An aerial view of the Greenland ice sheet taken in 1992. Image: Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research

It’s well known that Greenland contains a ton of frozen water—enough to raise sea levels by nearly 25 feet were it all to melt. Unfortunately, new research suggests melting may occur faster than we thought as the Earth warms, because of how Greenland’s glaciers are anchored to bedrock.

A study published this week in Geophysical Research Letters finds that we’ve been underestimating how many of Greenland’s coastal glaciers are at risk of increased melting due to climate change—by a factor of two to four. Scientists at UC Irvine, NASA’s Jet Propulsion Laboratory, and elsewhere reached that conclusion by constructing the highest resolution maps to date of Greenland’s coastal seafloor and bedrock.

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These maps reveal that many coastal glaciers are deeply rooted, making contact with bedrock more than 200 feet below sea level. Somewhat counterintuitively, deep-rooted glaciers are exposed to warmer water—3 to 4 degrees Celsius (6 to 8 degrees Fahrenheit) warmer than the waters chilling near Greenland’s surface, which hail from cooler Arctic sources.

“We know that the retreat and acceleration of many glaciers around Greenland is triggered by the interactions between the ice and this warm water,” lead author Mathieu Morlighem, an Earth scientist at UC Irvine, told Earther. “Our new mapping shows that many of the fjords where the glaciers are currently flowing are deep and extend over long distances with no obstacles that may block this warm water as they retreat.”

In order for these deep-rooted glaciers to lose contact with that warm water, Morlighem says, they have to retreat very far inland. This process will take a long time, suggesting that as ocean temperatures rise, Greenland will continue to lose mass for centuries to come.

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Maps of Greenland’s coastal seafloor and bedrock created for the new study. Image: AGU/GRL/UC Irvine

“In the past, since we did not know how deep the bed was near the coast, it had been suggested that the melting of the Greenland ice sheet would not last very long, as the glaciers would not need to retreat far inland to lose contact with these warm ocean currents,” Morlighem explained. “We have shown here that this is obviously not true.”

The analysis drew on data from NASA’s Ocean Melting Greenland (OMG) campaign, which includes aerial surveys of the ice sheet’s perimeter that measure changes in ice sheet height, ocean temperatures and salinity around more than 200 fjords where glaciers meet the sea. It also drew on data from NASA’s Operation IceBridge, another airborne survey that measures ice sheet depth.

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“This is a strong, solid, useful study,” Richard Alley, a glaciologist at Penn State University who was not involved with the work, told Earther. “Many past models have not fully resolved the deep outlets where [ice] flow is especially fast. With this improved map, the focus can shift to improving the modeling.... to more accurately project the future of the ice sheet and thus of sea level.”

As glaciologists continue refining their models of Greenland’s future—and the future of coastlines around the world—climate change has already arrived to the vast icy island. Temperatures in the Arctic are rising at about twice the global average rate. A study published last year found that Greenland lost a whopping one trillion tons of ice between 2011 and 2014.

Crucial ice flows, like the Petermann Glacier in northwest Greenland, are changing before our eyes, cracking up and spitting hefty chunks of ice into the sea. But if the new study is any indicator, the changes we’re witnessing now are quite literally the tip of the iceberg.

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