The high Alpine landscape is significantly shaped by glacial and periglacial processes. It is sensitive to effects caused by global warming, such as glacier retreat and permafrost degradation. Trails and mountain huts form the infrastructure basis for hiking and mountaineering in the Alps. This infrastructure is a decisive factor for summer mountain tourism. This article presents a classification of phenomena describing the effects of global warming on high Alpine trails and routes. The classification was developed based on an in-depth study in the Austrian Alps. The examples collected show that in the context of global warming, numerous different types of phenomena can affect both the occurrence of natural hazards along high Alpine trails and routes, and the accessibility of the terrain. Depending on the specific situation, threats and difficulties can increase or decrease. Trail holders have to adapt the high Alpine trail network to these changes. The classification presented here can serve to support maintenance of the Alpine trail network in the future.