In March 2002, the Larsen B ice shelf catastrophically collapsed, breaking up an area about one-sixth the size of Tasmania.
In a paper published today in Scientific Reports, we used nearly 1,000 film photographs of Antarctica from the 1960s to reconstruct exactly what five glaciers looked like decades before the collapse of the Larsen B ice shelf. This allowed us to precisely calculate their contribution to sea level rise .
Although Antarctica is far away and the changing conditions may seem remote, the changes can have a profound impact on us all. Ice shelf removal can cause rapid melting of ocean glaciers and global sea level rise.
After consecutive years of unusually high temperatures, the Larsen B ice shelf collapsed during the week. This caused a dramatic change for the glaciers that flowed into it. The glaciers have been closely monitored since then – but few were observed before 2002.
However, the archive of over 300,000 historical images contains an invaluable record of the area from 1968 and has helped us gauge the difference between then and now.
NASA
Observation of glaciers
Ice shelves are thick floating bodies of ice attached to the coast of Antarctica. Melting ice shelves do not directly cause sea level rise.
However, ice shelves “hold back” the flow of glaciers. Once the shelves are removed, the glaciers melt rapidly into the ocean. This transports ice from land into the ocean and causes sea levels to rise.
In order to accurately predict how Antarctic ice sheets will respond to future climate change, it is important to understand how they have responded in the past. However, some places in Antarctica are so remote that it is almost disproportionately difficult and expensive to get there and collect data.
Scientists often look to satellites to collect data because it is relatively cheap and easy to do. However, persistent cloud cover on the Antarctic Peninsula can interfere with satellite observations for most of the year.
This means that for many areas in Antarctica, sightings are rare and often short-lived.
Historical photographs are an invaluable record
Between 1946 and 2000, United States Navy cartographers flew over nearly every corner of Antarctica and recorded 330,000 high-quality, large-format film photographs in an effort to map the continent.
Photo scans have been archived by the Polar Geospatial Center, University of Minnesota and are available for free download. These photos are as high resolution as many modern satellites can capture.
PGC, UMN
We created accurate, life-scale scaled 3D models of five glaciers in the Larsen B area using a technique called photogrammetry. Traditional photogrammetry uses two overlapping photographs from different angles to create a 3D surface – like how our two eyes can visualize objects in three dimensions.
Advances in computing now make it relatively easy to combine hundreds of overlapping photos. Matching points on overlapping photos are detected automatically and their 3D position is calculated geometrically. The precise surface of the glacier can then be created from a cloud of millions of corresponding points.
Identifiable features in the images with known coordinates, such as nearby mountain peaks or uniquely shaped boulders, can then be assigned a GPS point to reduce the model.
Then and now
After comparing five glaciers in 1968 and 2001 (the latter just a few months before the collapse), we found that they were relatively unchanged.
After the collapse, the glaciers lost 35 billion tons of ice on land. 28 billion tons were lost from one large glacier, equivalent to about 0.1 mm of global sea level rise.
That doesn’t sound like much, but it’s the result of one iceberg from one event. In other words, it’s the equivalent of every person on Earth tipping over a liter bottle of water every day for ten years.
These images were essential for high-resolution observations of glaciers decades before they were affected by ice shelf collapse.
New Antarctic record
As climate change accelerates, atmospheric and ocean warming threatens the remaining ice shelves on the Antarctic Peninsula. The historical image archive will become increasingly important for expanding the record of change and finding out how much things change.
The same images could be used to investigate other ice shelves or glaciers, coastal changes, penguin colonies, vegetation expansion, or even direct human impacts.
The historical image archive is an invaluable resource waiting to be tapped.