Flying over Antarctica, it’s hard to see what all the fuss is about. Like a giant wedding cake, the snow ice on top of the world’s largest ice sheet looks soft and spotless, beautiful and perfectly white. Small swirls of snow dunes cover the surface.
But as you get closer to the edge of the ice sheet, a feeling of enormous underlying power emerges. Cracks appear on the surface, sometimes arranged like a washing table, and sometimes a complete chaos of needles and ridges, revealing the pale blue crystalline heart of the ice beneath.
As the plane flies lower, the scale of these ruptures grows steadily. It’s not just cracks, but canyons big enough to swallow a plane or monument-sized needles. Cliffs and tears emerge, tears on the white blanket, indicating a force that can throw blocks of ice out of the city like so many shattered cars in a crowd. It is a twisted, torn and broken landscape. There is also a sense of movement, in a way that no ice-free part of the Earth can convey: the whole landscape is moving, and it doesn’t seem very happy.
Broken ice where the Thwaites Glacier heads out to sea. Ted Scambos
Antarctica is a continent that includes several large islands, one the size of Australia, all buried under a 10,000-foot-thick layer of ice. The ice contains enough fresh water to raise the sea level by almost 200 feet.
Its glaciers have always been moving, but under the ice changes are taking place that have profound effects on the future of the ice sheet and the future of coastal communities around the world.
Breaking, thinning, melting, sinking
Antarctica is where I work. As a polar scientist, I have visited most areas of the ice sheet on more than 20 trips to the continent, carrying sensors and weather stations, crossing glaciers, or measuring the speed, thickness, and structure of ice.
I am currently the coordinating scientist in the United States for a major international research effort on the riskiest glacier in Antarctica, more on that in a moment. I’ve traversed crevices with caution, carefully stepped on the hard, blue ice swept by the wind, and driven for days through the most monotonous landscape imaginable.
The mountains direct the flow of glaciers into the sea. 66 North via Unsplash
For most of the last few centuries, the ice sheet has been stable, so polar science can tell. Our ability to keep track of how much ice comes out each year and how much snow falls on top dates back only a handful of decades, but what we see is a layer of ice that was almost in balance. until the 1980s.
At first, the changes in the ice occurred slowly. The icebergs would break, but the ice was replaced by a new exit. The total snowfall had not changed much for centuries, we knew this by looking at the ice cores, and in general the ice flow and the elevation of the ice sheet seemed so constant that the main goal of the first research on ice in Antarctica was to find a place, any place, that had changed drastically.
Ice breaks from the front of a glacier in Antarctica. 66 North via Unsplash A map of Antarctica seen from above, mostly from the ice sheet, shows the speed of the ice flow. Thwaites Glacier is on the left. Scientific visualization study by NASA’s Goddard Space Flight Center
But now, as the surrounding air and ocean warm, areas of the Antarctic ice sheet that have been stable for thousands of years are breaking, thinning, melting, or in some cases cases, they collapse into a pile. As these ice edges react, they send a powerful reminder: If even a small part of the ice sheet sank completely into the sea, the impact on the world’s shores would be severe.
Like many geoscientists, I think about how the Earth looks below the part we can see. For Antarctica, this means thinking about the landscape under the ice. What is the buried continent like, and how does this rocky basement shape the future of ice in a warming world?
Visualizing the world under the ice
Recent efforts to combine data from hundreds of ground and aircraft studies have given us a kind of map of the continent under the ice. It reveals two very different landscapes, divided by the trans-Antarctic mountains.
In East Antarctica, the closest part to Australia, the continent is rugged and furrowed, with several small mountain ranges. Some of them have alpine valleys, cut by the first glaciers that formed in Antarctica 30 million years ago, when their climate resembled that of Alberta or Patagonia. Most of the bedrock of East Antarctica lies above sea level. This is where the city-sized Conger ice shelf collapsed amid an unusually intense heat wave in March 2022.
Under the ice, recent studies have mapped the bedrock of Antarctica and show that much of the west side is below sea level. Bed map2; Fretwell 2013
In West Antarctica, the bedrock is very different, with much deeper parts. This area was once the bottom of the ocean, a region where the continent stretched and split into smaller blocks with deep seabeds between them. The large islands made of volcanic ridges are joined together by a thick layer of ice. But the ice here is warmer and moves faster.
Just 120,000 years ago, this area was probably an open ocean, and definitely so in the last 2 million years. This is important because our climate today is rapidly approaching temperatures like those of a few million years ago.
The fact that the ice sheet of West Antarctica had disappeared in the past is a cause for great concern in the age of global warming.
Early stages of a large-scale retreat
Towards the coast of West Antarctica is a large area of ice called the Thwaites Glacier. This is the widest glacier on earth, 70 miles in diameter, draining an area almost as large as Idaho.
Satellite data tells us that it is in the early stages of a large-scale retreat. The height of the surface has dropped to 3 feet each year. Huge cracks have formed on the shore and many large icebergs have been left adrift. The glacier flows at more than a mile a year, and that speed has almost doubled in the last three decades.
Two decades of satellite data show the fastest ice loss in the vicinity of the Thwaites Glacier. NASA. From above, fractures are evident in the Thwaites Glacier. Ted Scambos
This area was observed from the beginning as a place where ice could lose its adhesion to the bedrock. The region was called the “weak bank” of the ice sheet.
Some of the earliest measurements of ice depth, using a radio echo sounder, showed that central West Antarctica had a rock up to a mile and a half below sea level. The coastal area was shallower, with few mountains and some higher ground; but near the shore there was a great gap between the mountains. This is where the Thwaites Glacier meets the sea.
This pattern, with deeper ice piled up near the center of a layer of ice, and a shallower but still shallow rock bed near the shore, is a recipe for disaster, albeit a very slow disaster.
Ice flows by its own weight, something we learned at the Earth Science Institute, but think about it now. With very high and very deep ice near the center of Antarctica, there is huge potential for faster flow. Being shallower near the edges, the flow slows down, crushing into the bedrock as it tries to get out, and with a shorter column of ice on the shore that narrows it outward.
An Antarctic glacier flows into the sea. Erin Pettit
As the warmer water is undermining the glacier.
If the ice recedes enough, the retreating front would change from “thin” ice (still nearly 3,000 feet thick) to thicker ice toward the center of the continent. On the verge of retreat, the ice would flow faster, because now the ice is thicker. As it flows faster, the glacier pulls down the ice behind it, allowing it to float, causing more retreat. This is known as a positive feedback loop: retreat leads to thicker ice at the front of the glacier, which makes flow faster and leads to more retreat.
Hot water: The assault from below
But how would this retreat begin? Until recently, Thwaites hadn’t changed much since it was first mapped in the 1940s. At first, scientists thought a retreat would be the result of warmer air and surface melting. But the cause of the changes in Thwaites observed in the satellite data is not so easy to detect from the surface.
Under the ice, however, at the point where the ice sheet first rises from the continent and begins to protrude over the ocean like a floating ice shelf, the cause of the retreat becomes apparent. Here, ocean water well above the melting point is eroding the base of the ice, erasing it as an ice cube disappears moving in a glass of water.
The hot water reaches under the ice shelf and erodes it from below. Scambos et al 2017
Water that is capable of melting up to 50 to 100 feet of ice each year is found along the edge of the ice sheet here. This erosion allows ice to flow faster, pushing against the floating ice platform.
The ice shelf is one of the restraining forces that hold back the ice sheet. But ground ice pressure is slowly breaking this ice sheet. Like a board that breaks with too much weight, it is developing large cracks. When it yields, and the mapping of the …