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

Climate impacts on environmental systemsTable 3.1 Contributions to the sea-level budget since 1972Component 1972 to 2008 1993 to 2008(mm/year)(mm/year)Total from tide gauges 1.83 ± 0.18b 2.61 ± 0.55Total from tide gauges and altimeter 2.10 ± 0.16 3.22 ± 0.411. Thermal expansion 0.80 ± 0.15 0.88 ± 0.332. Glaciers and ice caps 0.67 ± 0.03 0.99 ± 0.043. Greenland ice sheet 0.12 ± 0.17 0.31 ± 0.174. Antarctic ice sheet 0.30 ± 0.20 0.43 ± 0.205. Terrestrial storage – 0.11 ± 0.19 – 0.08 ± 0.19Sum of components (1. + 2. + 3. + 4. + 5.) 1.78 ± 0.36 2.54 ± 0.46Source: Church and White, 2011.increase of between 0.18 m and 0.59 m from the1980–1999 mean to the 2090–2099 mean. Therange depends on both the spread in future GHGemissions and uncertainty from computer models.The largest sea-level rise contribution was projectedto come from the thermal expansion (0.10 to 0.41 m),followed by melting of glaciers and ice caps (0.07to 0.17 m) and Greenland ice sheet (0.01 to 0.12 m).The IPCC AR4 went further by including a simplesensitivity study, which allowed for future linearincreases in the dynamic ice sheet componentwith temperature. Whilst it is not clear that sucha relationship would be linear the calculationssuggest an additional 17 cm of rise could occurduring the 21st century. The report acknowledgedthat limitations in understanding and modelsmeant that it was not possible to provide with anydegree of confidence either a highest plausible21st century rise or central estimate of rise for all ofthe component sea-level terms.Since publication of the IPCC AR4, further progresshas been made in understanding and simulating sealevelchanges (Church and White, 2011). However,global physical models are still particularly limitedin their representation of ice sheet processes(Nicholls et al., 2010). Since current understandingsuggests that the potential for 21st century sealevelrise significantly above the AR4 range wouldlargely result from potential increases in the icesheet dynamical contributions, the lack of suitablephysically-based models is still a significanthindrance to making reliable projections.Statistical models of sea-level rise are alsoavailable. These models use observed relationshipsbetween changes in sea level and either surfaceair temperature or radiative forcing (Rahmstorf,2007; Vermeer and Rahmstorf, 2009). The statisticalmodels are then combined with 21st centuryprojections of radiative forcing or temperatureand used for projection purposes. Typically, theyproduce larger sea-level rise projections than currentphysically-based models. Future projections basedon this approach have limitations because thebalance of contributions to sea-level rise during thefuture may not be the same as the balance duringthe tuning period of these statistical relationships(Lowe and Gregory, 2010). However, the differencesbetween the two modelling approaches may also beinterpreted as indicating the scale of processes notwell represented in physically-based models.In view of these limitations to future projectionspurely from models, some studies have combinedunderstanding from current physical models withother strands of evidence to provide information onpossible high-end sea-level rise amounts. Evidencestands include maximum rates of sea-level rise at thelast interglacial and plausible kinematic constraintson future ice flows. A synthesis of high-end sea-levelrise estimates based on all sources of informationavailable is provided in Figure 3.7.The major conclusion from recent studies is thatit is still not possible to rule out GMSL increasesduring the next century of up to approximately 2 m.However, the balance of evidence suggests increasessignificantly in excess of 1 m are still consideredmuch less likely than lower rates of sea-level rise.This is consistent with the results of the ThamesEstuary 2100 study in the United Kingdom (Loweet al., 2009) and a recent study in the Netherlands(Katsman et al., 2011). The latter, for example,combined modelling and expert judgement to derivea plausible high‐end global scenario of 21st century106 Climate change, impacts and vulnerability in Europe 2012