Antarctica’s vast ice fields and floating sea ice surrounding the continent constitute Earth’s largest heat shields, deflecting solar radiation away from the planet, but two studies published today show how global warming is encroaching even on the solar light reflector in the coldest region on the planet.
Research by scientists from the British Antarctic Survey focused on the precipitous decline in sea ice that occurred last year. During the southern winter of 2023, sea ice extent in Antarctica was about 770,000 square miles less than average, an area larger than Alaska.
Lead author Rachel Diamond said the modeling study showed such an extreme decline would be a once-in-2,000-year event without climate change, “which tells us the event was very extreme.” , she said. “A figure less than one in 100 is considered exceptionally unlikely.”
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In a separate paper, another team of scientists documented how strong tides push seawater surprisingly far beneath the tongue of the Thwaites Glacier in West Antarctica, reinforcing concerns about accelerating glacier melt and to sea level rise.
“Pressurized seawater intrusions will cause vigorous melting of ground ice for miles, making the glacier more vulnerable to ocean warming and increasing projections of ice mass loss,” the authors write in the article published in the Proceedings of the National Academy of Sciences. .
“The problem is that we underestimate the speed at which the glacier is changing, which would be devastating for coastal communities around the world,” said co-author Christine Dow, a professor in the University’s Faculty of Environment. from Waterloo in Ontario, Canada.
In this study, scientists tracked the course of seawater by analyzing data from sensitive radar instruments that can detect when the ice surface rises just a few centimeters. The newly recorded kilometer-wide intrusion beneath the ice could be the reason why observed ice loss in recent decades has consistently been greater than that projected by ice sheet models, the lead author said Eric Rignot, glaciologist and climate ice researcher at the University of California. , Irvine.
“The important thing about Antarctic sea ice is that since 2016 it has changed state,” he said.
Some newspapers have explained last year’s sea ice decline as an abrupt event, but Rignot has a different view.
“I consider that Antarctic sea ice has been changing very, very slowly for decades, and that it has now reached a threshold,” he said. “It’s an illustration that the Southern Ocean is changing. Remember, the loss of Antarctic sea ice since 2016 is greater than the loss of Arctic sea ice over the last 40 years combined. It’s a big problem.
Antarctic sea ice extent has not recovered much this year. February’s seasonal minimum tied with 2022 as the second lowest on record, marking three straight years of historic record extents, according to NASA, a possible sign of long-term change in the Southern Ocean.
Diamond’s sea ice modeling study also supports the idea of a major long-term change around Antarctica. She said their modeling showed that after an extreme decline like 2023, sea ice grows back, but not to what it was before.
“We saw the sea ice start to recover a little bit over the next few years,” she said. “But even after 20 years, this figure remains low. So I think that tells us that it might stay low over the next few decades, relative to what we thought.
Profound global consequences
Large changes in Antarctica’s sea ice will have a profound effect on other parts of the planet. In addition to protecting the exposed edges of Antarctica’s continental ice shelves from waves, sea ice formation acts as a driver for ocean currents and influences weather patterns in the Southern Hemisphere, the researchers said. researchers.
And because ocean water is considerably darker than ice, it absorbs much more heat. This adds to global warming and could potentially mean more relatively warm water reaching and melting the floating ice shelves of Antarctica’s vast glaciers, accelerating sea level rise. Wed. The Southern Ocean is also one of the largest carbon sinks on the planet, absorbing some carbon dioxide pollution from burning fossil fuels, but warmer waters slow this process.
The fate of ocean plankton, the base of the marine food chain, is also closely linked to the formation and extent of sea ice. Disruptions to this cycle can ripple through ecosystems, making it much harder for nesting birds to find food for their chicks and reducing concentrations of krill, the tiny floating crustaceans that feed whales in the Southern Ocean. In recent years, scientists have also documented catastrophic breeding failures in emperor penguin colonies due to low sea ice.
“2023 was a truly exceptional year for sea ice,” Diamond said, explaining the impetus for his new study. “We’ve seen record highs in recent years, but 2023 was really off the scale compared to anything we’d seen before in satellite records.”
Diamond said his modeling research also showed the importance of reducing emissions now, because when greenhouse gas concentrations in the atmosphere are at lower levels, “you don’t see such increased probabilities” of extreme sea ice loss.
There could also be other hotspots in Antarctica, leading Rignot to undertake a research trip to northeast Greenland, where glaciers similar to Thwaites’ are found. Using the same types of satellite measurements will help determine whether glaciers on the other side of the planet from Antarctica are subject to the same type of interaction with seawater that can accelerate melting.
As the tidal wave penetrates the narrow spaces between the ice bottom and the seafloor, the water it pressurizes lifts the ice surface enough to make it visible from space, a- he explained.
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“It increases by a few millimeters and we can detect it. Satellite technology is very powerful, it detects the slightest changes,” Rignot said.
A few millimeters or centimeters may not seem like much, but he said it can have a big effect: “Think about it if this happened under your house,” he said. “You don’t need to have a meter of water to worry. If it’s 5 or 10 centimeters of water coming into my house and shaking it up regularly, I don’t like that.
He said the new study into seawater intrusion should prompt a return to the isolated Thwaites Glacier to study it further, as it could potentially cause sea level rise if ice flows towards the ocean accelerated.
“We also need to study in the field, diving instruments into the ocean, to see how these things work,” he said. “We use satellites to observe the surface, but the key to understanding these processes is being able to observe it at depth. We cannot model things we cannot observe.
Bob Berwyn
Journalist, Austria
Bob Berwyn, a journalist based in Austria, has covered climate science and international climate policy for more than a decade. Previously, he reported on the environment, endangered species and public lands for several Colorado newspapers, and also worked as an editor and assistant editor at community newspapers in the Colorado Rockies.