Individual Glacier Shapes Influence Ice Loss in Greenland, Researchers Find
April 17, 2017
Thinning glaciers in Greenland play a major role in rising sea levels around the globe. An international team of researchers, including a University of Idaho professor, have found that the glaciers’ shapes influence how quickly they thin and melt — allowing them to identify which glaciers are most likely to contribute to sea level rise.
Scientists at The University of Texas Institute for Geophysics led the NASA-funded study, which also included Tim Bartholomaus, an assistant professor of geography in the UI College of Science. Their paper was published in Nature Geoscience today.
The Greenland Ice Sheet is the second-largest ice sheet on Earth and has been losing mass for decades, a trend scientists have linked to a warming climate. However, the mass change experienced by individual coastal glaciers, which flow out from the ice sheet and into the ocean, is highly variable. This makes predicting the ice sheet’s impact on future sea-level rise difficult.
“We were looking for a way to explain why this variability exists, and we found a way to do that that has never been applied before on this scale,” said Denis Felikson, the study’s lead author and a doctoral student at the University of Texas (UT).
Bartholomaus, who worked with Felikson at UT before coming to UI in August 2016, developed the idea for the analysis with colleagues, and helped guide the research. Bartholomaus’ research expertise focuses on the factors that lead glaciers to speed up or slow down, lose mass or calve icebergs.
“I was thinking about the ways in which glaciers thicken or thin, and how their geometry could affect that,” Bartholomaus said. “I wondered if we could combine our knowledge of glacier thickness and steepness to predict the thinning patterns. That turned out to work pretty well.”
Bartholomaus emphasized that understanding glacier melt and resulting sea-level rise is important even for people in the Inland Northwest, far from the coast.
“We’re all in this together. Everybody who pays taxes should be concerned about people’s insured property being destroyed,” Bartholomaus said. “The other goal is there are millions of people who are going to be displaced around the globe by rising sea level. It’s a humanitarian issue.”
Of the 16 glaciers the researchers investigated in West Greenland, the study found four that are most susceptible to thinning. One, Jakobshavn Isbrae, is responsible for at least 81 percent of the total mass loss from West Greenland over the past 30 years. Other glaciers are hardly changing at all.
The analysis of these differences works by calculating the potential for thinning to propagate inland from the glacier’s terminus — the edge of the glacier exposed to ocean water. Glaciers with thinning that reaches farthest inland are the most susceptible to ice mass loss. The researchers confirmed the capability of their predictions by comparing them to observed glacier thinning, then used this idea to identify a set of glaciers’ thinning limits.
Just how susceptible a glacier is to thinning depends on its thickness and surface slope, features that are influenced by the landscape under the glacier. In general, thinning spreads more easily across thick and flat glaciers and is hindered by thin and steep portions of glaciers.
“The geometries of all the glaciers are different, so these thinning limits are at different places for different glaciers,” Felikson said. “If a thinning limit is very close to the front of a glacier, it won’t allow that glacier to lose as much ice mass as if the thinning limit is very far inland.”
The research revealed that most glaciers are susceptible to thinning between 10 and 30 miles inland. For Jakobshavn, however, the risk of thinning reaches over 150 miles inland — almost one-third of the way across the entire Greenland Ice Sheet.
While the method can point out vulnerable areas, it can’t predict how much mass loss is likely to occur. Still, knowing which glaciers are the most at risk can help scientists allocate limited resources.
“The approach we demonstrate here allows us to identify which outlet glaciers are not yet changing rapidly, but might,” Bartholomaus said. “With that knowledge, we can anticipate potential sea-level rise and set up the observational campaigns in advance to understand these glacier changes.”
This new knowledge of glacier melt also will help scientists refine the models used to predict sea-level rise.
“This work and my work in general is focused on better understanding how glaciers and ice sheets work – i.e., their physics,” Bartholomaus said. “Then we can build that understanding into computer simulations and make better projections of glacier and ice sheet change.”
Other collaborators on the study include researchers at Iceland’s Institute of Earth Sciences, the University of Copenhagen, the University of California, the University of Kansas, Oregon State University and the University of Oregon. The research was funded by NASA through grant number NNX12AP50G and by funding from the University of Texas Aerospace Engineering and Engineering Mechanics Department.
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