Global reduction of snow cover in ski areas under climate change

which is why other approaches are more useful when evaluating snow cover area more locally [55–57]. In addition, we showed the results for three different global emissions pathways, while focusing on a high emissions scenario. Although there is contrasting evidence in the lit- erature on which emissions pathways tracks current trajectories best [29–31], the very high emissions scenario (SSP5-8.5) is unlikely to be met. However, since mountain systems are par- ticularly sensitive to climate warming, projecting the results for the high and very high emis- sions scenario is likely to be more relevant compared to other systems. Our results indicate space contractions in present ski areas. Overall, less ski areas will remain snow reliable under future climate conditions and hence, skiable areas will be concen- trated to spatially restricted higher elevations. Additionally, we show that areas in highly popu- lated areas are most affected by climate change. Thus, future ski areas will concentrate towards less populated areas, although it is important to mention that this analysis relies on a constant population density, which is highly unlikely in the future. In fact, population density is pro- jected to increase for mountain areas under SSP3 [58]. Such an increase in population density could imply more pressure on alpine ecosystems in the long-term, in addition to the threat of ski area expansions in high-altitude ecosystems. This trend to expand towards higher and more remote areas is not yet quantified, but well demonstrated in our results. Consequently,

an increase in transportation efforts is likely as people who were formerly skiing in near and low altitude areas will have to travel towards the inner parts of the mountain ranges and towards higher altitudes. The combination of a concentration of ski areas towards higher alti- tudes and the resulting expansion of infrastructure to enable access to skiable areas is addition- ally of concern for mountain biodiversity. High altitudes are known to be a biodiversity hotspot and serve as refuge for vulnerable species, which might be directly affected by the expanse of ski areas and the increase in ski tourists. Alpine plants are known to only slowly recover from disturbances [20]. Moreover, indirect effects on alpine species are likely. For instance, ski areas are associated with an anticipation of plant phenology [50], potentially inducing a mismatch between plant blooming and herbivore activity [59]. Biodiversity conser- vation should be aware of the potential trajectories, not only of climate warming per se, but also of the implications of climate change for skiing. We expect conflicts between nature and skiers to increase with ongoing climate change. We project substantially reduced snow reliability in current ski areas on a global scale and an overall reduced number of skiable areas worldwide. Additionally, we show that coastal, low-latitudinal regions and highly populated areas, as well as outer and lower parts of the mountain ranges, are more affected by climate change. Therefore, we conclude that whilst the

ski market is not projected to decrease in the near future, higher elevated and less populated ski areas will be expanding in size and infrastructure. These developments are alerting for the nature in mountain areas, as spatial compromises will most likely have to be made between future skiable areas and space for conservation of alpine biodiversity. Supporting information S1 Table. Annual snow cover days (mean, median, 5% and 95% confidence interval) per time period and in seven major mountain skiing areas under a high (SSP3-7.0) emissions scenario. (PDF) S2 Table. Annual snow cover days (mean, median, 5% and 95% confidence interval) per time period and in seven major mountain skiing areas under a very high (SSP5-8.5) emis- sions scenario. (PDF) PLOS ONE Global reduction of snow cover in ski areas under climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0299735 March 13, 2024 9 / 15