Greenland glaciers face a triple threat from global warming

Rising temperatures are an even bigger threat to the Greenland ice sheet than what was previously realized. Scientists at UC Irvine and the NASA Jet Propulsion Laboratory have quantified how warming coastal waters are impacting individual glaciers across the island. 

As part of the Oceans Melting Greenland (OMG) mission, the researchers have surveyed 226 glaciers for the past five years. The study revealed that 74 glaciers situated in deep valleys accounted for nearly half of Greenland’s total ice loss between 1992 and 2017. 

The fjord-bound glaciers were found to be the most impacted by undercutting, which is when warm seawater at the bottom of the canyons melts the ice from below.

By contrast, the team found that 51 glaciers positioned in shallower fjords experienced less undercutting and contributed only about 15 percent of the total ice loss.

“I was surprised by how lopsided it was. The biggest and deepest glaciers are undercut much faster than the smaller glaciers in shallow fjords,” said study lead author Michael Wood. “In other words, the biggest glaciers are the most sensitive to the warming waters and those are the ones really driving Greenland’s ice loss.”

The experts pointed out that warm seawater is able to accumulate more in deep fjords compared to shallow ones.

Meanwhile, rising air temperatures heat the surfaces of glaciers, creating pools of meltwater that ultimately flow into the ocean. Glacier meltwater is lighter than seawater and floats up to the bottom of the glaciers, dragging with it a plume of warm water that causes undercutting. 

The researchers explained that while fjord depth is a fairly fixed variable, other factors such as ocean temperature and meltwater accumulation are greatly impacted by climate change. All three factors combine to cause accelerated deterioration of Greenland’s ice sheet, they said.

The findings suggest that climate models which fail to account for undercutting may substantially underestimate glacial ice loss. In addition, the results may explain why many of Greenland’s glaciers never recovered after an abrupt period of ocean warming between 1998 and 2007, despite a pause in ocean warming between 2008 and 2017.

“We have known for well over a decade that the warmer ocean plays a major role in the evolution of Greenland glaciers,” said OMG Deputy Principal Investigator Eric Rignot. “But for the first time, we have been able to quantify the undercutting effect and demonstrate its dominant impact on the glacier retreat over the past 20 years.”

“When the ocean speaks, the Greenland Ice Sheet listens,” said study co-author Josh Willis. “This gang of 74 glaciers in deep fjords is really feeling the influence of the ocean; it’s discoveries like these that will eventually help us predict how fast the ice will shrink. And that’s a critical tool for both this generation and the next.”

The study is published in the journal Science Advances.

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By Chrissy Sexton, Earth.com Staff Writer