Mountain regions are hotspots of immense species richness, contributing disproportionately to terrestrial biodiversity and endemism globally while representing an overall small area of land. Climate change-induced warming represents a threat to the significance and influence of mountains as hosts for biodiversity as species’ ranges will need to shift accordingly to follow changes in their thermal niches. Global warming acts as an escalator to extinction for species that live on mountains; species move to higher elevations as temperature increases, pushing out those living on mountaintops altogether.

Mountain regions are home to roughly 87% of terrestrial global diversity while occupying only 25% of all land area (excluding Antarctica); of this 87%, an overwhelmingly large amount of species are defined as “mountain endemic”, a species with 90% or more of its distribution in mountain ranges. Endemic species face greater risk of extinction compared to broadly distributed species because of their limited geographical range to a singular location. A study conducted on the Bale Mountains in Ethiopia, one of the 34 biodiversity hotspots on Earth, revealed staggering predictions for the fate of endemic species under climate change. They found a temperature increase by 3° C or 4° C predicted the local extinction of about 36% of all endemic species, which is well within the reality of current projections of global climate change.

Mountain top extinction is of particular concern for endemic species that do not have populations on other high mountains or low latitudes. Area is one of the most important factors in defining species richness; on conical mountains, area tends to declines as elevation increases, so, species richness will steadily decline with elevation. As climate change shifts ranges up-slope, summit-based species will not have higher elevations to receive them, resulting in a potential extinction.

Mountaintop extinction will likely take place more frequently in tropical latitudes, where temperature exerts a stronger influence on a species’ range limit due to the flat latitudinal gradient in temperature compared to the temperate zone which has a much steeper latitudinal gradient. The effects of vulnerability in high elevation species are already apparent in the russet-crowned warbler, a high elevation bird atop the Panticolla Transect in the Andes - as a result of shifts in its lower limit near the top of the ridge, its population has declined an estimated 72%.

Mountain regions greatly affect vertebrate species and global diversity. (Source: Science Magazine)

The biodiversity of mountains varies remarkably on a global scale. Low latitudes experience hyper-diversity, though some are not exceptionally so; however, in arctic and temperate zones, mountain species diversity barely surpasses that of adjacent lowlands. Regardless, climate change is expected to substantially reduce the extent and richness of species home to Arctic-alpine regions. In Fennoscandia, Northern Europe (55°N to 72°N) a study examining the sensitivity of 164 high-latitude mountain species predicted the average richness of mountain flora will decrease by 15% to 47% per 1 km² cell, depending on the climate scenario, and that a staggering 71% to 92% of the considered species are expected to lose over half of their range by 2100.

A hill-shade map displays topographic relief through global patterns of vertebrate richness in lowland and highland areas. (Source: Science Magazine)

Climate change is of specific concern for mountain regions due to the climatic characteristics of mountains playing a key role in generating and maintaining the extremely pronounced patterns of species diversity. Several factors stand out in differing mountain climates from those of the lowlands: topographical complex tropical mountains contribute to an abundance of different climate types, the complexity of the elevational gradient brings starkly distinct climate zones in close proximity, and temporal scales of short-term and long-term climate oscillations is unique. A slight change in any of these factors can push the response adaptation, movement, or extinction.

All of these findings provide evidence that climate change will substantially diminish the richness and alter the distribution patterns of flora and fauna on mountain ranges in the future. Conservation strategies should target these hyper-diverse areas in an effort to mitigate loss to diversity. It is clear that further research focusing on the specific impacts of climate change and anticipation of range shifts in these environments is necessary.