The gigantic, ethereally beautiful glaciers of Norway’s Svalbard archipelago, near the North Pole, bear the scars of climate change more than 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 faster than the global average. This is causing glaciers on the islands to melt at an alarming rate, threatening polar bears and other wildlife, and contributing to rising sea levels around the world.
However, for a long time, predicting how quickly future warming could lead to ice retreat required conjecture. On Svalbard and elsewhere, most field measurements began only in the middle of the 20th century, and satellite observations even later.
Now advances in computing are helping scientists bring old ice back to life in amazing detail. Using black-and-white photographs taken during mapping expeditions nearly a century ago, they create three-dimensional digital models of what glaciers looked like before modern records and show how they have changed over a longer period of time.
One of the largest such reconstructions to date, published Wednesday in the journal Nature, points to a disturbing conclusion: Svalbard’s glaciers could be thinning at twice the rate this century than they were last.
“Right now, our projections of future glacier changes are not very based on all the data we already have about what happened in the last century,” said Emily S. Gaiman, a Caltech graduate student and lead author of the study. new research. Deeper historical records allow scientists to test how well their models of glacial change fit with the past before using them to look into the future, Ms Gaiman said.
“This is a unique opportunity to look back a little,” said Ward JJ van Pelt, an associate professor at Uppsala University in Sweden who participated in the new study.
A 1936 reconstruction of the Svalbard glaciers by the group shows in startling detail how much some of the ice caps have shrunk from then until 2010. The average loss rate was about 1.1 feet per year.
Across the planet’s ice roof, rapid warming is changing lives and destroying vast wilderness landscapes. In its latest annual assessment of the Arctic, the US National Oceanic and Atmospheric Administration found that last year’s decline in sea ice and snow cover continued to transform the region. The collapse of the glaciers caused landslides and tsunamis. Melting permafrost, or permanently frozen ground, has destabilized homes and the infrastructure built on top of them.
According to Dr. van Pelt, in winter, Svalbard sits on the edge of Arctic sea ice. Sea ice reflects most of the sunlight that hits it, so when the ice disappears, more of the sun’s energy is absorbed by the ocean, warming the water. This is the main reason Svalbard is warming up faster than the rest of the globe.
To reconstruct the past of the islands, Mrs Geiman and her co-authors used a collection of more than 5,500 aerial photographs taken by the Norwegian Mapping Project in 1936 and 1938. The icy conditions made flying difficult, and the equipment was simple: a Zeiss camera mounted on a reconnaissance aircraft.
However, the photographs, which are owned and operated by the Norwegian Polar Institute, a government research group, powerfully capture the dramatic nature of the landscape. “I was just fascinated by the photographs,” Ms Gaiman said.
To convert the faded negatives into 3D digital models, Ms Gaiman had to tell her computer how to interpret the images. This involved selecting points in different photographs that show the same feature of the landscape—such as a crack or a channel cut by meltwater in the ice—so that the software could properly stitch the images together.
In total, she placed almost 70,000 such dots on the photographs. It took the better part of two years. “I think I had to wear these glasses,” she said, pointing to her face, “because I was squinting so hard at the pixelated images on my screen.”
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In some places, fresh white snow made it too hard to see the terrain in the photos, so she filled in the gaps with estimates.
After obtaining digital reconstructions of more than 1,500 glaciers on Svalbard, Ms Geiman and her co-authors compared them with reconstructions made from more recent images to determine how much ice has melted since the 1930s.
They then used these characteristics to predict that the average height of Svalbard’s glaciers would decline by 2.2 to 3 feet per year until 2100, depending on the increase in greenhouse gases in the atmosphere. These rates are at least 1.9 times the rate of retreat that took place in the 20th century, even under a moderate warming scenario that limits global temperature rise to 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels.
Scientists have been creating three-dimensional computer models of individual glaciers for several years. But it’s only recently that increases in computing power have made it possible to reconstruct ice sheets across entire regions and mountain ranges, said Eric S. Mannerfelt, a glaciologist at the Swiss university ETH Zurich, who was not involved in the new study.
“This is a new era where we can look not at individual glaciers, but at their populations,” he said.
Mr. Mannerfelt ends a separate article that uses 22,000 photographs 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 may allow similarly detailed reconstructions of the ice on the islands of Tierra del Fuego in South America and the Himalayas.
“Because we now begin to know exactly what happened,” Mr. Mannerfelt said, “we can make much more accurate predictions about the future.”