According to research from the Wageningen University, climate change adds to existing risks for mountain climbers by increasing the likelihood of rocks falling.

For the study, published in the journal Geografiska Annaler, Arnaud Temme gathered climbing guides and used the information they provided to determine safety along climbing routes. Specifically, the climbing guides used for the study were for the Bernese Alps in Switzerland.

Aside from climbing routes, the guides contained information regarding the risks of falling rocks. For all of the routes analyzed, the orientation and type of rocks to be encountered were also noted.

Until now, most of the rock data available to mountain climbers are for small slopes or large rock avalanches. However, the climbing guides Temme used were made by generations of climbers documenting what they saw on their trips. The oldest of the guides examined for the study was 146 years old and this has allowed for the tracking of changes over a long period of time, many of which were linked by Temme to climate change.

A warming environment causes permafrost to thaw and snowfields and glaciers to retreat. This exposes more rocks to the air, increasing the likelihood that they'll fall or roll away because their stability has been reduced. With the permafrost degraded, thawing and freezing, rock cracks and crevices begin to shift. Each time water is frozen, it expands and a crack grows until a rock breaks.

While climate change does make mountain climbing more dangerous, Temme noted that there are also other factors at play that can account for increased danger for climbers, like the orientation of a slope.

As the eastern and western portions of a mountain are subjected to larger shifts in temperature, they appear to carry more risk. Again, the hotter the temperature, the more ice melts and the more rocks are exposed. Additionally, risks may be higher around areas with rocks and on faces of amphibolite and granite.

Given the effect of global warming on the Alps and other mountain areas, the temperature in a specific area can be used as an indicator of a route's risk level. Temme's research also highlights the role of historical knowledge in forecasting future risks for mountain climbers.

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