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

Climate impacts on environmental systems3.2.2 Global and European sea-level riseRelevanceSea level is an important indicator of climate changebecause it is associated with significant potentialimpacts on settlements, infrastructure, people andnatural systems. It acts on time scales much longerthan those of indicators that are closely related tonear-surface temperature change (see Section 2.2).Even if GHG concentrations were stabilisedimmediately, sea level would continue to rise forcenturies.Low-lying coastlines with high population densitiesand small tidal ranges are most vulnerable tosea-level rise, in particular where adaptation ishindered by a lack of economic resources or byother constraints. In Europe, the potential impacts ofsea-level rise include flooding, coastal erosion, andthe loss of flat coastal regions (EEA, 2010). Risingsea levels can also cause salt-water intrusion intolow-lying aquifers and endanger coastal ecosystemsand wetlands. Higher flood levels increase the risksto life and property, including sea dikes and otherinfrastructure, with possible follow-up effects ontourism, recreation and transportation functions.Damage associated with sea-level rise wouldfrequently result from extreme events, such as stormsurges, the frequency of which would increase as themean sea-level rises (see Section 3.2.3).Changes in global average sea level result from acombination of several physical processes. Thermalexpansion of the oceans occurs as a result ofwarming ocean water. Additional water is added tothe ocean from a net melting of glaciers and smallice caps, and from the large Greenland and WestAntarctic ice sheets. Further contributions may comefrom changes in the storage of liquid water on land,either in natural reservoirs such as groundwater orman-made reservoirs.The locally experienced changes in sea level differfrom global average changes for various reasons.Changes in water density are not expected to bespatially uniform, and changes in ocean circulationalso have regionally different impacts. At anyparticular location there may also be a verticalmovement of the land in either direction, forexample due to the post-glacial rebound (in northernEurope) or to local groundwater extraction.Past trendsSea-level changes can be measured using tidegauges and remotely from space using altimeters.Many tide gauge measurements have longmulti‐decade time series, with some exceeding morethan 100 years. However, the results can be distortedby local effects. Satellite altimeters enable sea levelto be measured from space and give much betterspatial coverage (except at high latitudes). However,the length of the record is limited.Key messages: 3.2.2 Global and European sea-level rise• Tide gauges show that global mean sea level rose at a rate of around 1.7 mm/year over the20th century, but there has been significant decadal variations around this value.• Satellite measurements show a rate of global mean sea-level rise of around 3 mm/year over the last2 decades.• Sea level is not rising uniformly at all locations, with some locations experiencing much greater thanaverage rise.• Projections of global mean sea-level rise in the 21st century range between 20 cm and about 2 m.Modelling uncertainty contributes at least as much to the overall uncertainty as uncertainty about futureGHG emissions scenarios. It is likely that 21st century sea-level rise will be greater than during the20th century. It is more likely to be less than 1 m than to be more than 1 m.• Coastal impacts also depend on the vertical movement of the land, which can either add to or subtractfrom climate-induced sea-level change, depending on the particular location.102 Climate change, impacts and vulnerability in Europe 2012