Five of the last six years have seen the most rapid glacier retreat on record, the UN’s World Meteorological Organization weather, climate and water agency said Copyright AFP FAYEZ NURELDINE
A new study documents how Greenland’s peripheral glaciers have changed from 1890 to 2022. By using satellite images and a unique archive of historical aerial photos, researchers have compiled the most complete picture of Greenland’s outlying glaciers to date. This shows how glacier retreat has accelerated dramatically in the 21st century.
Greenland’s thousands of peripheral glaciers have entered a new and widespread state of rapid retreat. This is according to a Northwestern University and University of Copenhagen study.
To assess the impact, scientists combined satellite images with historical aerial photographs of Greenland’s coastline, which is dotted with thousands of glaciers that are separate from the island’s massive central ice sheet. With these oneofakind data, the researchers documented changes in the lengths of more than 1,000 of the country’s glaciers over the past 130 years.
Although glaciers in Greenland have experienced retreat throughout the last century, the rate of their retreat has rapidly accelerated over the last two decades. According to the multiyear collaborative effort between the United States and Denmark, the rate of glacial retreat during the 21st century is twice as fast as retreat during the 20th century.
Despite the range of climates and topographical characteristics across Greenland, the findings are ubiquitous, even among Earth’s northernmost glaciers.
Accelerating glacier retreat
The study finds that climate change explains the accelerated glacier retreat and that glaciers across Greenland respond quickly to changing temperatures. This highlights the importance of slowing global warming.
While climate change’s effects on Greenland are well studied, most researchers focus on the Greenland Ice Sheet, which covers roughly 80% of the country. Yet fluctuations in Greenland’s peripheral glaciers — the smaller ice masses distinct from the ice sheet that dot the country’s coastline — are widely undocumented, in part due to a lack of observational data.
Prior to the launch of Earthobserving 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 longforgotten aerial photographs of Greenland’s coastline were rediscovered in a castle outside Copenhagen. Now housed within the Danish National Archives, the images enabled the researchers to begin constructing the glaciers’ history.
As a part of this effort, the team digitized thousands of papercopy aerial photographs taken from opencockpit planes and collected imagery from multiple satellites. The researchers also removed terrain distortion and used georeferencing techniques to place the photos at the correct locations on Earth.
Power of digital images
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.
Using the late 20thcentury imagery as a baseline, Larocca, Axford and their team also 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 510% of their lengths over the past 20 years.
As global temperatures increase, it has become more imperative than ever to better understand how these melting glaciers will affect rising sea levels and reliable sources of fresh water.
The research appears in the journal Nature Climate Change, titled “Greenlandwide accelerated retreat of peripheral glaciers in the twentyfirst century.”
