Understanding spatial patterns of elevation-dependent climate change and associated impacts in mountain regions of Europe and the world.

Mountain systems in Europe and around the world are known to be experiencing more rapid environmental changes than many other ecosystems, but our knowledge of, and ability to predict, future changes is hampered by lack of integrated long-term monitoring systems at high elevations and in areas of complex terrain. An analysis of the elevational distribution of weather stations in Europe shows bias towards lower elevations. This is unfortunate since physical theory suggests that future climate change will be elevation-dependent, with often faster warming observed and predicted at high elevations. Elevation-dependent climate change (EDCC) occurs for many reasons including the decline of the cryosphere and snow-albedo feedback effects, changes in ecological zonation including migration of treelines, physical changes in the temperature and moisture structure of the free atmosphere which will enhance high altitude warming, and the influence of aerosol deposition on the surface, including on snow. Although the mechanisms and drivers of elevation dependent climate change are quite well known, the exact way in which these currently combine in the mountain systems of Europe is unclear, with many regional differences in observed trends in climate variables being evident. A metanalysis of the literature on climate changes observed within the Greater Alpine Region (GAR) is presented. Examples of research studies in contrasting European mountain regions, from the Alps to the Scandes in northern Finland, are also presented. The effects of enhanced climate changes on the mountain ecosystem include influences on ecological zonation and the migration of species upslope. Changing lapse rates and uneven warming with elevation will alter the elevational extent of ecological zones, either expanding or compressing them. There will be additional impacts on cryospheric and hydrological systems, including rising snowlines, and a change from snow dominated to rain dominated watersheds. The hydrological regime in many mountain systems will become more variable, and dominated by precipitation events rather than by snowmelt. This will make runoff more variable and less easy to manage for human systems. Additional changes in hazard and risk in mountain systems, include increased flooding, periods of low flow, risk of extinction events in high elevation ecosystems, and increased rockfalls and landslides as a result of increased heavy precipitation events. All these will have consequences for human systems in mountain regions. An interdisciplinary approach is required to address such changes and mitigate against future adverse consequences on ecological and human systems. Future recommendations for scientific advances are proposed and discussed, including the identification of Essential Mountain Climate Variables (EMCVs), the development of integrated interdisciplinary Mountain Observatories (MO), and a consistent protocol for the monitoring of long-term change over the elevation gradient (the Unified High Elevation Observation Platform or UHOP). Many such initiatives are already underway, facilitated by the Mountain Research Initiative (MRI).