Greenland’s rate of glacier retreat has doubled over last 20 years: study

By Stephen Beech via SWNS

Greenland’s rate of glacier retreat has doubled over the last 20 years, reveals a new report.

The latest study comes just days after different research showed a third of Greenland's ice sheet had melted away in the last 45 years.

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.

Their findings, published in the journal Nature Climate Change, show that glacier retreat has accelerated dramatically in the 21st Century.

To piece together the magnitude of glacier retreat, researchers from Northwestern University in the US and Denmark's University of Copenhagen combined satellite images with historical aerial photographs of Greenland’s coastline.

The coast is dotted with thousands of glaciers that are separate from the island’s massive central ice sheet.

The researchers were able to document changes in the lengths of more than 1,000 glaciers over the past 130 years.

Their findings show that although glaciers in Greenland have experienced retreat throughout the last century, the rate of their retreat has accelerated rapidly over the last two decades.

The team calculated that the rate of glacial retreat during the 21st Century is twice as fast as retreat during the 20th Century.

And, despite the range of climates and topographical characteristics across Greenland, the findings are ubiquitous, even among Earth’s northernmost glaciers.

First author Dr. Laura Larocca said: “Our study places the recent retreat of peripheral glaciers across Greenland’s diverse climate zones into a century-long perspective and suggests that their rate of retreat in the 21st Century is largely unprecedented on a century timescale.

“The only major possible exception are glaciers in northeast Greenland, where it looks like recent increases in snowfall might be slowing retreat.”

The study finds that climate change explains the accelerated glacier retreat - and that glaciers across Greenland respond quickly to changing temperatures.

Dr. Larocca said: “Our activities over the next couple of decades will greatly affect these glaciers.

"Every bit of temperature increase really matters.”

Senior author Professor Yarrow Axford [CORRECT], of Northwestern University, said: “This work is based on vast analyses of satellite imagery and digitization of thousands of historical aerial photographs - some taken during early mapping expeditions of Greenland from open-cockpit airplanes.

“Those old photos extend the dataset back prior to the satellite era when widespread observations of the cryosphere are rare.

"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.”

Most previous climate change research concentrated on the Greenland Ice Sheet, which covers around 80 percent of the country.

But 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.

Before the launch of Earth-observing satellites in the 1970s, researchers did not have a full understanding of how temperature changes affected Greenland’s glaciers.

A breakthrough came around 15 years ago when long-forgotten aerial photographs of Greenland’s coastline were rediscovered in a castle outside Copenhagen.

Now housed within the Danish National Archives, the images enabled study senior author Dr. Anders Bjørk, of the University of Copenhagen, to begin constructing the glaciers’ history.

Dr. Larocca said: “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.

“They also unintentionally captured the state of Greenland’s peripheral glaciers.”

Dr. Bjørk and colleagues digitized and analyzed photos to study 361 glaciers around Greenland.

In the new study, Dr. Larocca, Prof Axford and their team added records for 821 more Greenland glaciers and extended Dr. Bjørk’s records to the present day.

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.

Dr. Larocca, who began the project in 2018, said: “There really aren’t any automated processes to digitize all these photos.

“A project like this takes a lot of people and a lot of manual labor to scan and digitize all these analog air photos.

"Then, we had to do a lot of preprocessing work before making our measurements.”

The 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 percent of their lengths, while glaciers in other regions lost between five and 10 percent of their lengths over the past 20 years.

Dr. Larocca said: “Peripheral glaciers only represent about four percent of Greenland’s total ice-covered area, but they contribute 14 percent of the island’s current ice loss - a disproportionately large portion."

She added: “If you look globally at all glaciers that are distinct from the Greenland and Antarctic Ice Sheet, they have contributed roughly 21 percent of observed sea level rise over the last two decades.

"So, these smaller ice masses are an important part of the sea level problem.

"Millions of people worldwide also rely on glaciers for fresh water, agriculture and hydropower, so it’s deeply concerning that we’re allowing this to continue.

"The choices we make over the next few years will make a huge difference to how much ice we lose.”