Since 2000, Himalayan glaciers have been losing nearly half a meter of ice a year vertically on average.
Ice in the Himalayan mountains has been melting and visibly so. Melting snow is revealing the corpses of dead climbers who have laid buried in ice and snow for years and even decades.
Yet to see the true extent of ice melt over the past decades, a team of researchers from Columbia University in New York and the University of Utah examined high-resolution images taken by U.S. spy satellites during the Cold War. They then compared the images year by year from 1975 onwards for a decades-long overview of around 650 glaciers in the Himalayas.
They also created a 3D map with data on elevations and compared the results with images taken by high-tech NASA satellites. In their analysis, which spanned four decades of satellite observations in all, the scientists studied glaciers far and wide in India, China, Nepal and Bhutan.
Their findings indicate that since 2000 Himalayan glaciers have been losing nearly half a meter of ice a year vertically on average. In the final decades of the 20th century that loss was only around 22 centimeters a year, which indicates that climate change is accelerating snow melt in the Himalayas at a rate double what it was just a few decades ago.
The study indicates “that glaciers have been losing the equivalent of more than a vertical foot and half of ice each year since 2000 — double the amount of melting that took place from 1975 to 2000,” the researchers note. It is “the latest and perhaps most convincing indication that climate change is eating the Himalayas’ glaciers, potentially threatening water supplies for hundreds of millions of people downstream across much of Asia,” they add.
At higher elevations, where temperatures are naturally colder, there has been less loss of ice. Yet lower down, especially nearer ground level, glaciers are losing an alarming 5 meters of ice a year on average largely as a result of climate change, the researchers say.
The Himalayan glaciers have some 600 billion tons of ice locked up in them, which has earned the famous mountain range the moniker “the Third Pole.” Yet climate change is expected to melt much of that ice with perhaps two-thirds of the current ice cover gone within this century.
Most observations of the Himalayas, before this study, tended to focus on individual glaciers or certain regions or else examined glaciers only over a limited period of time. “These studies have produced sometimes contradictory results, both regarding the degree of ice loss and the causes,” the researchers explain.
“The new study synthesizes data from across the region, stretching from early satellite observations to the present,” they add. “The synthesis indicates that the melting is consistent in time and space, and that rising temperatures are to blame. Temperatures vary from place to place, but from 2000 to 2016 they have averaged 1 degree Centigrade (1.8 degrees Fahrenheit) higher than those from 1975 to 2000.”
Some researchers and critics have cautioned that ice might be melting for reasons other than increased temperatures. Lower levels of monsoon precipitation in some areas could also be blamed. Similarly, by burning vast amounts of fossil fuels, nations in the Himalayan region are releasing great amounts of soot into the sky, which then settles on snowy glacier surfaces where it absorbs sunrays and heats the ice below, causing it to melt.
The same, they posit, goes for Arctic sea ice, which has also been melting at accelerating speed, according to various studies. “Recent research suggests that only half of its decline has been due to anthropogenic forcing with the rest due to natural variability, with the latest data suggests that over the past decade its rate of loss has decreased compared to what it was 15-20 years ago,” one sceptic notes.
However, the new study’s authors stress that despite these factors they are convinced that it is a rise in temperatures that is primarily responsible for the accelerating extent of ice melt with warming being “the dominant driver of ice loss,” according to Joshua Maurer from Columbia University’s Lamont-Doherty Earth Observatory, who was the study’s lead author.
If so, the outlook for people living in the region appears bleak. With large volumes of fast-melting ice, local villages could be inundated by flash floods while permanent changes to local flora and fauna will cause marked shifts in local biodiversity.