By MANDA MORRIS and TOM DINKI
Published November 14, 2023
Greenland’s thousands of peripheral glaciers have entered a new and widespread state of rapid retreat, a study involving UB researchers has found.
Combining satellite images with historical aerial photographs of Greenland’s coastline, a research team led by Northwestern University and the University of Copenhagen determined that the rate of glacial retreat during the 21st century is twice as fast as retreat during the 20th century.
“The results add to growing documentation that glaciers in the Arctic are responding quickly to rising temperature due to human-caused climate change. This is concerning because their meltwater contributes to global sea level rise,” says Jason Briner, professor of geology, College of Arts and Sciences, and co-author on the study, which was published Nov. 9 in the journal Nature Climate Change.
Prior to the launch of Earth-observing satellites in the 1970s, researchers did not have a full understanding of how temperature changes affected Greenland’s glaciers. Widespread and detailed observational records simply did not exist — or so researchers thought.
A breakthrough came about 15 years ago when long-forgotten aerial photographs of Greenland’s coastline were rediscovered in a castle outside Copenhagen.
“Starting in the 1930s, Danish pilots clad in polar bear-fur suits set out on aerial mapping campaigns of Greenland and ended up collecting over 200,000 photos of the island’s coastline,” says the study’s first author, Laura Larocca, a National Oceanic and Atmospheric Administration Climate & Global Change Postdoctoral Fellow who was a PhD candidate at Northwestern University when the research began in 2018. “They also unintentionally captured the state of Greenland’s peripheral glaciers.”
The images enabled Anders Bjørk, the study’s senior author and assistant professor at the University of Copenhagen, to begin constructing the glaciers’ history.
In previous studies, Bjørk and his collaborators digitized and analyzed photos to study 361 glaciers in the southeast, northwest and northeast regions of Greenland. In the new study, the team led by Northwestern added records for 821 more glaciers in the south, north and west regions, and extended Bjørk’s records to present day.
As a part of this effort, the team digitized thousands of paper-copy aerial photographs taken from open-cockpit planes and collected imagery from multiple satellites. The researchers also removed terrain distortion and used geo-referencing techniques to place the photos at the correct locations on Earth.
The team extended records further back in time by leveraging clues hidden within the landscape. When glaciers grow larger and then retreat, they leave behind a terminal moraine — sediment transported and deposited by a glacier, often in the form of a long ridge. Locating these moraines enabled the researchers to map older glacier extents before pilots took their first flyover photos in the early 1930s.
Altogether, this one-of-a-kind data documents changes in the lengths of more than 1,000 of the country’s glaciers from 1890 to 2022.
“It’s quite extraordinary that we can now provide long-term records for hundreds of glaciers, finally giving us an opportunity to document Greenland-wide glacier response to climate change over more than a century,” says senior author Yarrow Axford, William Deering Professor of Geological Sciences in Northwestern’s Weinberg College of Arts and Sciences
Using the late 20th-century imagery as a baseline, the team calculated the percentage of length that glaciers have lost over the past 20 years. They found that, on average, glaciers in south Greenland lost 18% of their lengths, while glaciers in other regions lost between 5-10% of their lengths over the past 20 years. The only major possible exception are glaciers in northeast Greenland, where recent increases in snowfall might be slowing retreat.
Peripheral glaciers represent only 4% of Greenland’s total ice-covered area but contribute 14% of the island’s current ice loss.
“These glaciers, given their comparably smaller size, are the real canaries in the coal mine — they respond very quickly to Arctic warming,” Briner says. “Most projections of future sea level rise demonstrate that humanity still controls the knob. Fast action can stabilize temperature and sea level change after some in-the-pipeline change plays out.”
Avriel Schweinsberg, who received her PhD from UB in 2018, is also a co-author on the study.
The study was supported by the National Science Foundation’s (NSF) Geography and Spatial Sciences Program, NSF Polar Programs, the University Corporation for Atmospheric Research’s Cooperative Programs for the Advancement of Earth System Science and the Villum Foundation.