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maltatoday | SUNDAY • 12 JUNE 2022 14 EYEWITNESS Ted Scambos Ice world: Antarctica's riskiest glacier is under assault from below and losing its grip FLYING over Antarctica, it's hard to see what all the fuss is about. Like a gigantic wedding cake, the frosting of snow on top of the world's largest ice sheet looks smooth and unblemished, beautiful and perfectly white. Little swirls of snow dunes cover the surface. But as you approach the edge of the ice sheet, a sense of tre- mendous underlying power emerges. Cracks appear in the surface, sometimes organized like a washboard, and sometimes a complete chaos of spires and ridges, revealing the pale blue crystalline heart of the ice below. As the plane flies lower, the scale of these breaks steadily grows. These are not just cracks, but canyons large enough to swallow a jetliner, or spires the size of monuments. Cliffs and tears, rips in the white blanket emerge, indicating a force that can toss city blocks of ice around like so many wrecked cars in a pileup. It's a twisted, torn, wrenched landscape. A sense of movement also emerges, in a way that no ice-free part of the Earth can convey – the en- tire landscape is in motion, and seemingly not very happy about it. Antarctica is a continent com- prising 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 glaciers have always been in motion, but beneath the ice, changes are taking place that are having profound effects on the future of the ice sheet – and on the future of coastal communi- ties around the world. Breaking, thinning, melting, collapsing Antarctica is where I 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, thick- ness and structure of the ice. Currently, I'm the U.S. coor- dinating scientist for a major international research effort on Antarctica's riskiest glacier – more on that in a moment. I have gingerly crossed crevasses, trodden carefully on hard blue windswept ice, and driven for days over the most monotonous landscape you can imagine. For most of the past few centu- ries, the ice sheet has been stable, as far as polar science can tell. 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 re- cently as the 1980s. Early on, changes in the ice happened slowly. Icebergs would break away, but the ice was re- placed by new outflow. Total snowfall had not changed much in centuries – this we knew from looking at ice cores – and in gen- eral the flow of ice and the ele- vation of the ice sheet seemed so constant that a main goal of ear- ly ice research in Antarctica was finding a place, any place, that had changed dramatically. 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. As these edges of the ice react, they send a powerful re- minder: If even a small part of the ice sheet were to completely crumble into the sea, the impact for the world's coasts would be severe. Like many geoscientists, I think about how the Earth looks below the part that we can see. For Antarctica, that means thinking about the landscape below the ice. What does the buried con- tinent look like – and how does that rocky basement shape the future of the 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. It reveals two very different landscapes, divided by the Transantarctic Mountains. In East Antarctica, the part closer to Australia, the continent is rugged and furrowed, with several small mountain rang- es. Some of these have alpine valleys, cut by the very first gla- ciers that formed on Antarctica 30 million years ago, when its climate resembled Alberta's or Patagonia's. Most of East Ant- arctica's bedrock sits 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 bed- rock is far different, with parts that are far deeper. This area was once the ocean bottom, a region where the continent was stretched and broken into smaller blocks with deep seabed between. Large islands made of volcanic mountain ranges are linked together by the thick blanket of ice. But the ice here is warmer, and moving faster. 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 tem- peratures like those of a few mil- lion years ago. The realization that the West Antarctic ice sheet was gone in the past is the cause of great con- cern in the global warming era. Early stages of a large-scale re- treat 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. The height of the sur- face has been dropping by up to 3 feet each year. Huge cracks have formed at the coast, and many large icebergs have been set adrift. The glacier is flowing at over a mile per year, and this speed has nearly doubled in the past three decades. Two decades of satellite data show the fastest ice loss in the vicinity of the Thwaites Glacier. NASA. This area was noted early on as a place where the ice could lose its grip on the bedrock. The re- gion was termed the "weak un- derbelly" of the ice sheet. Some of the first measure- ments of the ice depth, using ra- dio echo-sounding, showed that the centre of West Antarctica had bedrock up to a mile and a half below sea level. The coast- al area was shallower, with a few mountains and some higher ground; but a wide gap between the mountains lay near the coast. Ted Scambos, is Senior Research Scientist, CIRES, University of Colorado Boulder Broken ice where Thwaites Glacier heads out to sea (Photo: Ted Scambos)