The Larsen Ice Shelf in Antarctica has been breaking up for decades, but the 2002 Larsen B collapse was particularly dramatic. After being stable for at least 10,000 years, a large part of the shelf broke up, with consequences felt across the planet.
Widespread changes in Antarctica have been widely studied and published, but contextualizing and analyzing how changing conditions in Antarctica affect the rest of the world has been challenging. To combat this, scientists have used film footage from the 1960s to help understand how the collapse of Antarctic ice sheets has affected global sea levels.
In a research paper published in Nature, Ryan North and Timothy T. Barrows investigate historic film photos of Antarctica dating back to the 1940s and apply a sophisticated modern analytical technique called structure-from-motion (SfM) photogrammetry. The researchers say, “The technique creates digital elevation models (DEMs) by constructing 3D point clouds of matching features in overlaid photos without needing the original camera positions or orientations.”
As North and Barrows explain in an article on Conversationaccurate understanding of the past is essential to predicting the future.
“To accurately predict how Antarctic glaciers will respond to future climate change, it is critical to understand how they have responded in the past,” the researchers write.
A significant challenge is that Antarctica is remote and capturing good data there is prohibitively expensive. While satellites are excellent for collecting data on most of the Earth’s surface, the Antarctic Peninsula is covered by clouds for most of the year. The result is that observations of the area are irregular and short-term.
However, US Navy cartographers captured more than 300,000 aerial photographs of Antarctica, all of which are freely available at the Polar Geospatial Center at the University of Minnesota, as part of a large-scale effort to map the continent from 1946 to 2000. .
Large format film photos are extremely high resolution, so North and Barrows applied SfM photogrammetry to 871 specific photos from 1968 to build historical data for the Larsen B region.
The selected photographs were captured on large format 9×9 grayscale film on December 21, 23, and 27, 1968. The film was then scanned at 1000 DPI by the United States Geological Survey (USGS). 503 of the 867 photos were used to build data for the Jorum, Crane, Mapple and Melville glaciers, while more than 360 were used to determine the elevation of the Flask glacier. Images were also manually adjusted to reduce errors in the photogrammetric process, including changes in cropping, exposure, contrast, and sharpness.
“We use historical DEMs to accurately measure the net change in surface elevations of the Larsen B branch glaciers (Jorum, Crane, Mapple, Melville and Flask) between 1968 and 2021. For the same glaciers, we also calculate changes in surface elevation between 1968 and 2001… Using accurate elevation differences, we provide new estimates of mass balance and sea level contribution spanning 53 years and discuss these measurements in the context of the existing precollapse and postcollapse literature ,” they explain.
As a result of their research, the pair determined the precise elevation changes across discrete regions of Larsen B and detailed the extremely small changes over the decades that eventually led to the ice shelf’s collapse. They found that after the 2002 Larsen B collapse, the glaciers lost 35 billion tons of ice to land. The largest glacier alone lost 28 billion tons, which resulted in the Earth’s sea level rising by about 0.1 millimeters.
“That doesn’t sound like much,” admit the researchers. “But it’s the result of a glacier from an event. Put another way, it’s the equivalent of every single person on Earth throwing away a one-liter water bottle every day for 10 years.”
North and Barrow call the historic archive of aerial film photographs an “invaluable resource waiting to be tapped” and say the same process they used for this investigation could be used to analyze other ice shelves or glaciers. , penguin colonies, the expansion of vegetation or even direct human activity.
Antarctic ice shelves and glaciers will continue to evolve as climate change accelerates, affecting the rest of the planet. Of course, one of the most critical steps toward addressing the issue requires understanding the problem itself.
Image credits: Unless otherwise noted, photos in this article are courtesy of the Polar Geospatial Center and the United States Geological Survey. The referenced research is “High-Resolution Elevation Models of Larsen B Glaciers Derived from 1960s Imagery,” written by Ryan North and Timothy T. Barrows.