The European Alps in a changing climate: physical trends and impacts

Mountain areas crown their surrounding landscapes and host a great diversity of ecosystems and human activities. Due to their high altitudes and low temperatures, mountains, in many regions of the world, including Europe, allow the existence of the solid phase of water, ice, seasonally or perennially, which is found in glaciers, snow cover and permafrost, key components of the cryosphere. In the European Alps, the air temperature has increased by about 2 °C compared to the pre-industrial period (end of 19th century), alongside with a slight change in the seasonality of precipitation. Both are projected to intensify in the future. The increase in temperature induces profound changes for the mountain cryosphere with in particular the scarcity of snow cover, the retreat of glaciers and the thawing of permafrost. These changes are causing a cascade of upheavals for the water cycle, mountain ecosystems, the economic and touristic activity of mountain societies. They also induce changes in the natural hazards associated with the cryosphere such as avalanches, risks of glacial and peri-glacial origins as well as floods and droughts. Thus, in a changing climate, the fragile beauty and balance of the European Alps is undergoing profound disruptions whose consequences extend to the lowlands. These will continue to intensify as long as the temperature continues to rise and this is why every increment of temperature matters for the state of the European mountains.