been losing large amounts of ice to the ocean for decades. Scientists are trying to determine when greenhouse gas emissions could push the West Antarctic ice sheet past a “tipping point” beyond which its collapse becomes rapid and difficult to reverse, endangering coasts around the world in the coming centuries.
Still, reducing emissions of heat-trapping gases could still prevent even larger amounts of Antarctic ice from spilling into the seas. The East Antarctic Ice Sheet contains about 10 times more ice than that of West Antarctica, and previous studies suggest it is less vulnerable to global warming, even if some recent research has challenged that opinion.
“We can still save the rest of the Antarctic ice sheet,” said Alberto Naveira Garabato, an oceanographer at the University of Southampton who was not involved in the new research, “if we learn from our past inaction and start reducing gas emissions.” greenhouse effect”. now.”
Dr. Naughten and her colleagues focused on the interaction between ice shelves and the water of the Amundsen Sea, which is the part of the Southern Ocean that bathes the Thwaites and Pine Island glaciers.
Researchers for the first time used computer simulations to estimate changes in ocean temperature and the subsequent melting of the ice shelf that took place there in the 20th century. They then compared this to potential changes under various pathways for global warming in the 21st century, from very optimistic to unrealistically pessimistic.
They found that water 200 to 700 meters, or 650 to 2,300 feet, below the surface of the Amundsen Sea could warm more than threefold in the coming decades compared to the last century, virtually regardless of what happen with emissions.
If global warming were limited to 1.5 degrees Celsius compared to pre-industrial conditions, temperatures in Amundsen would stabilize somewhat after about 2060. Under the most dire emissions trajectory, by contrast, ocean warming would accelerate even further after 2045.
The reason the differences are not greater is that water temperatures in this part of the Southern Ocean are influenced not only by human-driven warming of the atmosphere, but also by natural climate cycles such as El Niño, said Dr .Naughten. The differences between the various emissions trajectories, he said, are small by comparison.
The study is unlikely to be the final word on the fate of the West Antarctic ice shelves. Scientists didn’t start collecting data on melting there until 1994, and because of the difficulty of making measurements under such extreme conditions, data is still sparse.
“We rely almost exclusively on models here,” Dr. Naughten said.
When mathematical representations of reality are the best option available, scientists prefer to test their hypotheses using several to ensure that their findings are not the product of the peculiarities of a given model. Dr. Naughten and her colleagues used a single model of ice-ocean interactions.
Still, the methods of their study are largely in line with previous findings, said Tiago Segabinazzi Dotto, a scientist at Britain’s National Oceanography Center who was not involved in the new research.
This gives coastal societies reason to take the study’s predictions seriously and plan for even higher sea levels, he said.