Climate change is wreaking havoc in Earth’s remotest corners. At the Thwaites Glacier in Antarctica, scientists found a massive cavity—roughly two-thirds the area of Manhattan—that has been growing in the ice for decades.
The hole lurks beneath the surface of the Florida-size glacier and measures 1,000 feet from top to bottom, scientists said in a study published on Wednesday in Science Advances. The study was led by researchers from NASA’s Jet Propulsion Laboratory, the University of California Irvine, the German Aerospace Center, and France’s University Grenoble Alpes.
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The cavity was revealed by data from NASA’s Operation IceBridge and spaceborne radar projects that documented Thwaites’ behavior between 1992 and 2017.
Pietro Milillo, a radar scientist at NASA’s Jet Propulsion Laboratory and lead author on the study, called it a “disturbing discovery.”
“This hole is big enough to have contained 14 billion tons of ice,” Milillo told Motherboard in an email. “To compare these numbers on a human scale, 1 billion tons is the water consumption of the City of Los Angeles in one year.”
Antarctic researchers have known about Thwaites’ “weak underbelly” for decades. Even so, the authors suspect the cavity’s size and melt rate have been underestimated by previous models.
The glacier’s runoff is responsible for up to 10 percent of annual global sea level rise, according to estimates from the National Science Foundation. If Thwaites melted entirely, the world’s oceans could rise by nearly two feet.
Tracking ice loss is no simple feat. Antarctic glaciers are often too big and too isolated to accurately measure from the ground.
Instead, the team used a fleet of low Earth orbit satellites and planes equipped with ice-penetrating radar to monitor Thwaites over time. What this revealed was “different mechanisms of retreat,” Milillo said.
Where the cavity looms on the glacier’s western front, its grounding line—the point where Thwaites affixes to the continental shelf—has been detaching from the bedrock at a rate of 0.4 to 0.5 miles per year since 1992, according to the study.
The cycle is perpetuated as the hole grows; as more water and heat get trapped beneath the ice, the faster it melts. Most of the 14 billion tons of ice disappeared within the last three years, according to the study.
To the east, Thwaites’ grounding line recedes through small channels, “like fingers reaching beneath the glacier to melt it from below,” Milillo described. Here, the rate of retreat has quickened from 0.4 miles a year between 1992 and 2011 to 0.8 miles a year from 2011 to 2017. (However, Thwaites’ western region is still melting faster than its eastern one.)
Plenty of things are responsible for the retreat, such as topography, thinning ice, and melt brought on by masses of warm, salty ocean water. “Ice-ocean interactions are more complex than previously understood,” Milillo said.
American and British science agencies recently embarked on a five year expedition to Thwaites, in an effort to better understand its terrifying potential for sea level rise on a massive scale.
“How much, how fast? That’s our mantra,” Robert Larter, a scientist with the British Antarctic Survey, told BBC News on Wednesday. “These are the questions we’re asking about Thwaites.”
Thwaites connects to the West Antarctic ice sheet which has also lost ice at an unprecedented pace. Separate research suggests that large swaths have retreated to “the point of no return,” and the whole West Antarctic ice sheet could raise global sea levels by 10 feet.
In the near future, Mililo expects that a new generation of satellites “will be capable of providing more accurate and more frequent measurements over the entire Antarctica and Greenland.”
