This is an incredibly important article. Dramatic worldwide sea level rise is not something that might occur in 100 or more years, but rather what we may experience within a decade. We cannot say that we haven’t been warned about the human caused climate emergency again and again, and not just for years, but for decades. We cannot say that we did not know that there is a planetary crisis that has long demanded our individual and collective action to effect radical systemic change. There is no time left to turn away, stay silent, and abdicate our deep responsibility to act and stand in fierce protection of our children and grandchildren and all of the children of all of the species on our endangered planet Earth. — Molly
By Douglas Fox
On December 26, 2019, Erin Pettit trudged across a plain of glaring snow and ice, dragging an ice-penetrating radar unit the size of a large suitcase on a red plastic sled behind her. The brittle snow crunched like cornflakes underneath her boots—evidence that it had recently melted and refrozen following a series of warm summer days. Pettit was surveying a part of Antarctica where, until several days before, no other human had ever stepped. A row of red and green nylon flags, flapping in the wind on bamboo poles, extended into the distance, marking a safe route free of hidden, deadly crevasses. The Thwaites Ice Shelf appeared healthy on the surface. But if that were the case, Pettit wouldn’t have been there.
Pettit was studying defects within the ice, akin to hidden cracks in an enormous dam, that will determine when the ice shelf might crumble. When it does, the rest of the West Antarctic Ice Sheet behind it could flow right into the ocean, pushing up sea levels around the planet, flooding coastal cities worldwide.
From a distance, the ice shelf looks flat, but as Pettit walked she saw the guide flags ahead of her rise and fall against the horizon—a sign that she was walking across an undulating surface. To Pettit, a glaciologist at Oregon State University in Corvallis, this was significant. It meant that the ice’s underside was a rolling landscape—not what anyone expected. In satellite images, the center of the ice shelf looks stable. But it isn’t, Pettit says: “There are five or six different ways this thing could fall apart.”
The Thwaites Ice Shelf begins where the massive Thwaites Glacier meets the West Antarctic coast. The shelf is a floating slab of ice, several hundred meters thick, extending roughly 50 kilometers into the Southern Ocean, covering between 800 and 1,000 square kilometers. For the past 20 years, as the planet has warmed, scientists using satellites and aerial surveys have been watching the Thwaites Ice Shelf deteriorate. The decline has caused widespread alarm because experts have long viewed the Thwaites Glacier as the most vulnerable part of the larger West Antarctic Ice Sheet. The ice shelf acts as a dam, slowing its parent glacier’s flow into the ocean. If the shelf were to fall apart, the glacier’s slide into the sea would greatly accelerate. The Thwaites Glacier itself holds enough ice to raise the global sea level by 65 centimeters (about two feet). The loss of the Thwaites Glacier would in turn destabilize much of the rest of the West Antarctic Ice Sheet, with enough ice to raise sea levels by 3.2 meters—more than 10 feet.
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Credit: Mapping Specialists
Since 1992 the glacier has hemorrhaged a trillion tons of ice. It is currently losing an additional 75 billion tons of ice every year, and the rate is increasing. What happens next, however, depends on processes that can’t be studied from the air—flaws within the shelf that could break it apart, accelerating the glacier’s demise. That’s why, in 2018, the British National Environmental Research Council and the U.S. National Science Foundation launched a $50-million effort called the International Thwaites Glacier Collaboration to study the glacier and its ice shelf up close.
The collaboration involved eight research teams, including one that reported this September that the glacier was retreating faster than had been predicted just a few years ago. Two of the teams visited the Thwaites Eastern Ice Shelf between November 2019 and January 2020. Pettit’s team examined the central part of the shelf, looking at structural defects and ocean currents underneath. I accompanied her team as an embedded journalist, earning my keep with unskilled labor, much of it involving a snow shovel. Another team investigated the back edge of the ice shelf along the continent’s submerged shore, sending a remotely operated submarine down a narrow hole to explore a crucial environment hidden under 600 meters of ice, where the shelf is melting most quickly. The results paint a worrisome picture. The ice shelf “is potentially going to go a lot faster than we expected,” Pettit says.
Antarctica’s ice sheet has consistently surprised those who study it. In February 1958 researchers in West Antarctica, 700 kilometers inland from the coastline, drilled four meters into the snow, lowered in 450 grams of explosives and detonated it with a muffled fuff that sprayed snow in the air. Geophones sitting facedown on the ice recorded the sound waves that reflected off the hard ground far below. By measuring the return time, Charles Bentley, then a graduate student at Columbia University, made a shocking discovery: the ice in this location was more than 4,000 meters thick—several times thicker than anyone expected— and rested on an old ocean floor 2,500 meters below sea level.
By the 1970s researchers were flying ice-penetrating radar in airplanes that crisscrossed the region. The scattered surveys confirmed that the West Antarctic Ice Sheet sits in a broad basin, deepest toward the center, with large glaciers spilling into the sea through gaps in the basin’s outer rim. Even as scientists testified to Congress in the late 1970s about carbon dioxide and the dangers of global warming, most of them didn’t think that Antarctica would lose its ice anytime soon. But in 1978 John Mercer, a glaciologist at the Ohio State University, sounded the alarm that West Antarctica represented “a threat of disaster.” If the ice sheet lost the shelves separating it from the sea, it might crumble far more quickly than people imagined. Three years later Terry Hughes, a glaciologist at the University of Maine, called out two specific coastal glaciers—Thwaites and Pine Island—as “the weak underbelly” where the collapse of the ice sheet would most likely begin. A pair of papers published in 1998 and 2001 by Eric Rignot, a glaciologist at NASA’s Jet Propulsion Laboratory, showed that these two glaciers were indeed thinning, melting from beneath, allowing ocean water to intrude farther inland under the ice.
Additional aerial surveys since then have shown that the Thwaites Glacier is especially troubling. The ground underneath the glacier is a relentless slope that drops deeper as it moves inland from the outer, seaward edge, allowing warm ocean water to slide under the glacier, melting it from below. As the ice thins, losing weight, it is also expected to lift off the bed and float on the intruding warm, dense water, allowing the water to penetrate even farther—eventually reaching the 2,500-meter trench at the heart of the continent. If that happens, “you’re going to unload the West Antarctic Ice Sheet,” says Ted Scambos, a glaciologist at the University of Colorado Boulder, who traveled with Pettit’s team in 2019–2020.
The glacier flows into the sea in two arms that move at different speeds. The “fast arm” on its western side is a fragile, floating “ice tongue.” In satellite images it resembles a shattered windshield, composed of hundreds of icebergs a kilometer or two across drifting into the ocean. The “slow arm,” on the glacier’s eastern side, is a smaller ice shelf that for years seemed more stable. The front edge butts into a submarine mountain ridge 40 kilometers off the coast. This ridge acts like a doorstop, creating back pressure that holds the ice shelf together.
Pettit and her team chose the mountain-buttressed eastern shelf for their expedition. In satellite images, the shelf’s central region appeared relatively stable, its surface smooth enough for small ski-mounted planes to land. A pair of mountaineers could scout for hidden crevasses and establish safe routes, allowing the team to move around freely. Pettit worried that visiting an apparently undamaged part of the ice shelf might limit their opportunity to learn something new. She didn’t need to worry.
The Western Ice Tongue of Thwaites has splintered into hundreds of icebergs, which look like raised plateaus, interspersed with sea ice perhaps a meter thick, all covered in snow. Credit: Douglas Fox
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