Be prepared for bare ice in the Western Cwm and on the Lhotse flank – and for wide crevasses! That’s what you could say to mountaineers who want to try to climb Mount Everest this spring.
“The lack of snow, as I reported last winter as well, will lead to crevasses being less filled/more open and more bare ice slopes,” Mauri Pelto writes to me. “This can be altered by late winter/early spring storms, but that is not to be expected.” In the 2024 Everest spring season, the scientist had already pointed out a lot of bare ice and firn slopes in the Western Cwm and in the Lhotse flank and thus an increased risk of falling rocks. The Khumbu Glacier is currently in a similar condition (see image below).
Snow line rises even in winter
Since 1989, the professor of environmental sciences has been working at Nichols College in the small town of Dudley in the US state of Massachusetts. In his blog “From a Glaciers Perspective”, Pelto regularly describes how climate change is affecting glaciers around the world. Among other things, the glaciologist analyzes satellite images from NASA, which he constantly compares. This winter, for example, he determined that the snow line – i.e. the boundary between snow-covered and snow-free terrain – in the region around Mount Everest rose by around 150 meters between 11 December 2024 and 28 January 2025, i.e. within around one and a half months: from around 5,950 to 6,100 meters.
Pelto first observed the phenomenon of the rising snow line in winter in the Everest region in 2020/21, at that time by around 100 meters in altitude. Before that, the line had hardly moved or not moved at all, as the melting stopped in the cold season. Since 2021, however, even the Nangpa La (5,806 meters) and the Nup La (5,844 meters), two high passes on the eight-thousander Cho Oyu, have usually been completely or almost snow-free in January and February. The reason: increasingly drier and warmer winters, often combined with strong winds.
Evaporating snow at high altitudes
This causes the snow to melt – or “sublimate”, i.e. evaporate directly into water vapor at low temperatures (below plus 3.5 degrees Celsius). Sublimation is promoted by dry air, strong sunlight and strong winds. A study published in 2023 found that the snow cover on Everest in winter above 6,000 meters is lost primarily through sublimation: by up to 2.5 millimeters per day, i.e. one centimeter every four days.
Glacier melting as a result of climate change is frequently reported, but sublimation is rarely discussed. I ask Mauri Pelto what impact this form of snow loss is having on the retreat of the glaciers in the Himalayas. “When the glaciers are bare ice even in winter there is significant melting at lower elevations due to solar radiation below 5,500 m. Above 5,500 m sublimation becomes dominant,” answers the scientist, adding that sublimation alone does not lead to major losses. But if the snow loss by sublimation occurs instead of the usual winter snow accumulation, this means “a significant change in mass balance. Hence sublimation is less about retreat now more about thinning and then reduced flow through places like the Khumbu Icefall.”
So climate change is having an impact on Everest in several ways. None of them positive. Rather terrifying. And the effects on mountaineers are probably the least of the problems.
