IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability Changes in coastal geomorphology

Sea-level rise over the last 100 to 150 years is probably contributing to coastal erosion in many places, such as the East Coast of the USA, where 75% of the shoreline removed from the influence of spits, tidal inlets and engineering structures is eroding (Leatherman et al., 2000; Daniel, 2001; Zhang et al., 2004) (Table 1.4; see Table SM1.4 for observations of changes in storm surges, flood height and areas, and waves). Over the last century, 67% of the eastern coastline of the UK has retreated landward of the low-water mark (Taylor et al., 2004).

Table 1.4. Changes in coastal processes.

Type of change Observed changes Period Location References 
Shoreline erosion 75% of shoreline, uninfluenced by inlets and structures, is eroding mid-1800s to 2000 East Coast USA  Zhang et al., 2004 
Shoreline retreat, 0.61 m/yr 1855-2002 Louisiana, USA Penland et al., 2005 
Shoreline retreat, 0.94 m/yr 1988-2002     
Beach erosion prevalent due to sea-level rise, mangrove clearance 1960s-1990s Fiji  Mimura and Nunn, 1998 
Beach erosion due to coral bleaching, mangrove clearance, sand mining, structures 1950s-2000 Tropics: SE Asia, Indian Ocean, Australia, Barbados Wong, 2003 
19% of studied shoreline is retreating, in spite of land uplift, due to thawing of permafrost 1950-1995 Manitounuk Strait, Canada Beaulieu and Allard, 2003 
Shoreline erosion, recent acceleration Pre-1990s to present Estuary and Gulf of St. Lawrence, Canada Bernatchez and Dubois, 2004; Forbes et al., 2004 
Increased thermokarst erosion due to climate warming 1970-2000 rela-tive to 1954-1970 Arctic Ocean, Beaufort Sea coasts, Canada Lantuit and Pollard, 2003 
Beach erosion due to dams across the Nile and reduced river floods due to precipitation changes Late 20th century Alexandria, Egypt Frihy et al., 1996 
Coastal erosion 1843-present UK coastline Taylor et al., 2004 
Wetland changes  About 1,700 ha of degraded marshes became open water; non-degraded marshes decreased by 1,200 ha 1938-1989 Chesapeake Bay, USA  Kearney et al., 2002 
Decreases in salt marsh area due to regional sea-level rise and human impacts 1920s-1999 Long Island, NY; Connecticut, USA Hartig et al., 2002; Hartig and Gornitz, 2004 
Salt marshes keep up with sea-level rise with sufficient sediment supply 1880-2000 Normandy, France Haslett et al., 2003 
Landward migration of cordgrass (Spartina alterniflora) due to sea-level rise and excess nitrogen 1995-1999; late 20th century Rhode Island, USA Donnelly and Bertness 2001; Bertness et al., 2002 
Decrease from 12,000 to 4,000 ha, from land reclamation, wave-induced erosion and insufficient sediment  1919-2000 Venice, Italy Day et al., 2005 
Seaward-prograding mudflats replacing sandy beaches, due to increased dredged sediment supply  1897-1999 Queensland coast, Australia Wolanski et al., 2002 
Wetland losses due to sea-level rise, land reclamation, changes in wind/wave energy, tidal dynamics 1850s-1990s Greater Thames Estuary, UK van der Wal and Pye, 2004 
Decreased rates of deltaic wetland progradation due to reduced sediment supply from dam construction 1960s-2003 Yangtze River Delta, Peoples Republic of China Yang et al., 2005 
Coastal vegetation changes Grassy marshes replaced by mangrove due to sea-level rise, water table changes 1940-1994 South-east Florida, USA Ross et al., 2000 
Mangrove encroachment into estuarine wetlands due to changing water levels, increased nutrient load, and salt-marsh compaction during drought 1940s-1990s South-east Australia Saintilan and Williams,1999; Rogers et al., 2006 

In addition to sea-level change, coastal erosion is driven by other natural factors such as wave energy, sediment supply, or local land subsidence (Stive, 2004). In Louisiana, land subsidence has led to high average rates of shoreline retreat (averaging 0.61 m/yr between 1855 and 2002, and increasing to 0.94 m/yr since 1988) (Penland et al., 2005); further erosion occurred after Hurricanes Katrina and Rita in August 2005. These two hurricanes washed away an estimated 562 km2 of coastal wetlands in Louisiana (USGS, 2006). Climate variability also affects shoreline processes, as documented by shoreline displacement in Estonia associated with increasing severe storms and high surge levels, milder winters, and reduced sea-ice cover (Orviku et al., 2003). Significant sections of glacially rebounding coastlines, which normally would be accreting, are nonetheless eroding, as for example along Hudson Bay, Canada (Beaulieu and Allard, 2003). Reduction in sea-ice cover due to milder winters has also exacerbated coastal erosion, as in the Gulf of St. Lawrence (Bernatchez and Dubois, 2004; Forbes et al., 2004). Degradation and melting of permafrost due to climate warming are also contributing to the rapid retreat of Arctic coastlines in many regions, such as the Beaufort and Laptev Sea coasts (Forbes, 2005).

Anthropogenic activities have intensified beach erosion in many parts of the world, including Fiji, Trinidad and parts of tropical Asia (Mimura and Nunn, 1998; Restrepo et al., 2002; Singh and Fouladi, 2003; Wong, 2003). Much of the observed erosion is associated with shoreline development, clearing of mangroves (Thampanya et al., 2006) and mining of beach sand and coral. Sediment starvation due to the construction of large dams upstream also contributes to coastal erosion (Frihy et al., 1996; Chen et al., 2005b; Georgiou et al., 2005; Penland et al., 2005; Syvitski et al., 2005b; Ericson et al., 2006). Pumping of groundwater and subsurface hydrocarbons also enhances land subsidence, thereby exacerbating coastal erosion (Syvitski et al., 2005a).