The gigantic ethereally beautiful glaciers of the Norwegian archipelago of Svalbard, near the North Pole, bear the scars of climate change more than almost anywhere else on the planet.
Over the past three decades, Svalbard has warmed twice as fast as the rest of the Arctic region and seven times the global average. This is causing the islands’ glaciers to melt at an alarming rate, threatening polar bears and other wildlife, and contributing to rising sea levels around the world.
For a long time, however, predicting how quickly future warming might drive ice retreat has been guesswork. In Svalbard and elsewhere, most field measurements did not begin until the middle of the 20th century, and satellite observations even later.
Today, advances in computing are helping scientists bring old ice back to life in stunning detail. Using black-and-white photos taken on mapping expeditions nearly a century ago, they create three-dimensional digital models of how glaciers looked before modern record keeping and shed light on how which they have changed over a longer period.
One of the largest such reconstructions to date, published Wednesday in the journal Nature, points to a troubling conclusion: Svalbard glaciers could be thinning twice as fast this century as they did. have done over the last.
“Right now, our predictions of future glacier evolution are not very well based on all the data we already have about what’s happened over the past century,” said Emily C. Geyman, graduate student at the California Institute of Technology and lead author of the new study. A deeper historical record allows scientists to test how well their models of glacial change align with the past, Geyman said, before using them to peer into the future.
“It’s a unique opportunity to look a little further back in time,” said Ward JJ van Pelt, an associate professor at Uppsala University in Sweden who contributed to the new research.
The team’s reconstruction of the Svalbard glaciers in 1936 reveals, in vivid detail, how much some of the ice sheets shrank between that date and 2010. The average rate of loss was around 1.1 feet per year.
Across the planet’s frosty roof, rapid warming is disrupting lives and disrupting vast wilderness landscapes. In its latest annual Arctic assessment, the US National Oceanic and Atmospheric Administration found that declining sea ice and snow cover continued to transform the region last year. The collapse of glaciers has caused landslides and tsunamis. Thawing permafrost, or continuously frozen ground, has destabilized homes and infrastructure built above.
Svalbard sits on the edge of Arctic sea ice in winter, Dr van Pelt said. Sea ice reflects much of the sunlight that hits it, so when the ice disappears, more solar energy is absorbed by the ocean, warming the water. This is the main reason why Svalbard is warming up faster than the rest of the globe.
To piece together the islands’ past, Ms Geyman and her co-authors used a treasure trove of more than 5,500 aerial images taken by a Norwegian mapping project in 1936 and 1938. Icy conditions made flying difficult and equipment was simple : a Zeiss camera mounted on a reconnaissance aircraft.
Yet the images, which are owned and managed by the Norwegian Polar Institute, a government research group, powerfully capture the drama of the landscape. “I was enchanted by the photos,” Ms Geyman said.
To turn the faded negatives into three-dimensional digital models, Ms Geyman had to tell her computer how to interpret the images. This involved selecting points on different photos that show the same feature in the landscape – a crevasse, for example, or a channel carved into the ice by meltwater – so the software could correctly stitch the images.
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In total, she placed almost 70,000 such dots in the photos. It took the better part of two years. “I started having to wear those glasses, I think,” she said, pointing to her face, “because of squinting so much at the pixelated images on my screen.”
In some places, the fresh white snow in the photos made it too hard to make out the terrain, so she filled in the gaps with estimates.
Once they had digital reconstructions of more than 1,500 glaciers across Svalbard, Ms Geyman and her co-authors compared them to those made from more recent images to determine how much ice had melted. since the 1930s.
They then used these specifications to predict that the average elevation of Svalbard glaciers would decrease by 2.2 to 3 feet per year before 2100, depending on the increase in greenhouse gases in the atmosphere. These rates are at least 1.9 times the rate of decline that has occurred in the 20th century, even under a modest warming scenario in which global temperature increases are limited to 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels.
Researchers have been creating three-dimensional computer models of individual glaciers for several years. But it’s only recently that increased processing power has made it possible to reconstruct ice cover across entire regions and mountain ranges, said Erik S. Mannerfelt, a glaciologist at Switzerland’s ETH University. Zurich who did not work on the new study.
“It’s a new era where we can look not at individual glaciers, but at populations” of them, he said.
Mr Mannerfelt is finishing a separate article that uses 22,000 photos taken by Swiss mountaineers between the two world wars to capture changes in Swiss glaciers since the early 1930s. equally detailed reconstructions of the ice in the islands of Tierra del Fuego in South America and in the Himalayas.
“Since we are now beginning to know exactly what happened,” Mr. Mannerfelt said, “we can make much better predictions for the future.”