Rapid Melt of Himalayan Glaciers Exposed by Surveillance Satellite Imagery in an Alarming Manner

In a groundbreaking study, a team of researchers led by Joshua Maurer from Columbia University's Lamont-Doherty Earth Observatory has analysed Cold War-era spy imagery to uncover the extent of Himalayan glacier loss over the last four decades.

The team used declassified satellite imagery from the US spy program Hexagon, which had lain unused in archives for several years. They developed a computer software to turn the old photos into 3D maps, and compared these with modern satellite data from NASA and the Japanese space agency (Jaxa) to create the first detailed, four-decade record of ice along the 2,000km Himalayan mountain chain.

The study found that the melting of Himalayan glaciers has doubled since the turn of the 21st century, compared to the previous 25 years. Over 650 of the largest glaciers across India, China, Nepal, and Bhutan have lost the equivalent of a vertical foot and a half of ice each year this century. In the worst-hit areas, the ice loss can be as much as 5 metres a year.

The loss of ice is due to global heating caused by human activities. Warming air temperatures in the Himalayas have risen one degree Celsius higher than those from 1975 to 2000. Between 1975 and 2000, the average annual ice loss was approximately 25 cm, but this doubled to 50 cm in the 21st century.

The melting glaciers pose an impending threat to South Asia, as glaciers are a key source of fresh water for millions of people. Over 800 million people from China, India, Pakistan, and Bangladesh rely on seasonal Himalayan runoff for irrigation, hydropower, and drinking water.

Melting glaciers also pose the risk of disastrous floods, as glacial water can get blocked by piles of rubble and form glacial lakes that can burst and flood downstream areas. Even in a best-case scenario where the world rapidly decarbonises and becomes carbon neutral by 2050, limiting global warming to 1.5 degrees Celsius, the Himalayan glaciers are still melting rapidly and stand to lose a third of their total ice.

The study was published last February, and it reveals that the melting of Himalayan glaciers could alter local hydrology and disrupt water supplies, potentially leading to more severe water crises in densely populated areas. The researchers hope that their findings will raise awareness about the urgent need for action to combat climate change and protect these vital water sources.