The term “spy images” brings various associations to mind – from the Cold War to James Bond. However, we seldom associate them withtracking climate change. But recently, that is precisely what happened. Declassified Cold War-era spy satellite photographs have shown how much the melting of hundreds of Himalayan glaciers has accelerated in recent decades.
Why is Glacier Melt in the Himalayas Important?
The significance of the Himalayan glacier melt goes well beyond possibly losing a geological marvel. The natural, steady flow of meltwater from the glaciers is the primary (and often the sole) source of fresh water for hundreds of millions of people in the regions below the Himalayas. As feared, the recent studies of glacier mass from 2000 to 2016 have shown that these freshwater reservoirs are shrinking. The water security of the region is severely threatened, and predicting and projecting future glacier melt is critical for taking the right steps in mitigation.
To make precise predictions, scientists need to pinpoint all the reasons behind the ice loss. And there are plenty of circumstances at play. Warming of the region is an obvious one, but there are others, more discrete factors. They include changes in precipitation, and the black carbon deposition on the surface of the ice, which leads to a decreased albedo and faster warming of the ice surface.
The fact that there are several important variables and that some glaciers are melting faster than others makes it difficult to do the analysis and make predictions based on just a decade or two of observational data. That is why researches have turned onto the untapped resource – the spy images.
How Do Scientists Measure The Melt?
Back in the 1970s and 1980s, the U.S. government used twenty KH-9 military satellites to gather reconnaissance data from around the world; they took thousands of shots and ejected film capsules which parachuted to the ground. The photographs included the Himalayas. In 2011 they had been declassified and had become available to the public.
The additional worth of these images is that they can be used to make stereoscopic images – a relatively simple technique in which two pictures from different angles are combined to create a 3-D image. The research team led by Joshua Maurer, a glaciologist at Columbia University, did just that. They created an automated computer program which generated 3D snapshots of elevations across the Himalaya region from the available satellite images. Additionally, they applied the same approach to the data from NASA-Japanese satellite Terra, which collects data since 1999. They had analyzed 650 of the biggest glaciers.
With this data altogether, the researchers had an opportunity to observe and calculate the actual ice loss from 1975 to 2016. They estimated how much mass was lost by 2000 and then by 2016.
From 2000-2016, the average loss was about 0.43 metersof water per year, per glacier. Alarmingly, it is twice the rate for the period from 1975 to 2000, which was about 0.22 meters of water per year.
The increasing warming of the region seems to be the major driver of the melt. For this acceleration of melting, there would need to be an increase of somewhere between 0.4-1.4℃ for the period beginning in 2000, relative to 1975-2000. That is in tune with the air temperatures measured in the region, which now are about 1℃ higher than in the 1980s and 1990s.
Walter Immerzeel, a mountain hydrologist at Utrecht University in the Netherlands said that: “We did know already quite well the mass balance rates of the last two decades, but going this far back for the entire region is great,” and adds that it is “particularly interesting” to see that the ice mass loss has almost doubled from 2000-2016, in comparison to 1975-2000.
The new findings are in line with previous studies, which have also implicated that the main reason for the melting is the rising temperatures, while albedo and precipitation changes play a less significant role. However, other experts, such as Patrick Wagnon of the Institute of Research for Development in Grenoble, France, says that “There are a lot of uncertainties, and it’s much more complex than what’s shown here.”
The fact that the old spy images that have helped to add a few extra pieces to that complicated puzzle is unusually fascinating.
Maurer. J.M. et al., 2019. Acceleration of ice loss across the Himalayas over the past 40 years. Science Advances 19 Jun 2019. Vol. 5, no. 6, eaav7266. DOI: 10.1126/sciadv.aav7266 https://advances.sciencemag.org/content/5/6/eaav7266
Gramling, C. Cold War-era Spy Satellite Images Show Himalayan Glaciers Are Melting Fast. Science News. 19 June 2019 https://www.sciencenews.org/article/cold-war-spy-satellite-images-himalayan-glaciers-rapid-melting