Florence Magnin

Abstract Mountain permafrost, constituting 30% of the global permafrost area, is sensitive to climate change and strongly impacts mountain ecosystems and communities. This study examines 21st century permafrost warming in European mountains using decadal ground temperature data from sixty-four boreholes in the Alps, Scandinavia, Iceland, Sierra Nevada and Svalbard.

1 INTRODUCTION In the European Alps, the air temperature has increased by 2°C on average between the end of the 19th and the beginning of the 21st century, with an acceleration since 1980 (Beniston et al., 2018; Böhm et al., 2010; Nigrelli & Chiarle, 2023). High mountain environments are highly sensitive to this rapid climate change and the degradation of mountain permafrost is one of the consequences (Etzelmüller et al., 2020; Magnin et al., 2024).

1 INTRODUCTION Permafrost is recognised as an essential climate variable (ECV) by the World Meteorological Organization.1 Monitoring of permafrost temperature and active layer thickness (ALT, i.e., the depth of seasonal thaw) over long periods of time provides relevant information for understanding the impact of climate change on the cryospheric systems, the potential climate feedbacks through greenhouse gas release (e.g., Vonk and Gustafsson2), the implications for natural hazards driven by...