Our biggest glacier problem is melting from the bottom-up

Our biggest glacier problem is melting from the bottom-up thumbnail
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This article was originally featured on The Conversation.

Flying over Antarctica, it’s difficult to see the point of all the excitement. The frosting of snow that covers the largest ice sheet in the world looks like a huge wedding cake. It is smooth, unblemished, beautiful, and perfectly white. The surface is covered in little snow dunes.

As you approach the edge, you feel a sense of immense underlying power. Cracks begin to appear on the surface, sometimes appearing like a washboard and sometimes as a chaotic mess of spires or ridges. These cracks reveal the pale blue crystalline heart beneath the ice.

As the plane flies lower the scale of these cracks steadily increases. These cracks are not just cracks. They can also create canyons large enough for a jetliner to be swallowed, or spires that are the size of monuments. There are tears and cliffs, as well as tears and rips in the blanket, which indicate a force that can toss city blocks full of ice around like a pileup of wrecked cars. It’s a torn, twisted, and wrenched landscape. It also conveys a sense of movement that no ice-free area of the Earth can convey. The entire landscape is in motion and appears not to be happy about it.

Antarctica is a continent comprising several large islands, one of them the size of Australia, all buried under a 10,000-foot-thick layer of ice. The ice holds enough fresh water to raise sea level by nearly 200 feet.

Its ice glaciers have been moving for centuries, but below the ice, there are changes that are having profound effects on the future ice sheet and coastal communities all over the globe.

Breaking, thinning, melting, collapsing

Antarctica is where you work. As a polar scientist I’ve visited most areas of the ice sheet in more than 20 trips to the continent, bringing sensors and weather stations, trekking across glaciers, or measuring the speed, thickness and structure of the ice.

Currently, I am the U.S. coordinator scientist for an international research effort to study Antarctica’s most dangerous glaciers. More details will follow. I have walked for days across the most boring landscapes, climbed over crevasses and trod carefully on hard blue windswept glaciers.

For most of the last few centuries, the ice sheets has been stable as far as polar science is concerned. Our ability to track how much ice flows out each year, and how much snow falls on top, extends back just a handful of decades, but what we see is an ice sheet that was nearly in balance as recently as the 1980s.

Early on, the ice was changing slowly. The icebergs would eventually break apart, but new outflow would replace it. Total snowfall had not changed much in centuries-this we knew from looking at ice cores-and in general the flow of ice and the elevation of the ice sheet seemed so constant that a main goal of early ice research in Antarctica was finding a place, any place, that had changed dramatically.

Our biggest glacier problem is melting from the bottom-up
A map of Antarctica seen from above, most of it the ice sheet, shows the velocity of the ice flow ice. Thwaites Glacier can be seen to the left. NASA’s Goddard Space Flight Center Scientific Visualization Studio

But now, as the surrounding air and ocean warm, areas of the Antarctic ice sheet that had been stable for thousands of years are breaking, thinning, melting, or in some cases collapsing in a heap. These ice edges are a powerful reminder that if any part of the Antarctic ice sheet was to collapse into the ocean, it would have a devastating impact on the world’s coastlines.

I think about the Earth below what we can see. That means that Antarctica must be viewed from below the ice. What does the buried continent look and how does that rocky basement influence the future of ice in a warming world.

Visualizing the world below the ice

Recent efforts to combine data from hundreds of airplane and ground-based studies have given us a kind of map of the continent below the ice. This map shows two very different landscapes that are separated by the Transantarctic Mountains.

In East Antarctica, the part closer to Australia, the continent is rugged and furrowed, with several small mountain ranges. Some of these have alpine valleys, cut by the very first glaciers that formed on Antarctica 30 million years ago, when its climate resembled Alberta’s or Patagonia’s. The majority of East Antarctica’s bedrock is above sea level. This is where the city-size Conger ice shelf collapsed amid an unusually intense heat wave in March 2022.

