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Pay attention to Greenland.

The Watch Honest Thief Onlineland's colossal ice sheet — around three times the size of Texas — is melting some 270 billion tonsof ice into the sea each yearas Earth warms. And the inevitable sea level rise could be worse than scientists calculated: Researchers at NASA and the University of California, Irvine (UCI) found that warmer ocean water is seeping underneath and amplifying melting of Greenland's mighty Petermann Glacier, which ends in a great ice tongue floating over the sea. The scientists recently published their research in the journal Proceedings of the National Academy of Sciences.

The glacier lies in northern Greenland, a realm of the high Arctic. But that frigid location can no longer protect it. Scientists found the glacier is vulnerable to the incessantly warming seas. It's another whammy for melting Greenland, which is melting from above (warmer air) and below (warmer water).

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Until 2015, satellite observations showed Petermann, a major ice outflow on Greenland, was in solid shape. Not anymore.

"Something changed during the last decade. Petermann was supposed to be a place where the ice was still stable," Enrico Ciraci, a NASA postdoctoral fellow and an Earth system scientist at UCI, told Mashable.

SEE ALSO: Why the U.S. will get a whole lotta sea level rise

Ice loss is now ramping up.

"Warming oceans are accelerating the mass loss of this glacier,"Ciraci, who led the research, said.

"Warming oceans are accelerating the mass loss of this glacier."

Not even the coldest glaciers are immune.

"It's surprising even Petermann isn't escaping the impacts of global warming," Josh Willis, a NASA oceanographer who researches melting in Greenland and had no involvement with the new research, told Mashable.

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A graph showing continual ice mass loss on Greenland. Credit: NASA

How Greenland's melting boosts sea level rise

For some of us, sea level rise might not be nearly as apparent or poignant as the increase in inferno-like Western wildfires, record-breaking heat waves, vanishing Arctic ice, and historic deluges. But it's happening, and it's speeding up.

Since the late 19th century, global sea levels have already risen by some eight to nine inches. Sea level rise each year more than doubled from 1.4 millimeters over most of the 20th century, to 3.6 millimeters by the early 21st century. From just the years 2013 to 2018, that number accelerated to 4.8 millimeters per year.

Yet, crucially, most sea level rise simulations and predictions don't take into account what's happening under Petermann and the many glaciers like it. This means we might be underestimating sea level rise over the coming decades and beyond. In the study, the researchers noted that such ocean melting "will make projections of sea level rise from glaciers potentially double."

"This process is not accounted for in many models today for sea level rise," Ciraci explained. "The potential contribution is significant."

The process involves glaciers, which are common on Antarctica, that end in sheets of ice (called "ice shelves") that float over the ocean. The ice shelves are hugely important. There's a point, called a grounding line, where the ice meets the ocean floor, while the rest of the shelf extends over the ocean. This grounding area acts like a cork in a bottle, keeping the glacier from flowing unimpeded into the sea. But, using bounties of detailed radar satellite observations, Ciraci and his team found that Petermann's grounding zone continually moved back and forth with the ocean tides by miles. During this time, warm waters seeped into channels in the ice shelf, eating away at the ice.

Here are some powerful numbers: Since 2016, warm water seepage melted away a 670-foot-tall cavity in the glacier. Overall, the pivotal grounding zone moved back by 2.5 miles.

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Ice breaking off of Petermann Glacier, at center. It's normal for icebergs to calve off glaciers, but Petermann is now retreating back as more ice melts than is naturally replenished. Credit: NASA The ocean's global heat content has been relentlessly rising for over three decades. Credit: NOAA

Ultimately, the glacier's highest rates of melting occurred in its susceptible grounding zone. This might portend significantly more melting to come from Petermann, but exactly how much is still uncertain.

"This could indicate easier destabilizing of the glacier in the future,"Ciraci said.

It's not surprising the ocean is eroding a giant glacier like Petermann. The ocean is the true keeper of climate change. It absorbs over 90 percent of the heat humans trap on Earth. It's continually warming. Already, NASA researchers — by flying over Greenland glaciers, dropping monitors into the water, and scrutinizing changes with satellites — have found ever-warming ocean water is eating away at the ends of Greenland's glaciers, hastening their melting as great chunks of ice calve into the sea.

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Now, there's proof the ocean is seeping in from below, like water seeping into your shoe after stepping into a puddle.

"It's eating away at the bottom of the ice, way more than we thought," NASA's Willis said. "Again, it's the ocean's fault."

This story was originally published on May 13, 2023 and has been updated with more information.