Researchers including the University at Buffalo have found that Greenland's outer glaciers are retreating at an alarming rate, with the rate of retreat in the 21st century being twice that of the 20th century. The discovery, from satellite and historical aerial data, highlights the rapid response of glaciers to climate change and the attendant risks of rising sea levels.
Greenland's outer glaciers are retreating rapidly, and recent research suggests that the rate of retreat will accelerate significantly in the 21st century. This highlights the urgent need to address climate change to mitigate its impact on sea levels.
Thousands of Greenland's outer glaciers have entered a new, widespread state of rapid retreat, University at Buffalo (UB) researchers have found in a study.
Combining satellite imagery with historical aerial photos of Greenland's coastline, a team led by Northwestern University and the University of Copenhagen determined that glaciers are retreating at twice the rate in the 21st century compared to the 20th century.
"These results add to a growing body of literature showing that Arctic glaciers are responding rapidly to rising temperatures due to human-caused climate change. This is concerning because their meltwater contributes to global sea level rise," said Jason Briner, a professor of geology in the College of Arts and Sciences and a co-author of the study, which was recently published in the journal Nature Climate Change.
Historical aerial photos: Key to understanding glacier history
Before the launch of Earth-observing satellites in the 1970s, researchers didn't fully understand the effects of temperature changes on Greenland's glaciers. Extensive and detailed observational records simply don't exist - or so researchers think.
The breakthrough came about 15 years ago when long-forgotten aerial photos of the Greenland coastline were rediscovered in a castle outside Copenhagen.
"Beginning in the 1930s, Danish pilots wearing polar bear fur suits began aerial mapping of Greenland, ultimately collecting more than 200,000 photos of Greenland's coastline," said Laura Larocca, lead author of the study. Larocca is a postdoctoral fellow in climate and global change at the National Oceanic and Atmospheric Administration and a doctoral candidate at Northwestern University when the study began in 2018. "They also accidentally captured the state of Greenland's outer glaciers."
The images allowed Anders Bjørk, the study's senior author and an assistant professor at the University of Copenhagen, to begin constructing the glacier's history.
In previous research, Bjork and his collaborators digitized and analyzed photos and studied 361 glaciers in the southeast, northwest and northeast regions of Greenland. In the new study, a team led by Northwestern University added records from 821 glaciers in the southern, northern and western regions and extended Björk's record to the present day.
A comprehensive history of glaciers
As part of this work, the team digitized thousands of paper aerial photos taken from open-top aircraft and collected images from multiple satellites. The researchers also removed terrain distortion and used geo-referencing technology to place the photos in their correct locations on Earth.
The research team used clues hidden in the landscape to extend the recorded time further forward. When a glacier grows and then recedes, it leaves behind terminal moraines -- sediments transported and deposited by the glacier, often in the form of long ridges. Before pilots took the first photos over the glacier in the early 1930s, researchers had pinpointed the location of these moraines, allowing them to map the glacier's extent much earlier.
Altogether, these unique data record changes in the length of more than 1,000 glaciers across the country from 1890 to 2022.
"We now have long-term records available for hundreds of glaciers," said Yarrow Axford, the study's senior author and the William Deering Professor of Geological Sciences in Northwestern's Weinberg College of Arts and Sciences. "It's extraordinary to finally have the opportunity to document the response of glaciers across Greenland to climate change for more than a century."
Study results: Glacier length significantly reduced
Using images from the late 20th century as a baseline, the team calculated the percentage of length the glacier had lost over the past 20 years. They found that glaciers in southern Greenland had lost an average of 18% in length, while glaciers elsewhere had lost 5-10% in length over the past 20 years. The only possible exception are glaciers in northeast Greenland, where recent increases in snowfall may have slowed glacier retreat.
Peripheral glaciers account for only 4% of Greenland's total ice cover, but account for 14% of the island's current ice loss.
"With their smaller size, these glaciers are the real canaries in the coal mine -- they respond very quickly to Arctic warming," Bryner said. "Most projections of future sea level rise suggest humans still control the knob. Quick action could stabilize changes in temperature and sea level after some changes within the pipeline occur."
Reference "L.J. Larocca, M. Twining-Ward, Y. Axford, A.D. Schweinsberg, S.H. Larsen, A. Westergaard-Nielsen, G. Luetzenburg, J.P. Briner, K.K. Kjeldsen and A.A. Bjørk, November 9, 2023, Nature Climate Change.
DOI:10.1038/s41558-023-01855-6
Compiled source: ScitechDaily