Earth-orbiting satellites are watching Antarctica thaw.
Eighty scientists from over 40 earth sciences agencies, including NASA and the European Space Agency, used satellite data from between 1992 to 2017 to find that Antarctica has lost three trillion tons of ice to the oceans over this 25-year period.
Their research, published Wednesday in the journal Nature, confirms a troubling trend, as much of the world's fresh water is frozen away in Antarctica. It's accelerating melt will likely play a primary role in swelling Earth's oceans two or three feet higher this century, or perhaps as much as six feet.
The most vulnerable masses of ice are in West Antartica, where NASA has already witnessed an accelerating melt.
"They're melting like gangbusters," Josh Willis, an oceanographer at NASA's Jet Propulsion Laboratory, said in an April interview.
"These are massive rivers of ice that are dumping just huge amounts of ice into the oceans."
Image: imbie/Planetary Visions
Perhaps most worrying, said Willis, is that this melting is unprecedented. Scientists are watching this thawing for the first time. They can see the melt is already accelerating — and it's unknown what's exactly to come.
"We have long suspected that changes in Earth’s climate will affect the polar ice sheets," Andrew Shepherd, a climate scientist and one of the study's lead authors, said in a statement.
"Thanks to the satellites our space agencies have launched, we can now track their ice losses and global sea level contribution with confidence," said Shepherd. "According to our analysis, there has been a steep increase in ice losses from Antarctica during the past decade, and the continent is causing sea levels to rise faster today than at any time in the past 25 years."
Over this 25-year period, scientists measured around 7 and a half millimeters of sea level rise from the ice-clad continent.
This might not seem like a lot, Robin Bell, a marine geologist at Columbia University's Lamont-Doherty Earth Observatory, said over email. But, the more recent rapid loses in Antarctic ice "indicates Antarctica can change faster than we thought," said Bell.
In fact, 40 percent of the total rise, or about 3 millimeters, came in the last 5 years. That's when things really started to change.
Until 2012, the study's researchers found that Antarctica had been shedding 84 billion tons of ice into the sea each year, incrementally boosting sea levels by around 0.2 millimeters annually.
But beginning in 2012, Antarctica began to lose nearly 240 billion tons per year, largely from two giant West Antarctic glaciers, Pine Island and Thwaites.
The West Antarctic ice is particularly vulnerable because these massive ice sheets sit over the ocean, and even slightly warmer ocean waters can eat away at them from the bottom.
"The largest mass loss is observed where relatively warm ocean waters are melting floating ice shelves from below," Steve Rintoul, a study coauthor and physical oceanographer from the Antarctic Climate and Ecosystems Cooperative Research Center, in Australia, said in a statement.
These masses of ice, which sit on the edge of the continent, act as a plug, holding the continent's thick sheets of heavy ice back.
"As the ice shelves thin and weaken, they provide less resistance to ice flow from the continent to the sea," explained Rintoul. "This increases the rate of mass loss from the Antarctic Ice Sheet and therefore the rate of sea level rise."
This leads to a foreboding future. Once these melting ice sheets on the coast go, nothing is left to hold West Antartica's ice back. And as the authors note, "The ice sheets of Antarctica hold enough water to raise global sea level by 58 meters."
Certainly, no one is suggesting this will all dump into ocean — not nearly. But only an insignificant amount needs to melt into the sea for coastal dwellers, where billions reside and many more are expected to live, to be impacted by rising seas, flooding, and surges of stormwater. Around 40 percent of Americans, for example, live directly on the shoreline.
To better grasp exactly how much ice is lost each year — and more critically, how fast these losses are accelerating — space agencies will continue to peer onto the thawing continent. And down on Earth, scientists will even depend on seals, fitted with data-collecting devices, to dive under this melting ice.