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

Changes in the climate systemFigure 2.13 Trend in yearly cumulated melting area of the Greenland ice sheet (1979–2011)Cumulated melt extent (1979 = 100 %)4003503002502001501005001979 1985 1991 1997 2003 2009Cumulated melt extent relative to 1979Note: Yearly cumulated area of the Greenland ice sheet showing melt during the period 1979 to 2011 relative to area in 1979.The linear trend 1979–2011 is included.Source: Fettweis et al., 2011.Ice is lost from Greenland, in roughly equalamounts, through surface melting and ice motion(van den Broeke et al., 2009). Surface meltingoccurs when warm air and sunlight first melt allthe previous year's snow and then the ice itself. Athigher elevations snow accumulates and the localmass balance remains positive. With global warmingthe height at which melting occurs moves upwardsand eventually a tipping point may be reached afterwhich the whole ice sheet starts to melt (Gregoryand Huybrechts, 2006).ProjectionsProjections of the surface mass balance of theGreenland ice sheet with many global climatemodels indicate that the 'tipping point' above whichthe Greenland ice decline will completely melt is aglobal temperature rise of about 3 °C (Gregory andHuybrechts, 2006). However, this estimate is subjectto considerable uncertainty (Bougamont et al., 2007).Climate models with an embedded dynamic icesheet model have suggested that a melt of 10–20 %of the current ice sheet volume, inducing ice loss insouthern Greenland, would lead to an irreversiblesea-level rise of about 1.3 m over several centuries.The addition of contributions by outlet glaciers(Ridley et al., 2005; Pfeffer et al., 2008) and theexpected surface mass balance-driven losses give anupper bound of about 19 cm sea-level rise from theGreenland ice sheet by 2100.Climate change, impacts and vulnerability in Europe 201279