Astonishing Cold War spy satellite images reveal extent of Himalayan glacier loss

Sean Morrison

Astonishing images from Cold War spy satellites have revealed the dramatic rate at which Himalayan glaciers are melting.

Scientists compared photographs taken by a US reconnaissance programme with recent spacecraft observations.

Their analysis of observations across India, China, Nepal and Bhutan found that the melting has doubled over the past 40 years.

The experts said the main cause was climate change.

Analysis from 40 years of satellite observations across India, China, Nepal and Bhutan shows loss of ice from the glaciers in the region (PA)

Some of the images used were from military satellites in the 1970s, which took thousands of pictures worldwide before ejecting film recovery capsules and parachuting them to Earth over the Pacific.

The scientists used the recently declassified spy satellite photographs to create 3D models and combined them with modern satellite imagery to produce a consistent set of data showing the changing elevation of glaciers over time.

They quantified the ice loss trends for 650 of the largest glaciers along a 2,000km (1,240 miles) sweep of the Himalayas from Spiti Lahaul, northern India to Bhutan, which account for around 55 per cent of the region's total amount of ice.

Ice loss from glaciers is important because it contributes to rising sea levels.

The glaciers high in the Himalayan Mountains are also an important source of water for drinking, agriculture and hydropower for hundreds of millions of people downriver in south Asia.

Results from the comprehensive study published in the journal Science Advances indicate that ice was being lost twice as fast in the period 2000-2016 compared to 1975-2000, and the trend was consistent across the region - suggesting a warmer climate was the main driver, researchers said.

The thickness of the ice had shrunk by around 43cm a year on average in the 21st century, around twice the rate seen between 1975 and 2000.

Researchers estimated that less than three-quarters (72 per cent) of the total amount of ice present in the region in 1975 was still there in 2016.

Lead author Joshua Maurer, from Columbia University's Lamont-Doherty Earth Observatory said: "This is the clearest picture yet of how fast Himalayan glaciers are melting over this time interval, and why."

While other factors such as changes in rainfall and increase in soot from industry landing on the ice and speeding up melting could be playing a role, the researchers said temperature was the overarching force.

Data from weather stations in the high mountains of Asia have recorded temperature increases of around 1C between 2000 and 2016.

The team compiled temperature data from the study period and calculated the amount of melting the warming conditions would be expected to produce - which matched the figures for what happened, the scientists said.

Mr Maurer said: "It looks just like what we would expect if warming were the dominant driver of ice loss."