June 1, 2023

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The speed of melting of this glacier in Greenland may indicate a worse rise in sea level

Scientists studying one of Greenland’s largest glaciers say it is melting much faster than expected in its most vulnerable region, a worrying sign that existing ocean glaciers could be contributing to sea level rise more quickly than currently expected.

Scientists fear that the phenomenon observed at Petermann Glacier could happen to other glaciers in both Greenland and Antarctica, which could lead to a faster and more dramatic rise in sea levels around the world – “potentially doubling” what is currently expected from Glaciers, according to The study was published Monday.

Using satellite measurements of its surface, the researchers found that Petermann was bouncing up and down, dramatically shifting the seafloor anchors in response to the tides. All this movement has carved out a large cavern at the base of the glacier and has allowed the warm water to expand steadily beneath it. As the glacier rises and migrates, the water can rush over a mile, thinning the ice by as much as 250 feet annually in some places.

“You have this constant flow of seawater that goes many kilometers under the glacier and melts the ice,” said Eric Regno, one of the study’s authors and a glaciologist at the University of California, Irvine and the Jet Propulsion Laboratory at Caltech. .

“We think this could change sea level projections to some extent,” he said. The study was published Monday in the Proceedings of the National Academy of Sciences.

Petermann Glacier is, in the context of climate change, the next big thing that might break greenhouse gas emissions. The vast glacier is about ten miles wide One of the many major outlets for ice to escape from the interior of Greenland into the ocean. In total, the huge icy region lined up behind Petermann It could, if it all melted, raise global sea levels by more than one foot.

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Petermann hasn’t changed as much as some of the other Greenland glaciers, likely in part because it’s farther north. But it has undergone important transformations.

Petermann lost two massive pieces of ice from the floating ice shelf in 2010 and 2012, causing the shelf to lose nearly a third of its area. She hasn’t recovered since.

The glacier also began to move backward, such as the central region of The grounding line – where it sits on the floor of a deep fjord – retreated more than two miles inland towards Greenland. This occurred in response to the warming of the waters in the fjord in front of the glacier. The warming is only up to a fraction of a degree, according to Renott, but the water is now just above zero degrees Celsius. But it is more than warm enough to melt ice, especially at the depths and pressures seen at the grounding line.

At the same time, ice has begun to flow outward more quickly, which means that Petermann has swung from a fairly steady state to losing a few billion tons of ice to the ocean each year. It’s not much compared to some of the other major glaciers in Antarctica or Greenland, but it might just be the beginning.

All of this most likely reflects changes in the grounding line, which is very difficult to monitor. But satellites can detect both changes in the height of the glacier’s surface, which can be used to infer what’s going on underneath, and how the glacier responds to tidal cycles.

That’s what Petermann’s new research picked up on — showing that tidal cycles have very large effects on glacier melt. Satellites showed that There is no real base “line” – rather, there is a vast area, more than a mile long, on which the glacier moves back and forth along the sea floor. This movement speeds up melt as it allows seawater to mix near and even beneath the glacier.

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The research also found that a large cavity — 650 feet high — has now been hollowed out in the center of the grounding line. Its area is about 8 square miles, and in this area, the ocean can enter and cause melting even without the help of tides moving and lifting the glacier.

All of this, according to the researchers, has a very big implication — we may need to adjust our current models to account for the rapid melting in the swaying ground lines of large glaciers. This, in turn, could cause projections of sea level rise from these two giants to “potentially double,” the study suggests.

“There are probably plenty of other glaciers in this position, with tidal flow,” Regno said. He thinks Petermann is, on the whole, a good counterpart to what might also be happening in Antarctica, where there is much more ice than there is in Greenland.

The research was conducted by scientists at three US institutions — the University of California, Irvine, JPL at Caltech, and the University of Houston — in collaboration with international colleagues at institutions in China, Finland, Germany, and Italy.

Several scholars It is not affiliated with the study Findings from The Post were impressed by the new measurements, but not entirely convinced of their effects.

“The reported rates of melt are very large, much greater than anything we suspected in this region,” said Helen Serusi, a glaciologist at Dartmouth College who uses models to study glaciers and sea level rise.

However, Sirusi said, the models researchers use to predict sea level rise — complex sets of equations that are used to predict how glaciers around the world will respond to warmer oceans and air — won’t change immediately based on the results of the current. Stady.

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“We are still many years away from properly implementing these operations in numerical models,” Serusi said. “It is important to understand that there are always long delays between the discovery of a new process and its inclusion in the numerical models as these processes must be fully understood from a physical point of view,” which requires further research.

In particular, the operation involved, said Serusi It is not generally included because the scale at which it operates is not fully understood. Until that happens, some models can show a lot of ice loss due to this, simply because they represent the process as playing over a very large area.

Andreas Moncho, a scientist at the University of Delaware who studies the Petermann Glacier, had some cautionary notes.

“I very much like the idea of ​​a ‘tidal pulse’ for the terrestrial region of a glacier, where the glacier flutters with warm water that creeps in during the incoming tide and lifts down as the cold water comes out during the outgoing tide,” Moncho said.

However, he noted, “Very high rates of melting are real, but they are estimated in very small areas.”

“My main takeaway is that the models need to be improved,” Moynchou concluded. “The study provides a sharper focus on the processes we need to study floating glaciers in Greenland or Antarctica, if we want to predict future sea level rise using models.”

Overall, the new study confirms once again that we really don’t know how quickly one of the biggest consequences of climate change will happen – sea level rise from the melting of the Greenland and Antarctic ice sheets. We’re still discovering new details – and new reasons to think it might be faster than expected.