Antarctica’s vast ice fields and the floating sea ice that surrounds the continent are Earth’s largest heat shields, reflecting solar radiation away from the planet. Two studies released today show how global warming is penetrating even the sunlight reflector in the coldest region on Earth.
Research by scientists from the British Antarctic Survey focused on last year’s staggering decline in sea ice. During the austral winter of 2023, Antarctic sea ice extent was about 770,000 square kilometers below average, an area larger than Alaska.
Lead author Rachel Diamond said the modeling study showed such an extreme decline would be a one-in-2,000-year event without climate change, “which tells us the event was very extreme,” she said. “Anything less than one in a hundred 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 the glacier’s melt and contributing to its rise of sea level.
“The intrusion of pressurized seawater will trigger powerful melting of the grounded ice for kilometers, making the glacier more vulnerable to ocean warming and increasing predictions of ice mass loss,” the authors wrote in the paper, published in the Proceedings of the National Academy of Sciences. .
“The concern is that we are underestimating the rate at which the glacier is changing, which would be devastating to coastal communities around the world,” said co-author Christine Dow, professor in the Faculty of Environment at the University of Waterloo in Ontario, Canada.
In that study, scientists tracked the course of seawater by analyzing data from sensitive radar instruments that can detect when the surface of the ice rises just a few centimeters. The newly recorded mile-wide intrusion under the ice may be the reason observed ice loss in recent decades has been consistently greater than what is projected by ice sheet models, says lead author Eric Rignot, a glaciologist and climate ice researcher at the University of California. , Irvine.
“The most important thing about the Antarctic sea ice is that it has changed state since 2016,” he says.
Some papers have explained last year’s sea ice decline as an abrupt event, but Rignot has a different perspective.
“I think of it as Antarctic sea ice that has been evolving very, very slowly for decades, and has now reached a threshold,” he said. “It is an illustration that the Southern Ocean is changing. Consider that the loss of Antarctic sea ice since 2016 is greater than the loss of Arctic sea ice in the past forty years combined. It’s quite a big deal.”
The extent of Antarctic sea ice has not recovered much this year. February’s seasonal minimum tied 2022 as the second-lowest on record, marking three straight years of record lows, according to NASA, a possible sign of a long-term shift in the Southern Ocean.
The sea ice modeling research led by Diamond also supports the idea of a major long-term shift around Antarctica. She said their models show that sea ice will grow back after an extreme drop like the one in 2023, but not to what it was before.
“We found that the sea ice begins to recover somewhat in subsequent years,” she said. “But even after twenty years it is still low. So I think this tells us that it could remain low for decades to come, compared to where we thought it would be.”
Profound global implications
Major changes in Antarctic 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 of ocean currents and influences weather patterns in the Southern Hemisphere, the researchers said.
And because open ocean water is significantly darker than ice, it absorbs much more heat. That contributes to the planet’s overall warming, and could potentially mean more relatively warm water reaching and melting the floating ice shelves of Antarctica’s massive glaciers, which would accelerate sea level rise. The Southern Ocean is also one of the largest carbon sinks on Earth, absorbing some of the carbon dioxide pollution from the burning of fossil fuels, but warmer water slows that process.
The fate of ocean plankton, at the base of the marine food chain, is also closely linked to the formation and extent of sea ice. Disruptions to that cycle can ripple through ecosystems, making it much harder for breeding birds to find food for their chicks and reducing concentrations of krill, the small floating crustaceans that whales feed on in the Southern Ocean. In recent years, scientists have also documented catastrophic breeding failures of emperor penguin colonies due to low sea ice.
“2023 was such an exceptional year for sea ice,” Diamond said, explaining the impetus for her new research. “We’ve seen record lows in recent years, but 2023 was really so off scale compared to anything we’ve seen before in the satellite records.”
Diamond said her modeling study also showed the importance of cutting emissions now, because when concentrations of greenhouse gases in the atmosphere are at lower levels, “you don’t see such an increase in the chances” of extreme sea ice loss.
There may also be other problem areas in Antarctica, prompting Rignot to make a research trip to northeastern Greenland, where there are glaciers similar to those of Thwaites. Using the same types of satellite measurements will help determine whether the glaciers on the other side of the planet, from Antarctica, are subject to the same types of interactions with seawater that could accelerate melting.
As the tidal wave enters narrow gaps between the bottom of the ice and the seafloor, the water it pressurizes raises the surface of the ice enough to make it visible from space, he said.
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“It goes up by millimeters and we can find out. The satellite technology is very powerful and detects the smallest changes,” says Rignot.
A few millimeters or centimeters may not sound like much, but he said it can have a big impact. “Think about this if this happened under your house,” he said. “You don’t need a meter of water to worry. If 2 or 4 inches of water comes into my house and it shakes regularly, I don’t like it.”
He said the new research into seawater intrusion should lead to a return to the remote Thwaites Glacier to study it further, as it has the potential to cause sea level rise if the ice flowing into the ocean flows faster.
“We also need to study on the ground and dip instruments in the ocean to see how these things work,” he said. “We use satellites to see the surface, but the key to understanding these processes is to be able to observe it at depth. We can’t model things we can’t observe.”
Bob Berwyn
Reporter, Austria
Bob Berwyn, an Austria-based reporter who has covered climate science and international climate policy for more than a decade. He previously 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.