Scientists identify new Antarctic ice sheet ‘tipping point,’ warning future sea level rise may be underestimated

By Laura Paddison, CNN

CNN  —  The Antarctic ice sheet is melting in a new, worrying way that scientific models used to project future sea level rise have not taken into account, suggesting current projections could be significantly underestimating the problem, according to a new study.

Scientists from the British Antarctic Survey found that warm ocean water is seeping beneath the ice sheet at its “grounding line” — the point at which the ice rises from the seabed and starts to float — causing accelerated melting which could lead to a tipping point, according to the report published Tuesday in the journal Nature Geoscience.

A tipping point refers to the threshold at which a series of small changes accumulate to push a system beyond a point of no return.

The melting works like this: relatively warm ocean water opens cavities in the ice, allowing more water to seep in, which causes more melting and larger cavities to form, and so on.

A small increase in ocean temperatures can have a very big impact on the amount of melting, the study found. As climate change heats up the oceans, the process speeds up.

“You get this kind of runaway feedback,” said Alex Bradley, an ice dynamics researcher at BAS and lead author of the paper. It behaves like a tipping point, he told CNN, “where you can have a very sudden shift in how much melting is happening in these places.”

This tipping point would play out through a faster flow of ice into the oceans, in a process not currently included in models of future sea level rise, Bradley said, suggesting “our projections of sea level rise might be significant underestimates,” he added.

The implications wouldn’t be felt immediately, according to the study, but would see a higher rise in sea levels accumulating over tens and hundreds of years, threatening coastal communities around the world.

The study does not give time frames for when the tipping point might be reached, nor does it give figures for how much sea level rise can be expected. But the region is hugely significant: the Antarctic ice sheet already sheds an average of 150 billion metric tons of ice every year and, in its entirety, it holds enough water to raise global sea levels by around 190 feet (around 58 meters).

The study is not the first to point to Antarctica’s vulnerabilities to the climate crisis. A slew of research points to the vulnerability of West Antarctica in particular, especially the Thwaites Glacier, known as the Doomsday Glacier for the catastrophic impact it could have on sea level rise.

But what surprised Bradley about this study, which used climate modeling to understand how this melting mechanism could affect the whole ice sheet, is that some of the most vulnerable glaciers were those in East Antarctica.

Icebergs in Antarctica on February 8, 2024. A slew of research has looked at the vulnerability of this vast continent to the impacts of the climate crisis.

Eric Rignot, professor of Earth system science at the University of California at Irvine, who was not involved in the research, told CNN the study “encourages us to take a closer look at physical processes taking place in grounding zones.”

“But this is a very complex, poorly observed region and a lot more research and field observations are needed,” he cautioned, including establishing what processes control the intrusion of ocean water beneath the ice and exactly how this affects the ice melting.

Recent research from West Antarctica found melting at the base of glaciers was actually lower than expected, because it was being suppressed by a layer of colder, fresher water — although scientists still found a rapid retreat.

Ted Scambos, a glaciologist at the University of Colorado Boulder, said the new model developed by the BAS scientists “is potentially very important” but it should be looked at together with more recent findings, including mechanisms of ice melt as well as the impacts tides have on pumping seawater beneath the ice.

Bradley hopes the study will prompt more research into which regions might be most at risk and will give added impetus for policies to tackle the climate crisis. “With every small increase in ocean temperature, with every small increase in climate change, we get closer to these tipping points,” he said.

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