Rising numbers of plant species on Europe’s mountain peaks might be hiding a growing problem: the loss of plants that are uniquely adapted to high elevations. Over the past few decades, global warming has reduced the impact of cold temperatures on plant life in mountainous regions, allowing more species to move upward and increasing overall biodiversity on summits. An international team of scientists, led by researchers from the University of Vienna and involving institutions like BOKU University and the Austrian Academy of Sciences, has found that while more species are now found on mountaintops, many specialized high-elevation plants are disappearing. This shift in plant communities suggests that the apparent increase in biodiversity is only part of the story. Until recently, the short growing seasons, low temperatures, and persistent frost on alpine summits made it difficult for many plant species to survive. However, as temperatures have risen, these challenges have lessened, allowing plants to colonize higher ground. This has led to a more diverse mix of species on mountain tops. Yet the study shows that while the number of species is increasing, the rate at which certain plants are vanishing is also rising. These lost species are often those that are uniquely adapted to the harsh conditions of high elevations. The research team analyzed plant life on 62 European mountain peaks, which had been surveyed four times between 2001 and 2022 as part of a global monitoring program called GLORIA. Their findings show that over time, the proportion of species not found in later surveys increased. Species that were originally centered around higher elevations were especially likely to disappear. The study, published in the journal Science, found that the rate of local extinctions increases with the amount of warming a region has experienced and near the lower edge of a species’ natural range. Scientists suggest that these local extinctions are driven by climate change. Johannes Wessely, the study’s lead author, explains that species are more likely to disappear from areas that have warmed the most. Harald Pauli, a researcher involved in the GLORIA program, adds that species already living in warmer parts of their range are more vulnerable to further temperature increases. These high-elevation specialists, which are often long-lived and adapted to extreme conditions, may not disappear immediately when their environment changes, leading to a delayed effect known as an "extinction debt." This delay might explain why new species are more frequently observed moving into alpine regions than old ones are being lost. The study suggests that current high extinction rates may be the result of environmental changes that began decades ago. While the findings hint that this "debt" may now be starting to be paid, further research is needed to confirm this interpretation.