The mammoth, 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 quickly as the rest of the Arctic region and seven times the global average. That is causing the islands’ glaciers to melt at an alarming rate, threatening polar bears and other wildlife, and adding to rising sea levels around the globe.
For a long time, though, predicting how quickly future warming might cause the ice to retreat took guesswork. In Svalbard and other places, most field measurements started only in the mid-20th century, and satellite observations even later.
Now, advances in computing are helping scientists bring old ice back to life in astonishing detail. Using black-and-white photos taken during mapping expeditions nearly a century ago, they are creating three-dimensional digital models of how the glaciers looked before modern record-keeping, and illuminating the ways they have changed over a longer stretch of time.
One of the largest such reconstructions to date, published Wednesday in the journal Nature, points to an unsettling conclusion: Svalbard’s glaciers could thin twice as fast in this century as they did in the last.
“Right now our predictions of future glacier change are not very grounded in all of the data that we already have from what’s happened in the last century,” said Emily C. Geyman, a graduate student at the California Institute of Technology and lead author of the new study. A deeper historical record lets scientists test how well their models of glacier changes line up with the past, Ms. Geyman said, before using them to peer into the future.
“This is a unique opportunity to look a bit further back in time,” said Ward J.J. 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 striking detail, how much some of the ice caps shrank between then and 2010. The average rate of loss was about 1.1 feet a year.
All across the frosty roof of the planet, rapid warming is upending lives and disrupting the vast wild landscapes. In its latest annual assessment of the Arctic, the U.S. National Oceanic and Atmospheric Administration found that shrinking sea ice and snow cover continued to transform the region last year. Collapsing glaciers have caused landslides and tsunamis. The thawing of permafrost, or continuously frozen ground, has destabilized homes and infrastructure built atop it.
Svalbard sits at the edge of the Arctic sea ice during winter, Dr. van Pelt said. Sea ice reflects much of the sunlight that hits it, so as the ice disappears, more solar energy gets absorbed by the ocean, heating the water. This is the main reason Svalbard is warming faster than the rest of the globe.
To reconstruct the islands’ past, Ms. Geyman and her co-authors used a trove of more than 5,500 aerial images taken by a Norwegian mapping project in 1936 and 1938. The icy conditions made flying a challenge, and the equipment was simple: a Zeiss camera mounted to a scout plane.
Still, the pictures, which are owned and managed by the Norwegian Polar Institute, a government research group, powerfully capture the drama of the landscape. “I was just enchanted by the photos,” Ms. Geyman said.
To transform the faded negatives into three-dimensional digital models, Ms. Geyman had to tell her computer how to interpret the images. This involved picking out points on different photos that show the same feature in the landscape — a crevasse, for instance, or a channel cut into the ice by meltwater — so the software could stitch the images together correctly.
All in all, she placed nearly 70,000 such points on the photos. It took the better part of two years. “I started to have to wear these glasses, I think,” she said, pointing at her face, “because of squinting so much at pixelated images on my screen.”
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In some places, 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 with ones made from more recent images to determine how much the ice had melted since the 1930s.
They then used these specifications to predict that the average elevation of Svalbard’s glaciers would shrink by between 2.2 and 3 feet a year before 2100, depending on the increase of greenhouse gases in the atmosphere. Those rates are at least 1.9 times the pace of retreat that occurred in the 20th century, even in a modest warming scenario in which global temperature increases are limited to 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels.
Researchers have been creating three-dimensional computer models of individual glaciers for several years now. But only recently have increases in processing power made it feasible to reconstruct ice sheets across entire regions and mountain ranges, said Erik S. Mannerfelt, a glaciologist at the Swiss university ETH Zurich who did not work on the new study.
“This is a new era where we can look not at individual glaciers, but at populations” of them, he said.
Mr. Mannerfelt is finishing a separate paper that uses 22,000 photos taken by Swiss mountaineers between the two world wars to capture changes in Switzerland’s glaciers since the early 1930s. He hopes that other image archives might enable similarly detailed reconstructions of the ice in South America’s Tierra del Fuego islands and in the Himalayas.
“Since we now are starting to know exactly what has happened,” Mr. Mannerfelt said, “we can make much better predictions for the future.”
Source : Nytimes