Almost half of Antarctica's ice shelves have shrunk over the past 25 years

In total 71 of the 162 ice shelves surrounding the continent got smaller from 1997 to 2021

An aerial view issued by the British Antarctic Survey showing a massive crack in the Brunt Ice Shelf in Antarctica. AP

Almost half of Antarctica’s ice shelves have shrunk in the past 25 years, scientists have said, pointing to human-induced global warming as a likely cause.

A study led by researchers at Leeds University found that 71 of the 162 ice shelves that surround the continent in the southern hemisphere reduced in volume from 1997 to 2021, releasing 7.5 trillion tonnes of meltwater into the oceans.

Almost all the ice shelves on the western side of Antarctica, which is exposed to warm water, got smaller, while those on the more protected eastern side stayed the same size or increased in volume, it said.

Over the past 25 years, 67 trillion tonnes of ice was released into the ocean, while 59 trillion tonnes of ice was added to the shelves, with a net loss of 7.5 trillion tonnes.

“There is a mixed picture of ice-shelf deterioration, and this is to do with the ocean temperature and ocean currents around Antarctica,” said Dr Benjamin Davison, a research fellow at the University of Leeds, who led the study which was published in the journal Scientific Advances.

“The western half is exposed to warm water, which can rapidly erode the ice shelves from below, whereas much of East Antarctica is currently protected from nearby warm water by a band of cold water at the coast.”

Antarctica, the world’s fifth largest continent, is about 50 times the size of the UK.

Researchers analysed more than 100,000 satellite radar images as part of the study to assess the health of its ice shelves.

On the western side of Antarctica, water temperature at the sea floor is approaching 2C, warm enough to melt the ice that is flowing on top of it. Sea temperatures on the eastern flank are colder. Photo: Dr Benjamin Davison/University of Leeds

Any shrinkage of the ice shelves will have a major knock-on effect on the global ocean circulation, the giant “conveyor belt”, which moves nutrients as well as heat and carbon from this sensitive polar ecosystem as dense salty water sinks to the ocean floor.

Freshwater melt from ice dilutes the salty ocean water, making it fresher and lighter, which takes longer to sink, weakening the ocean circulation system – a process a recent study found may already be under way.

‘No sign of recovery’

The seas on the western side of Antarctic experience different currents and winds than the east, in a process that is driving warmer water underneath the ice shelves on the western flank.

“We expected most ice shelves to go through cycles of rapid, but short-lived shrinking, then to regrow slowly. Instead, we see that almost half of them are shrinking with no sign of recovery,” said Dr Davison, who is an expert in earth observation of the polar regions.

Human-induced global warming is likely to be a key factor in the loss of the ice, he said, adding that if it was due to natural variation in climate patterns, there would have been some signs of ice regrowth on the western ice shelves.

Ice shelves, which float on the seas surrounding Antarctica, act as giant “plugs” at the end of glaciers, slowing down the flow of ice draining into the oceans.

If they weaken or reduce in size, the rate of ice lost from the glaciers increases.

The Getz Ice Shelf, where 1.9 trillion tonnes of ice were lost over the 25-year study period, saw some of the largest losses. The vast majority of that loss was due to melting at the base of the ice shelf, with just 5 per cent due to calving, when large chunks of ice break away from the shelf and move into the ocean.

A large iceberg near the island of South Georgia, in the South Atlantic, where it floated from Antarctica, after calving from the Larsen C ice shelf in July 2017. EPA

Around one third of the 1.3 trillion tonnes of ice lost on the Pine Island Ice Shelf was due to calving, with the rest caused by melting from the underside of the ice shelf.

In contrast, the Amery Ice Shelf, on the east side of Antarctica, actually gained 1.2 trillion tonnes of ice because it is surrounded by much colder waters.

“The study has generated important findings. We tend to think of ice shelves as going through cyclical advances and retreats. Instead, we are seeing a steady attrition due to melting and calving,” said Professor Anna Hogg, who is also from the University of Leeds and a co-author of the study.

“Many of the ice shelves have deteriorated a lot: 48 lost more than 30 per cent of their initial mass over just 25 years.

“This is further evidence that Antarctica is changing because the climate is warming.

“The study provides a baseline measure from which we can see further changes that may emerge as the climate gets warmer.”