Mountains, especially in the tropics, harbor a unique and large portion of the world’s biodiversity. Their geographic isolation, limited range size, and unique environmental adaptations make montane species potentially the most threatened under impeding climate change. Here we provide a global baseline assessment of extinction risk for high-elevation specialists in a future warmer world. We consider three dispersal scenarios for simulated species with different vertical and lateral geographic range sizes, and for the world’s 1,009 montane bird species.

Results/Conclusions

Under constrained vertical dispersal, species with narrow vertical distributions are strongly impacted; at least a third of montane bird diversity is severely threatened. Additional risk factors include limited range size and occurrence on certain lower mountain systems or mountains at high northern latitudes. In a scenario of unconstrained vertical dispersal, the location and structure of mountain systems emerges as a strong driver of extinction risk. Even unconstrained lateral movements in response to climate change offer little improvement to the fate of montane species in the Afrotropics, Australasia, and Nearctic. Our results demonstrate the particular roles that the geography of species richness, the spatial structure of lateral and particularly vertical range extents, and the specific geography of montane systems have in determining the vulnerability of montane biodiversity to climate change. Our findings confirm the outstanding levels of biotic perturbation and extinction risk that mountain systems are likely to experience under global warming and highlight the need for additional knowledge on species’ vertical distributions, dispersal and adaptive capacities.