A ‘triple whammy’ of chaos has triggered a downward spiral in Antarctica, scientists discover

By Laura Paddison, CNN

(CNN) — For decades, it seemed Antarctica might be insulated from the kind of rapid ice melting unfolding in the Arctic. But in 2015, that changed when the sea ice fringing this vast, icy continent stopped expanding and began to decline dramatically. Now, scientists say they have figured out why this happened — and their findings spell deep trouble for a region whose fate affects us all.

Antarctic sea ice has been on a steep downward trend for nearly a decade. It reached a record low in 2022 and again in 2023, when it dropped to just 691,000 square miles, equivalent to an area of missing ice larger than Greenland compared to average levels. This year saw a higher amount of sea ice at the height of the Southern Hemispher summer, but it was still at its 16th lowest level in nearly five decades of record keeping.

Scientists have been working for years to understand what is driving the precipitous decline in sea ice and whether it is a sign Antarctica is entering a new state.

The new research identifies a series of different processes — driven by intensifying winds and warming water — which flipped the ocean surrounding Antarctica “out of balance.” It amounts to a “triple whammy of climate chaos,” the report authors wrote in a press release accompanying the paper, which was published in the journal Science Advances on Friday.

The chain of events began decades ago, when westerly winds around Antarctica started to get stronger, said Aditya Narayanan, a study author and research fellow in physical oceanography at the University of Southampton in the UK.

The strength of these winds has been linked, in part, to the increase of planet-heating pollution from burning fossil fuels, as well as the hole in the ozone layer above the continent.

These winds initially helped cool the surface ocean, but this changed over time as a slower, deeper response took hold. From around 2015, the winds started dragging up relatively warm, salty water from the ocean depths to the surface. The heat melted sea ice, and more salt at the surface made the water denser, affecting the way the ocean layers mixed and making it easier for more heat to move upward.

Around 2018, after a few years of declining sea ice, a third phase kicked in, according to the research. The region became trapped in a cycle where less sea ice meant water at the ocean surface remained salty and warm, which in turn prevented more ice forming.

“These three phases show how long-term changes driven by climate change can trigger a cascade of processes that push the system toward a prolonged state of low sea ice,” Narayanan said.

The study noted there were differences between East Antarctica, where sea ice retreat has largely been triggered by heat rising from the deeper ocean, and West Antarctica, where the atmosphere has played a larger role, as clouds carried by warm air help trap heat near the ocean surface.

The loss of sea ice has wide ripple effects. As it disappears, it leaves coastal ice sheets and glaciers exposed to waves and warmer ocean waters, making them much more vulnerable to melting and breaking up.

Sea ice also acts like a giant mirror reflecting the sun’s energy away from the Earth and back into space. When it melts, it exposes the darker ocean beneath which absorbs the sun’s energy, increasing warming.

Loss of sea ice could also destabilize currents that store heat and carbon in the ocean, accelerating global warming, the scientists said.

The paper offers a good insight into what’s happening in Antarctica, said Oscar Schofield, a biological oceanographer at Rutgers University, who was not involved in the study.

Clarifying the drivers of sea ice loss “will help us understand why things are changing and potentially forecast the future with more confidence,” he told CNN. There is still debate about what that future holds for Antarctica, but “the observed declines are stunning,” he added.

Ted Scambos, senior research scientist for the Earth Science and Observation Center at the University of Colorado Boulder, said the study creates a “more coherent story for the past 10 years of Antarctic sea ice extent changes.” Looking forward, said Scambos who was not involved in the research, “I agree that it is unlikely that Antarctic sea ice can recover.”

If low sea ice persists into 2030 and beyond, the impacts could be enormous, said Alberto Naveira Garabato, a report author and physical oceanographer at the University of Southampton, “The ocean may transition from a stabilizer of the world’s climate to a powerful new driver of global warming.”

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