In West Antarctica, the bedrock is very different with deeper parts. This was the ocean bottom. It was a region in which the continent was once stretched out and then broken down into smaller blocks with deep seabed. The thick blanket of ice links large islands made from volcanic mountain ranges. However, the ice is moving faster and warmer here.

As recently as 120,000 years ago, this area was probably an open ocean-and definitely so in the past 2 million years. This is important because our climate today is fast approaching temperatures like those of a few million years ago.

The realization that the West Antarctic Ice Sheet is gone in the past is a cause for concern in the current global warming era.

Early stages of a large-scale retreat

Toward the coast of West Antarctica is a large area of ice called Thwaites Glacier. This is the widest glacier on earth, at 70 miles across, draining an area nearly as large as Idaho.

Satellite data tell us that it is in the early stages of a large-scale retreat. Each year, the surface height has been falling by as much as 3 feet. At the coast, large cracks have formed and many large icebergs were set adrift. The glacier flows at more than a mile per annum, and this speed has almost doubled over the past three decades.

YouTube video

This area was noted early on as a place where the ice could lose its grip on the bedrock. The region was termed the “weak underbelly” of the ice sheet.

Some of the first measurements of the ice depth, using radio echo-sounding, showed that the center of West Antarctica had bedrock up to a mile and a half below sea level. The coast was shallower with a few hills and higher ground, but there was a large gap between the mountains near the coast. This is where Thwaites Glacier meets with the sea.

This pattern with deeper ice piled high at the center of an Ice Sheet and shallower, but still low, bedrock near the coast is a recipe to disaster, although it’s a slow-moving one.

Ice flows below its own weight-something that we learned in high school earth sciences, but it is worth a second thought. There is tremendous potential for faster flow with very tall and deep ice near Antarctica’s center. The flow is held back by being shallower at the edges. It grinds on the bedrock and squeezes it outward.

YouTube video

If the ice were to step back far enough, the retreating front would go from “thin” ice-still nearly 3,000 feet thick-to thicker ice toward the center of the continent. Because the ice is thicker, the ice would flow quicker at the retreating edge. The glacier’s faster flow allows the ice to slide behind it, which causes more retreat. This is what’s known as a positive feedback loop-retreat leading to thicker ice at the front of the glacier, making for faster flow, leading to more retreat.

Warming water: The assault from below

How would this retreat start? Until recently, Thwaites had not changed a lot since it was first mapped in the 1940s. Early on, scientists thought a retreat would be a result of warmer air and surface melting. It is difficult to see the reason for Thwaites’ changes in satellite data.

Beneath the ice, however, at the point where the ice sheet first lifts off the continent and begins to jut out over the ocean as a floating ice shelf, the cause of the retreat becomes evident. Here, ocean water well above the melting point is eroding the base of the ice, erasing it as an ice cube would disappear bobbing in a glass of water.

Water that is capable of melting as much as 50 to 100 feet of ice every year meets the edge of the ice sheet here. This allows the ice to flow faster and pushes against the floating ice shelf.

The ice shelf is one of restraining forces that holds back the ice sheet. But pressure from the land ice is slowly breaking this ice plate. It is breaking down like a board that has become brittle from too much weight. It will eventually give way. The mapping of the fractures, speed of flow and the time it took to map them suggests that this is only a matter of years away . This will allow the ice flow faster, thereby feeding the feedback loop.

Up to 10 feet of sea level rise

Looking back from our camp this summer at the ice-covered continent, it is a sad sight. The coast is dominated by a huge glacier that flows toward the coast and extends from horizon to shore to the West Antarctic Ice Sheet. It is clear that the ice is bearing down on this coast.

Ice is still ice-it doesn’t move that fast no matter what is driving it; but this giant area called West Antarctica could soon begin a multicentury decline that would add up to 10 feet to sea level. The rate of sea level rising would rise severalfold, creating significant challenges for coastal residents. This is true for almost everyone.

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