Thaw on the roof of the world: climate change has even reached the highest mountain on earth. Measurements on Mount Everest show that its summit glacier has lost more than 55 meters of ice in the last 25 years. In addition, the ice layer thins out by a further two meters every year – and thus loses more ice every year than can accumulate in decades. If this trend continues, climbers could soon find more bare rock than ice and snow.
Be it the Alps, the Andes or the Himalayas – mountain glaciers are disappearing all over the world. Global warming, decreasing snowfall and local effects such as dark soot deposits on the light-colored ice surface are causing glaciers to shrink, sometimes rapidly. As a result, some mountain slopes are losing their stability and rockfalls and landslides are increasing. In the long term, the loss of glaciers also endangers the water supply of entire regions.
Expedition to the top of Mount Everest
However, a research team led by Mariusz Potocki from the University of Maine has investigated how badly the highest mountain peaks on the planet are affected by ice loss. For this purpose, the researchers undertook an expedition to the summit of Mount Everest in early summer 2019 and took an ice core from its summit glacier, the South Col Glacier, at an altitude of 8,020 meters. This makes it the ice core drilled from the greatest height and even got the team into the Guinness Book of Records.
In addition, the researchers installed an automatic weather station on the southern ascent route and on the so-called “balcony” – they are also the highest in the world. To accurately map the terrain, they also conducted the first-ever helicopter-borne LIDAR survey of Mount Everest’s summit. From the analysis of the ice core and the other data, Potocki and his team then reconstructed whether and how much ice and snow the world’s highest peak had lost.
Ice loss also at a good 8,000 meters altitude
The result: Even at the highest altitudes, Mount Everest loses more snow and ice than it gains. “The current loss rates are around two meters of water equivalent and suggest that as much ice is disappearing there in one year as has been accumulated over several decades,” report the researchers. At the same time, snowfall has also decreased by around 50 percent.
According to a supplementary model, the summit may have lost around 55 meters of ice over the past 25 years. This corresponds to the amount of ice that is typically deposited on Mount Everest over the course of 8,000 years. The decline of the summit glacier could have started as early as the 1950s. From about the year 2000, however, this ice loss accelerated again, as the team reports.
“These data answer one of the big questions of our Mount Everest expedition: whether the highest glaciers on the planet are affected by anthropogenic climate change,” says Potocki’s colleague Paul Mayewski. “The answer is a resounding yes!”
First snow removal, then sublimation
Unlike at lower altitudes, the loss of ice on the summit is due only to a small extent to melting of the ice. Instead, the scientists identified two other factors as the main drivers of glacier shrinkage: The removal of the snow cover by the wind initially exposes the ice surface and thus deprives it of its insulation. Then sublimation sets in – the ice becomes gaseous in the thin mountain air without first melting.
“This mechanism is important because our results suggest that the warmer air enhanced sublimation first of all. But the reduced humidity and the increasing winds at these altitudes also play an important role,” Potocki and his colleagues explain. In their view, these processes could also contribute to ice loss elsewhere in the highest elevations of the high mountains.
Changes already noticeable
“The highest glacier on Mount Everest demonstrates that even the roof of the world is now being affected by man-made climate change,” the researchers state. This has increasingly noticeable consequences for the peaks of the Himalayas and also for the mountaineers who want to scale them. The warming increases the risk of rockfalls and avalanches, as demonstrated by a deadly avalanche on Mount Everest in 2014.
“Warming will also change the experience of climbing Mount Everest as the dwindling ice and snow cover exposes more and more rock,” Potocki and his team say. Some routes could then be significantly more difficult to climb, others, like the Khumbu Icefall, become more dangerous. (NPJ Climate and Atmospheric Science, 2022; doi: 10.1038 / s41612-022-00230-0)
Quelle: University of Maine