Climate change, impacts and vulnerability in Europe ... - MemoFin.fr

Changes in the climate system2.3.4 GlaciersRelevanceGlaciers are particularly sensitive to changes in theglobal climate because their surface temperatureis close to the freezing/melting point (Zemp et al.,2006). When the loss of ice, mainly from melting andcalving in summer, is larger than the accumulationfrom snowfall in winter, the mass balance of theglacier turns negative and the glacier shrinks.Glaciers are an important freshwater resourceand act as 'water towers' for lower-lying regions.The water from melting glaciers contributes towater flow in rivers during summer months andthus helps maintain water levels for irrigation,hydropower production, cooling water andnavigation. The effects of a reduction in glaciersare, however, complex and vary from location tolocation (SGHL and CHy, 2011). Glacier melting alsocontributes to global sea-level rise (Radić and Hock,2011; Rignot et al., 2011).Past trendsA general loss of glacier mass has occurred in nearlyall European glacier regions (Figure 2.14). The Alpshave lost about two thirds of their ice mass since1850 (Zemp et al., 2005, 2006, 2008) and individualglaciers have faced even greater losses.Glaciers in different regions have been affectedsomewhat differently by recent climate change.In particular, Norwegian coastal glaciers wereexpanding and gaining mass up to the end of the1990s due to increased winter snowfall on the northAtlantic coast. Now these glaciers are also retreating(Andreassen et al., 2005; Nesje et al., 2008). Some icecaps at higher elevations in north-eastern Svalbardseem to be increasing in thickness (Bamber, 2004;Bevan et al., 2007), but estimates for Svalbard as awhole show a declining mass balance (Hagen et al.,2003; Kohler et al., 2007).The centennial retreat of European glaciersis attributed primarily to increased summertemperatures. However, changes in winterprecipitation, reduced glacier albedo due to the lackof summer snow fall and various other feedbackprocesses, such as the increasing debris cover on theglacier, can influence the behaviour of glaciers, inparticular on a regional and decadal scale.ProjectionsThe retreat of European glaciers is projected tocontinue throughout the 21st century. One studyestimates that the volume of European glacierswill decline between 22 and 66 % comparedto the current situation (all European regionscombined; Figure 2.15) (Radić and Hock, 2011).The relative volume loss is largest in the EuropeanAlps (76 ± 15 % standard deviation of 10 climatescenarios). In Norway nearly all smaller glaciersare projected to disappear and overall glacier areaas well as volume may be reduced by about onethird by 2100 even under the low SRES B2 emissionsscenario (Nesje et al., 2008). If summer airtemperatures were to rise by 3 °C and precipitationremained constant, the European Alps could loseabout 80 % of their average ice cover compared tothe period 1971–1990 (Zemp et al., 2006).Key messages: 2.3.4 Glaciers• The vast majority of glaciers in the European glacial regions are in retreat. Glaciers in the EuropeanAlps have lost approximately two thirds of their volume since 1850, with clear acceleration since the1980s.• Glacier retreat is expected to continue in the future. The volume of European glaciers has beenestimated to decline between 22 and 66 % compared to the current situation by 2100 under abusiness-as-usual emission scenario.• Glacier retreat contributes to sea-level rise and it affects freshwater supply and run off regimes,river navigation, irrigation and power generation. It may also cause natural hazards and damage toinfrastructure.80 Climate change, impacts and vulnerability in Europe 2012