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

Climate impacts on environmental systemsRates of global mean sea-level (GMSL) rise havebeen estimated at approximately 3 mm/year sincearound the mid-1990s (Church and White, 2011).This is greater than the longer term rise during the20th century of around 1.7 mm/year, which is shownin Figure 3.6. There is evidence that the contributionfrom the melting cryosphere has increased recently(Velicogna, 2009). Both for recent decades and overthe longer term historical period, there is somevariability evident about the trend. In particular,there are periods during the 20th century beforethe 1990s where the rate of sea-level rise may havereached the recent rate of 3 mm/year for some years,although the higher rates of sea-level rise weregenerally sustained for shorter periods than recently.For a very recent time period, the variability in sealevel includes a notable dip, starting in 2010. It hasbeen suggested, based on observations from theGRACE satellite, that this observed recent dip insea level may be related to the switch from El Niñoto La Niña conditions in the Pacific and associatedchanges in precipitation patterns and storage ofwater on land (NASA, 2012).It is not yet clear from observations whether thegenerally increased rate of sea-level rise observedsince the mid-1990s will continue into the future.The many observations of surging outlet glaciers andice streams (which could lead to high future ratesof sea‐level rise) must be balanced by recent workshowing that some outlet glaciers on the Greenlandice sheet have now either stopped accelerating oreven slowed down (Joughin et al., 2010). Modellingwork of individual ice sheet glaciers also shows thepotential for decadal and multi-decadal variabilityin glacier flow (Nick et al., 2009). There is sufficientevidence, based on recent observations, to beconcerned about the possibility for an increase in therate of sea-level rise to 2100 beyond that projectedby the models used in the IPCC AR4 (IPCC, 2007)(see Figure 3.7). However, a greater understandingof the potential for accelerated ice sheet dynamicalprocesses that could give rise to such rapid sea-levelrise is needed from improved physically-basedmodels and from appropriate palaeo observationsbefore more precise and reliable estimates of futuresea-level rise can be made.Figure 3.6 Change in global mean sea level from 1860 to 2009Sea level (mm)100500– 50– 100– 150– 200– 2501880 1900 1920 1940 1960 1980 2000GMSL _RECONS (mm) (Reconstruction, 1880 to 2009, yearly)GMSL_ALT (Satellite altimeter data, 1993 to 2009, yearly)Note:Global mean sea level from 1860 to 2009 as estimated from coastal and island sea-level data (1880–2009, blue, withuncertainty range) and from satellite altimeter data (1993–2009, grey).Source: Church and White, 2011.Climate change, impacts and vulnerability in Europe 2012103