On April 8, 2011, NASA’s Operation IceBridge flew a mission to coastal areas in southwest Greenland. Mountains and an open-water fjord surround one of the mission’s targets, a small ice cap called Sukkertoppen Isflade. Credit: Michael Studinger/NASA

Greenland’s glaciers are more vulnerable to melting by warm ocean waters than previously thought, a new study of the topography of the bedrock under the ice finds. This clearer picture of the underpinnings of the miles-thick ice sheet, along with other recent studies that suggest parts of Earth’s polar regions are not as stable as once thought, could mean that current projections of future sea level rise are too low.

On April 8, 2011, NASA’s Operation IceBridge flew a mission to coastal areas in southwest Greenland. Mountains and an open-water fjord surround one of the mission’s targets, a small ice cap called Sukkertoppen Isflade.

The new Greenland findings, detailed online May 18 in the journal Nature Geoscience, come on the heels of an announcement by the same group of researchers at the University of California, Irvine, that some of the largest and fastest-moving glaciers of the West Antarctic Ice Sheet have entered a phase of “unstoppable” collapse. The mechanisms driving the melt are different for the two ice sheets, though.

Unlike the Antarctic glaciers, which end in tongues of ice that float on the Southern Ocean seas, the glaciers of Greenland terminate with the land, butting up against the surrounding water. So instead of warm water melting the glaciers from below, as in Antarctica, the ocean waters melt the vertical fronts of Greenland’s glaciers. Scientists had thought that the melt of the Greenland glaciers would continue for a few decades, until the ice melted back to a point where the ground was higher than sea level and then would halt.

But the new study, which resulted in the most detailed topographic map of the periphery of Greenland to date, found that wasn’t the case: Valleys underlying many of the glaciers stay below sea level and extend much farther inland than previously suggested, so warm ocean currents that have migrated northward with the changing climate could eat away at the ice for much longer than current climate models suggest. “It will take much longer for these glaciers to lose contact with the ocean,” study author Mathieu Morlighem, of the University of California, Irvine, told Climate Central.

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