May 30, 2012
80-Year-Old Photos Aid In Greenland Ice Melt Study
Researchers from Denmark´s University of Copenhagen have gained new insight into the loss of ice mass in Greenland´s glaciers thanks to a chance discovery of 80-year-old photo plates discovered in a Danish basement.
It is often difficult for scientists to assess the scale and speed of Arctic ice melt, but the extremely rare photos provide them with a more accurate picture.
Greenland´s ice was rapidly melting in the 1930s, followed by a cooling period in middle of the 20th century, slowing the progression of ice melt. Then, the glaciers started melting again, picking up speed in the 2000s.
Lead author, Anders Anker Bjork, a doctoral fellow at the Natural History Museum of Denmark, had been trying to compile all imagery pertaining to Greenland´s glaciers. Through his searches in the archives of The Arctic Institute in Copenhagen in 2011 he had found flight journals for some old planes with references to the National Survey and Cadastre of Denmark, which in turn contacted him about a discovery of their own.
“They were cleaning up in the basement and had found some old glass plates with glaciers on them,” said Bjork. “The reason the plates were forgotten was that they were recorded for mapping, and once the map was produced they didn´t have much value.”
The National Survey and Cadastre of Denmark had been storing the photo plates since explorer Knud Rasmussen´s expedition to Greenland´s southern coast in the 30s. The images contained aerial photographs of land, sea and glaciers in the southeast region of the country, along with travel photos of Rasmussen´s team.
Bjork and colleagues digitized the 80-year-old images along with other aerial photographs and satellite images taken over the past 70 years and used software to look for differences in the shape of the southeast Greenland coastline where the ice meets the Atlantic Ocean. They then calculated the distance the ice front moved in each time period.
Analyzing the images, the researchers found two events that stood out most over the past 80 years: glacial retreats in 1933-34 and from 2000 to 2010. In the 30s, fewer glaciers were melting than are today, and most of those that were melting were land-terminating glaciers, meaning they had no contact with the sea.
But those that were melting were retreating at the average rate of 65 feet per year and up to 1,225 feet per year. More than 50 percent of the glaciers in the study had similar or higher retreat rates in the 30s than they do today.
While melting rates are not occurring as fast as they were in the 30s, more glaciers are retreating today. And, while the average ice loss is around 150 feet per year, that is because a few glaciers have very fast melting rates, driving the average up.
And despite the ongoing ice loss, our results “show that glaciers can recuperate within a short time frame if climate changes and temperatures drop, as it has in a period after the 1940s,” noted Bjork.
“Most of the scientific foundation, models, and theories on glaciers in Greenland and how global warming affects them are based on observations from satellites over the last ten years. Otherwise scientists have had to use previous warming events way into the past when wanting to compare today´s massive retreat,” he added.
Southeast Greenland is a good place to study the effects of climate change, explained Jason Box, associate professor of geography and researcher at the Byrd Polar Research Center at Ohio State, because the region is closely tied to air and water circulation patterns in the North Atlantic.
“By far, more storms pass through this region - transporting heat into the Arctic - than anywhere else in the Northern Hemisphere. Climate change brings changes in snowfall and air temperature that compete for influence on a glacier´s net behavior,” he said.
Publishing their work in the journal Nature Geoscience, the Danish team has garnered international attention with their work, as Greenland stands as an important region that affects the planet´s climate, as well as changes in glacial conditions and related sea-level rise.
“We have investigated no less than 132 glaciers on a 600 km (375 mile) coastal stretch in Southeast Greenland, both those who terminate on land and those who calve in the ocean. The historical photos have proven to be extremely valuable, and with these photos and other aerial photos recorded later during WWII and satellite imagery we are able to observe glacier change in very long historical context,” said study coauthor Dr. Kurt H Kjar. “In the early 1920s and 1930s, temperatures were high, similar to that of the present, and this affected the glacial melt. At the time many glaciers underwent a melt similar or even higher than what we have seen in the last ten years. When it became colder again in the 1950s and 1960s, glaciers actually started growing,”
“There should be no doubt that if the current temperature rise in Greenland continues then we will have problems with the melting of the glaciers. We are already seeing it now on the marine terminating glaciers where changes in temperature and ocean currents are influencing their stability. Another remarkable discovery we did was that the observed changes are not just local, it is happening in the entire region,” said Kjar.