Melting of the West Antarctic ice is inevitable – 10/25/2023 – Environment

Deep in the world, the floating edges of one of the massive ice sheets covering Antarctica are facing an invisible threat that could contribute to rising sea levels around the world. They are melting underneath.

As the planet warms, greater volumes of warm water are bathing the undersides of the West Antarctic Ice Shelves, the large tongues of ice at the edges of glaciers. The immense mass of these platforms prevents land ice from flowing more quickly into the open sea.

Therefore, as shelves melt and thin, more land ice moves toward the ocean, eventually contributing to sea level rise. Reducing fossil fuel emissions could help slow this meltdown, but scientists weren’t sure by how much.

Now, researchers in the UK have done the math and come to a worrying conclusion: a certain amount of accelerated melting is essentially guaranteed. Even if nations limit global warming to 1.5°C it wouldn’t do much to stop thinning. Remaining below 1.5°C is the most ambitious goal of the Paris Agreement and is currently unlikely to be achieved.

“It appears we may have lost control of the melting of the West Antarctic Ice Shelf over the course of the 21st century,” said one of the researchers, Kaitlin A. Naughten, an ocean scientist at the British Antarctic Survey, at a news conference. “This most likely means some level of sea level rise that we cannot avoid.”

Naughten and his colleagues’ findings, which were published Monday in the journal Nature Climate Change, add to a series of grim predictions 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 vast amounts of ice to the ocean for decades. Scientists are trying to determine when greenhouse gas emissions could push the West Antarctic Ice Sheet to a “tipping point” after which its collapse becomes rapid and difficult to reverse, endangering coastal strips around the world. around the world in the coming centuries.

Even so, reducing emissions of heat-trapping gases could still prevent even larger amounts of Antarctic ice from being lost to the seas. The East Antarctic Ice Sheet contains about ten times more ice than West Antarctica, and previous studies suggest it is less vulnerable to global warming, even though some recent research has challenged that view.

“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 greenhouse gas emissions.” now”.

Naughten and his colleagues focused on the interaction between ice shelves and water in the Amundsen Sea, which is the part of the Southern Ocean that butts up against the Thwaites and Pine Island glaciers.
The researchers first used computer simulations to estimate changes in ocean temperature and the resulting melting of ice shelves that occurred there in the 20th century.

They then compared this with possible changes in different global warming trajectories in the 21st century, from highly optimistic to unrealistically pessimistic.

They found that water 200 to 700 meters below the surface of the Amundsen Sea could warm at a rate more than three times greater in the coming decades compared with the last century, virtually regardless of what happens to emissions.

If global warming were limited to 1.5°C compared to pre-industrial conditions, temperatures in Amundsen would stabilize somewhat after about 2060. In contrast, under the most catastrophic emissions trajectory, ocean warming would further accelerate more after 2045.

The reason the differences aren’t greater is that water temperatures in this part of the Southern Ocean are influenced not only by human-caused warming of the atmosphere, but also by natural climate cycles such as El Niño, Naughten said. The differences in the various emissions trajectories, she says, are small in comparison.

The study likely won’t be the final word on the future of West Antarctic ice shelves. Scientists only began collecting data on melting in 1994, and because of the difficulty of taking measurements in such extreme conditions, data is still scarce.

“We’re relying almost entirely on models here,” Naughten said.

When mathematical representations of reality are the best option available, scientists prefer to test their hypotheses using several of them to ensure that their findings are not the product of the peculiarities of a particular model. Naughten and his colleagues used just a single model of ice-ocean interactions.

However, the methods of their study are broadly 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.

That gives coastal societies reason to take the study’s predictions seriously and plan for even higher sea levels, he said.