Greenland glacial melt is growing factor in rising sea levels

Greenland’s glaciers are far more vulnerable to climate-change-induced warming oceans than previously thought, according to a report released Sunday by the University of California at Irvine and NASA glaciologists.

The study, published in the journal Nature Geoscience, reveals previously uncharted deep valleys stretching for dozens of miles under the Greenland ice sheet, showing that there are no natural barriers to stop the melting.

The findings echo a report released last week showing that glacial melting in West Antarctica is now “unstoppable” because of topographical conditions that, similarly, will not slow the glaciers’ retreat.

Bedrock canyons in Greenland sit well below sea level, which means that warming ocean waters will erode the ice much more than previously assumed. This could mean the melting will have a much more significant effect on global sea level rise.

“We know that many glaciers in Greenland are accelerating and retreating and that these changes are triggered by warming ocean currents,” said Mathieu Morlighem, a U.C.-Irvine associate project scientist who is a lead author of the Greenland study. The glaciers are melting faster because of warming ocean temperatures as well as the lack of topographical barriers to stop the process.

“Older models predicted that the glaciers would retreat until they reach higher ground and stabilize,” he said. “The amount of sea level [rise] from Greenland was therefore predicted to be limited.”

Morlinghem called previous rise estimates “too conservative.”

The two reports “suggest that the globe’s ice sheets will contribute far more to sea level rise than current projections show,” said co-author Eric Rignot of U.C.-Irvine and NASA’s Jet Propulsion Laboratory.

The Intergovernmental Panel on Climate Change in August warned of a three-foot sea level rise by 2100. But with new insight into melting glaciers in West Antarctica, that increase must be revised to at least seven feet.

Greenland's exact contribution to sea level rise incorporating this new information is unknown at this point. Older models predicted that once melting glaciers reached higher ground in a few years, the ocean-induced melting would be stopped.

“This turns out to be incorrect,” Morlighem said. “This has major implications because the glacier melt will contribute much more to rising seas around the globe.”

“But it is impossible to say whether the retreat is unstoppable or not at this point,” he added.

The Greenland study was based on a groundbreaking method that for the first time revealed the ground level of the subcontinent, which is as much as three miles below the ice cap’s surface in some places.

The models showed that what appeared to be shallow glaciers on the coasts of Greenland are actually deep ones in valleys that reach almost 65 miles inland.