Melting Ice Shelves

Ice shelves are the floating edges of the Antarctic Ice Sheet.

Antarctic ice shelves have been in steady decline for 25 years, and the rate of melt is increasing.

Ice shelves are a critical line of defense against the melting of the Antarctic Ice Sheet and rapid sea level rise.

West Antarctic ice shelves are rapidly melting, and research is increasingly pointing to a link with climate change caused by human activity.

Ice shelves are floating glaciers – the outer edges of the Antarctic Ice Sheet. There are approximately 300 ice shelves around Antarctica. Together they cover around three quarters of the Antarctic coastline – roughly the same area as the entire Greenland Ice Sheet.

The larger Antarctic ice shelves are the size of small nations and over a hundred feet thick. The largest ice shelf on earth, the Ross Ice Shelf, is almost as large as France. It terminates in an ice cliff more than 370 miles (600 kilometers) long, towering up to 160 feet (150 meters) above the ocean.

ICE SHELVES

Antarctica’s ice shelves are shrinking

Every year for the past 25 years, Antarctic ice shelves have been losing mass. Many of them are becoming thinner, smaller and more vulnerable to sudden collapse on a large scale.

Strong winds around Antarctica are driving warmer currents to the edge of the continent.

On the Antarctic Peninsula, the ice is melting not only from below but also above.

Buttressing schematic — Image credit: Ronja Reese & Maria Zeitz

Collapsing ice shelves don’t contribute directly to rising sea levels because they are already floating on the ocean, but they do offer a critical line of defense. Ice shelves act as a brake for the glaciers that make up the Antarctic Ice Sheet. When ice shelves melt the glaciers behind them soon follow, contributing directly to sea level rise.

Ice shelves slow the flow of the ice sheet by pushing back against the glaciers that feed them, helping to slow their flow by acting as a buttress, or a braking system for the ice. As ice shelves flow out over bays and inlets they may run into obstacles, such as peninsulas, islands or ice rises. These ’pinning points’ obstruct the flow of the ice shelf and slow it down.

As the ice shelf continues to push against these features, pressure builds up. This pressure is transferred back against the ice sheet, restricting its flow. When ice shelves break apart, this backward pressure is released and glaciers can flow unrestrained into the sea.

Image credit: A. J. Cook and D. G. Vaughan

The collapse of Larsen B

The Larsen Ice Shelf extends along the east coast of the Antarctic Peninsula and flows east over the Weddell Sea. It is the northernmost ice shelf in Antarctica, and includes seven distinct sectors named A to G. Larsen A collapsed in 1995, having been in place for 4,000 years.

When the Larsen B sector collapsed in February 2002 it was the largest and most rapid event of its kind scientists had ever seen. In one month, a part of the Larsen B sector covering 1,250 square miles (3,250 sq km) – an area roughly the same size as Yosemite National Park – broke away from the shelf. The ice shelf had been in place since the last glacial period 10,000 years ago.

Antarctic Peninsula ice flow. Image credit: European Space Agency

After this partial collapse, scientists reported that sections of the glacier flowing down behind the collapsed part of the shelf sped up as much as eightfold – the equivalent of a car accelerating from 55 to 440 mph. The ice shelf had been serving as a ‘brake’ on the flow of the ice behind it, and without it the glacier was free to flow into the sea.

The Antarctic Peninsula is warming faster than any other part of Antarctica. In fact, it is one of the fastest-warming places in the Southern Hemisphere. The extensive Larsen B calving event is thought to have been accelerated by warm summer temperatures and warm ocean currents melting the ice from below.

Prior to collapse, the Larsen B Ice Shelf covered 1,250 square miles (3,250 square kilometers) and was around 220m thick (720 feet).

Video credit: NASA

map of Amundsen Sea — Image credit: Polargeo

Thwaites Glacier, West Antarctica

At around 980 feet (300 meters) thick, the Thwaites Ice Shelf is one of the biggest ice shelves in West Antarctica: roughly the size of Florida. In the 1990s Thwaites was losing just over 10 billion tons of ice a year. By 2020 it was more like 80 billion tons, an eightfold increase in less than 30 years. Most of this has been attributed to warm ocean currents melting the ice from underneath.

The Thwaites Glacier has been described by some researchers as a ‘cork in a bottle’. It lies at the heart of the West Antarctic Ice Sheet, a region particularly vulnerable to rapid melting due to the shape of the land under the ice. The instability of the ice in this region means that if ice in the region continues to melt rapidly, it could reach irreversible tipping points without warning.

The instability of the ice in this region means that if the Thwaites Glacier continues to melt rapidly, it could reach irreversible tipping points without warning. This glacier alone could contribute one to two feet of global sea level rise in as little as 50 to 100 years. If it melted completely, which some researchers believe could happen in centuries, the surrounding glaciers are likely to follow. This could eventually lead to the collapse of the entire West Antarctic Ice Sheet and over 10 feet of sea level rise.

Thwaites and its neighboring glaciers are of particular concern to researchers due to marine ice sheet instability, which could make the region particularly vulnerable to sudden, rapid melting.

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