More than 40% of Antarctica’s ice shelves have dwindled in the past 25 years, potentially accelerating sea-level rise by allowing more land ice to flow into the ocean, according to new research released Thursday. The extent of ice shelves thinning is more widespread than previously thought, the results show, providing increasing evidence that the continent is feeling the effects of higher global temperatures.

“The surprising result to me was just how many ice shelves are deteriorating that substantially and continuously,” said Benjamin Davison, lead author of the study. “Lots of ice shelves, not just the big ones, are steadily losing mass over time with no sign of recovery.”

Ice shelves are massive floating sections of ice extending from glaciers on land. They play a critical role in slowing the flow of ice on land into the ocean by essentially acting as a wall and surrounding nearly the entire coastline of Antarctica. When ice shelves thin or retreat, ice on the land can flow into the ocean more quickly and accelerate sea-level rise. The Antarctic and Greenland ice sheets are responsible for more than one-third of the total sea-level rise in recent decades.

Analyzing more than 100,000 satellite images from 1997 to 2021, Davison and his colleagues found that 71 of the 162 ice shelves surrounding Antarctica reduced in volume. Almost 50 lost more than 30 percent of their initial mass during those years. The team also found 29 shelves gained mass during the study period and an additional 62 did not change mass significantly.

Healthy ice shelves naturally retreat and grow over time, said Davison, a researcher at the University of Leeds. An ice shelf is continuously flowing and advancing but will also lose mass through melting or calving, which is when its front breaks off into the ocean. Then it can gain ice from the land and grow again.

But the large portion of steadily shrinking ice shelves shows this natural cycle is off, Davison said.

“We’re just seeing them get smaller and smaller and smaller for 25 years … often with no sign of any advance or growth in that time,” Davison said. “That’s not consistent with what we expect from the natural cycle of an ice shelf.”

The largest portion of shrinking ice shelves was found on the western side of Antarctica, where warmer water can erode the shelves from underneath. Nearly all the ice shelves on the western side experienced ice loss.

In West Antarctica, the Getz Ice Shelf experienced some of the biggest ice losses, shedding 1.9 trillion tons of ice over the study period – almost exclusively because of melting at the shelf’s base. The Pine Island Ice Shelf lost 1.3 trillion tons of ice, with a third due to calving.

Most ice shelves in East Antarctica, however, increased in volume or stayed the same. The east, Davison said, is not as exposed to the warm water as the other side of the continent. The region is protected by a band of cold water at the coast, which helps keep nearby warm water at bay. Even so, the study still showed pockets of shrinking ice shelves, and researchers are still investigating the reasons. One theory, Davison said, is that the warmer water on the western side could be slowly intruding on the region.

One of the most recent ice shelf collapses occurred in East Antarctica in March 2022. The Conger Ice Shelf – about the size of New York City – completely collapsed in the span of a few weeks, probably triggered by a record heat wave in Antarctica that proved to be the most intense ever in the world.

The thinning of the ice shelves has shown up in the surrounding environment, too. Over the 25-year study period, the team estimated, 66.9 trillion tons of fresh water from the ice shelves entered the ocean. The freshwater can dilute the saltier ocean water and make it lighter, weakening ocean circulation – a change that researchers have already observed around Antarctica.

Ice scientist Alex Gardner, who was not involved in the research, said the study’s results confirm previous work looking at ice shelf changes, including his own. His previous work found calving has increased and caused ice shelves to lose more mass into oceans. The new study also complemented another study that showed how widespread ice shelf thinning was across the continent.

“We now have multiple groups coming to the same conclusion that when you zoom out and look at the Antarctic ice shelves in their entirety, you see clear signals of retreat and thinning, signals [that] are expected in a warming world,” Gardner said.

Davison said the current ice shelf data set is not long enough for researchers to definitively make a climate change connection yet, but he said it would be a “remarkable coincidence” if the natural variability in ice shelves were just that much larger. Additionally, climate models predict ice shelves will steadily shrink in a warming world as observed, eventually hitting a tipping point that could lead to a millennial period of ice sheet disintegration.

But, Davison said, we don’t need to hit that tipping point before seeing an effect on the planet.

“The changes are big and substantial, even if (you) could imagine an even worse scenario,” Davison said. “You don’t need every ice shelf to be gone or disappearing for it to matter.”

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