12.4.2 Coastal and marine systems
Climate variability associated with the North Atlantic Oscillation (NAO) determines many physical coastal processes in Europe (Hurrell et al., 2003, 2004), including variations in the seasonality of coastal climates, winter wind speeds and patterns of storminess and coastal flooding in north-west Europe (Lozano et al., 2004; Stone and Orford, 2004; Yan et al., 2004). For Europe’s Atlantic coasts and shelf seas, the NAO also has a strong influence on the dynamic sea-surface height and geographic distribution of sea-level rise (Woolf et al., 2003), as well as some relation to coastal flooding and water levels in the Caspian Sea (Lal et al., 2001). Most SRES-based climate scenarios show a continuation of the recent positive phase of the NAO for the first decades of the 21st century with significant impacts on coastal areas (Cubasch et al., 2001; Hurrell et al., 2003).
Wind-driven waves and storms are seen as the primary drivers of short-term coastal processes on many European coasts (Smith et al., 2000). Climate simulations using the IS92a and A2 and B2 SRES scenarios (Meier et al., 2004; Räisänen et al., 2004) reinforce existing trends in storminess. These indicate some further increase in wind speeds and storm intensity in the north-eastern Atlantic during at least the early part of the 21st century (2010 to 2030), with a shift of storm centre maxima closer to European coasts (Knippertz et al., 2000; Leckebusch and Ulbrich, 2004; Lozano et al., 2004). These experiments also show a decline in storminess and wind intensity eastwards into the Mediterranean (Busuioc, 2001; Tomozeiu et al., 2007), but with localised increased storminess in parts of the Adriatic, Aegean and Black Seas (Guedes Soares et al., 2002).
Ensemble modelling of storm surges and tidal levels in shelf seas, particularly for the Baltic and southern North Sea, indicate fewer but more extreme surge events under some SRES emissions scenarios (Hulme et al., 2002; Meier et al., 2004; Lowe and Gregory, 2005). In addition, wave simulations show higher significant wave heights of >0.4m in the north-eastern Atlantic by the 2080s (Woolf et al., 2002; Tsimplis et al., 2004a; Wolf and Woolf, 2006). Higher wave and storm-surge elevations will be particularly significant because they will cause erosion and flooding in estuaries, deltas and embayments (Flather and Williams, 2000; Lionello et al., 2002; Tsimplis et al., 2004b; Woth et al., 2005; Meier et al., 2007).
Model projections of the IPCC SRES scenarios give a global mean sea-level rise of 0.09 to 0.88 m by 2100, with sea level rising at rates circa 2 to 4 times faster than those of the present day (EEA, 2004b; Meehl et al., 2007). In Europe, regional influences may result in sea-level rise being up to 50% higher than these global estimates (Woodworth et al., 2005). The impact of the NAO on winter sea levels provides an additional uncertainty of 0.1 to 0.2 m to these estimates (Hulme et al., 2002; Tsimplis et al., 2004a). Furthermore, the sustained melting of Greenland ice and other ice stores under climate warming, coupled with the impacts of a possible abrupt shut-down of the Atlantic meridional overturning circulation (MOC) after 2100, provide additional uncertainty to sea-level rise for Europe (Gregory et al., 2004; Levermann et al., 2005; Wigley, 2005; Meehl et al., 2007).
Sea-level rise can have a wide variety of impacts on Europe’s coastal areas; causing flooding, land loss, the salinisation of groundwater and the destruction of built property and infrastructures (Devoy, 2007; Nicholls and de la Vega-Leinert, 2007). Over large areas of formerly glaciated coastlines the continued decline in isostatic land uplift is bringing many areas within the range of sea-level rise (Smith et al., 2000). For the Baltic and Arctic coasts, sea-level rise projections under some SRES scenarios indicate an increased risk of flooding and coastal erosion after 2050 (Johansson et al., 2004; Meier et al., 2004, 2006; Kont et al., 2007). In areas of coastal subsidence or high tectonic activity, as in the low tidal range Mediterranean and Black Sea regions, climate-related sea-level rise could significantly increase potential damage from storm surges and tsunamis (Gregory et al., 2001). Sea-level rise will also cause an inland migration of Europe’s beaches and low-lying, soft sedimentary coasts (Sánchez-Arcilla et al., 2000; Stone and Orford, 2004; Hall et al., 2007). Coastal retreat rates are currently 0.5 to 1.0 m/yr for parts of the Atlantic coast most affected by storms and under sea-level rise these rates are expected to increase (Cooper and Pilkey, 2004; Lozano et al., 2004).
The vulnerability of marine and nearshore waters and of many coasts is very dependent on local factors (Smith et al., 2000; EEA, 2004b; Swift et al., 2007). Low-lying coastlines with high population densities and small tidal ranges will be most vulnerable to sea-level rise (Kundzewicz et al., 2001). Coastal flooding related to sea-level rise could affect large populations (Arnell et al., 2004). Under the SRES A1FI scenario up to an additional 1.6 million people each year in the Mediterranean, northern and western Europe, might experience coastal flooding by 2080 (Nicholls, 2004). Approximately 20% of existing coastal wetlands may disappear by 2080 under SRES scenarios for sea-level rise (Nicholls, 2004; Devoy, 2007). Impacts of climate warming upon coastal and marine ecosystems are also likely to intensify the problems of eutrophication and stress on these biological systems (EEA, 2004b; Robinson et al., 2005; SEPA, 2005; SEEG, 2006).