Himalaya: Ice loss has doubled

"Roof of the World" has lost a good quarter of its glacial ice since 1975

The glaciers of the Himalayas have already lost 28 percent of their ice since 1975, here is a view of the Nup glacier near Mount Everest. © Joshua Maurer
Read out

Rapid wastage: The glaciers of the Himalayas have lost a good quarter of their ice since 1975. The annual ice loss on the "roof of the world" has now doubled, as revealed by a study. According to the report, about eight billion tons of ice melt every year in the Himalayas - meltwater would fill three million Olympic swimming pools each. The reason for the accelerated ice loss is primarily climate warming, as the researchers report in the journal "Science Advances".

The Himalaya is not only the highest mountain in the world, but also an important ice and drinking water reservoir of our planet. The glaciers of these mountains and the rivers they feed supply almost a billion people with water. But even on the "roof of the world" the glaciers are thawing. Only recently, climate researchers discovered that the Himalayas could lose two-thirds of its ice with unchecked warming.

Recording of the Khumbu region in the Himalayas, created in 1976 by the spy satellite Hexagon. © Josh Maurer / LDEO

Help of spy satellites

But how far has the ice shrinkage in the Himalayas progressed? And how fast does the glacier melt? So far, there were only punctual data for certain mountain areas and relatively short periods of time it simply lacked data. But now a new data source has opened up for climatologists: the now declassified images of US spy satellites from the desra of the Cold War.

Based on this satellite data, Joshua Maurer from Columbia University in New York and his colleagues were able to trace the development of 650 glaciers in the entire Himalayas from 1975 until today. For their study, they used the satellite imagery to create 3D digital models, which they used to determine and compare changes in ice thickness and glacier extent up to and beyond 2000.

A quarter of the ice is already gone

The result: "The glaciers of the Himalayas have lost considerable ice over the last 40 years, " the researchers report. The melting rate has since doubled in the period from 1975 to 2000. If the annual ice loss was still around 25 meters per year between 1975 and 2000, the roof of the world is already losing around 50 meters of ice per year, as the calculations have shown. This translates into eight billion tonnes of glacier ice to meltwater enough to fill 3.2 million Olympic swimming pools each year. display

All in all, the Himalayas have already lost a good quarter of their total ice: "The annual mass loss observed by us indicates that of the ice mass available in 1975, only 87 percent in the year 2000 and only 72 percent in 2016 brig were ", Maurer and his colleagues report. Nearly all areas of the Himalayas are affected by this ice loss, but the fastest thaw is the glaciers in the lower mountain regions.

Although the ice loss on the roof of the world progresses somewhat slower than in the Alps, the trend is the same, as the researchers emphasize.

The main driver is the warming

The new data also provide indications of the driving forces of this ice shrinkage. For some studies have suggested that in the Himalayas, factors such as monsoon and sedimentation on the glaciers play a particularly important role - possibly even stronger than that climate change. Whether this is true, Maurer and his team have examined by analyzing the melting rates of famous and uncontaminated glaciers, as well as the influence of precipitation.

It turned out that all types of glaciers - whether ru covered or clean, whether influenced by the monsoon or not - show the same trend towards accelerated ice loss, as the researchers report. This trend can also be seen in the entire, approximately 2, 000 kilometers long study area. But the only factor that is effective everywhere is the temperature rise of an average of one degree compared to the time from 1975 to 2000, state Maurer and his team.

According to the researchers, these results suggest that climate change is also the driving force of ice loss in the Himalayas. "The data look exactly as we would expect for a climate-related ice loss, " says Maurer. (Science Advances, 2019; doi: 10.1126 / sciadv.aav7266)

Source: Earth Institute at Columbia University

- Nadja Podbregar