12.4.3 Mountains and sub-Arctic regions
The duration of snow cover is expected to decrease by several weeks for each °C of temperature increase in the Alps region at middle elevations (Hantel et al., 2000; Wielke et al., 2004; Martin and Etchevers, 2005). An upward shift of the glacier equilibrium line is expected from 60 to 140 m/°C (Maisch, 2000; Vincent, 2002; Oerlemans, 2003). Glaciers will experience a substantial retreat during the 21st century (Haeberli and Burn, 2002). Small glaciers will disappear, while larger glaciers will suffer a volume reduction between 30% and 70% by 2050 (Schneeberger et al., 2003; Paul et al., 2004). During the retreat of glaciers, spring and summer discharge will decrease (Hagg and Braun, 2004). The lower elevation of permafrost is likely to rise by several hundred metres. Rising temperatures and melting permafrost will destabilise mountain walls and increase the frequency of rock falls, threatening mountain valleys (Gruber et al., 2004). In northern Europe, lowland permafrost will eventually disappear (Haeberli and Burns, 2002). Changes in snowpack and glacial extent may also alter the likelihood of snow and ice avalanches, depending on the complex interaction of surface geometry, precipitation and temperature (Martin et al., 2001; Haeberli and Burns, 2002).
It is virtually certain that European mountain flora will undergo major changes due to climate change (Theurillat and Guisan, 2001; Walther, 2004). Change in snow-cover duration and growing season length should have much more pronounced effects than direct effects of temperature changes on metabolism (Grace et al., 2002; Körner, 2003). Overall trends are towards increased growing season, earlier phenology and shifts of species distributions towards higher elevations (Kullman 2002; Körner, 2003; Egli et al., 2004; Sandvik et al., 2004; Walther, 2004). Similar shifts in elevation are also documented for animal species (Hughes, 2000). The treeline is predicted to shift upward by several hundred metres (Badeck et al., 2001). There is evidence that this process has already begun in Scandinavia (Kullman, 2002), the Ural Mountains (Shiyatov et al., 2005), West Carpathians (Mindas et al., 2000) and the Mediterranean (Peñuelas and Boada, 2003; Camarero and Gutiérrez, 2004). These changes, together with the effect of abandonment of traditional alpine pastures, will restrict the alpine zone to higher elevations (Guisan and Theurillat, 2001; Grace et al., 2002; Dirnböck et al., 2003; Dullinger et al., 2004), severely threatening nival flora (Gottfried et al., 2002). The composition and structure of alpine and nival communities are very likely to change (Guisan and Theurillat, 2000; Walther, 2004). Local plant species losses of up to 62% are projected for Mediterranean and Lusitanian mountains by the 2080s under the A1 scenario (Thuiller et al., 2005). Mountain regions may additionally experience a loss of endemism due to invasive species (Viner et al., 2006). Similar extreme impacts are expected for habitat and animal diversity as well, making mountain ecosystems among the most threatened in Europe (Schröter et al., 2005).