Rising seas and retreating coastlines

Any rise in the mean sea level will result in the retreat of unprotected coastlines(Bruun 1962). Fortunately, the still-stand (slow) conditions of global average sealevel rise (SLR) during the last century has resulted in slow and mostly manageablecoastline retreat (recession). Alarmingly, however, recent research indicates that theglobal average sea levels may rise at an unprecedented rate during the twenty-firstcentury (Leuliette et al. 2004; Beckley et al. 2007). The latest IPCC projections (IPCC2007) indicate an SLR range from 0.18 to 0.79 m by 2090–2099 relative to 1980–1999, including an allowance of 0.2 m for uncertainty associated with ice sheet flow.Very recent research (Rahmstorf et al. 2007) also suggests that the measured SLRover the last decade was following the upper range SLR projections given in theIPCC Third Assessment Report (TAR) and the IPCC Fourth Assessment Report(AR4) (Note: The upper range TAR projections are very close to the upper rangeAR4 projections when the ice sheet contributions are considered). Furthermore,Rhamstorf (Rahmstorf 2007) suggests that higher SLR rates than those projectedby IPCC TAR and AR4 may also be possible. In comparison, the global averagerate of SLR during the twentieth century was 1–2 mm/year (Church and White 2006;Douglas et al. 2000). This means that the SLR during the twenty-first century couldbe as much as eight times higher than that during the last century, which in turnis likely to result in much faster coastline recession in the twenty-first century. Thesocio-economic impact of such accelerated coastal recession could be massive due tothe unprecedented growth of coastal communities over the last 50 years or so whichhas led to $ billions worth of developments and infrastructure within the coastal zone.To ensure the safety of growing coastal communities and to avoid massive economic