Newly identified tipping point for ice sheets could mean more sea level rise

A newly identified tipping point for the loss of ice sheets in Antarctica and elsewhere could mean that future sea-level rise is significantly higher than current projections.

A new study has examined how warming seawater intervenes between coastal ice sheets and the land on which they rest. The warm water melts the cavities in the ice, allowing more water to flow in, expanding the cavities further in a feedback loop. This water then lubricates the falling ice in the ocean, pushing up the sea level.

The researchers used computer models to show that a “very small increase” in incoming water temperature can lead to a “very large increase” in ice loss—ie, tipping point behavior.

It is not known how close the tipping point is, or whether it has already been passed. But the researchers said it could be caused by temperature increases of only tenths of a degree, and more likely by expected increases in the coming decades.

Sea level rise is the biggest long-term impact of the climate crisis and is set to redraw the world map in the coming centuries. It has the potential to place many major cities, from New York City to Shanghai, below sea level and affect billions of people.

The study addresses a key question of why current models underestimate sea levels seen in earlier periods between ice ages. Scientists believe that some processes of ice sheet melting should not yet be included in the models.

“[Seawater intrusion] it could essentially be the missing piece,” said Dr Alexander Bradley of British Antarctica, who led the research. “We don’t have many other good ideas. And there’s a lot of evidence that when you include it, the amount of sea level rise that the models predict could be much, much higher.”

Previous research has shown that seawater intrusion can double the rate of ice loss from some Antarctic ice shelves. There is also real-world evidence that seawater intrusion is causing the melt today, including satellite data showing decreases in the height of ice sheets near landfall areas.

“With every tenth of a degree of ocean warming, we get closer and closer to passing that tipping point, and every tenth of a degree is related to the amount of climate change that’s happening,” Bradley said. “So we need very dramatic action to limit the amount of warming that occurs and prevent this tipping point from being passed.”

The most important action is to reduce the burning of fossil fuels to net zero by 2050.

Bradley said: “Now we want to decide [seawater intrusion] in ice sheet models and see if this doubling of sea level rise will work when analyzing all of Antarctica.

Scientists warned in 2022 that the climate crisis had brought the world to the brink of multiple “catastrophic” tipping points, including the collapse of the Greenland ice cap and the collapse of a key current in the North Atlantic, cutting off the rains on which billions of people depend . for food.

Research in 2023 found that accelerated melting of ice in West Antarctica was inevitable for the rest of the century, regardless of how much carbon emissions are cut, with “dire” implications for sea levels.

The new research, published in the journal Nature Geoscience, found that some Antarctic ice sheets were more vulnerable to seawater intrusion than others. Pine Island Glacier, currently Antarctica’s biggest contributor to sea level rise, is particularly vulnerable, as the base of the glacier slopes inland, meaning gravity helps seawater seep in. The huge Larsen Ice Sheet is also at risk.

The so-called “Doomsday” glacier, Thwaites, was found to be among the least vulnerable to seawater intrusion. This is because the ice is flowing into the sea so quickly that any cavities in the ice melted by the intrusion of seawater are quickly filled with new ice.

Dr Tiago Segabinazzi Dotto, of the UK’s National Oceanography Centre, welcomed the new analysis of the ocean-ice feedback loop beneath the ice sheets.

“The researchers’ simplified model is useful for showing this reaction, but a more realistic model is much needed to assess positive and negative reactions,” he said. “Improving observations in the grounding area is also essential to better understand the key processes associated with ice shelf instability.”