Climate Change And Globalrelative Sealevel Rise

The impacts and responses of coasts to sea-level rise are a product of relative (or local) sea-level rise rather than global changes alone. Relative sea-level rise takes into account global-mean sea-level rise, regional trends in the absolute elevation of the ocean surface, and geological uplift or subsidence and related processes which change the position of the land/sea boundary. Relative sea-level rise is only partly a response to climate change and can vary significantly among coastal systems (Fig. 3). Abrupt changes may occur, for example, where an earthquake causes rapid vertical displacement of a part

1900 1920 1940 1960 1980 2000

FIGURE 3 Selected relative sea level records for the twentieth century, illustrating different types of trend. The records are offset for display purposes. Source: http://www.pol.ac.uk/psmsl/.

-Nezugaseki, Japan - Abrupt change, earthquake (instantaneous rise of 22cm in 1964)

— Bangkok, Thailand - Accelerated rise, increasing human induced subsidence (post 1960 - 17.5mm/yr)

-Grand Isle, USA - Rapid rise, natural deltaic plain subsidence (6.9mm/yr)

-Helsinki, Finland - Falling trend, natural land uplift exceeds global-mean rise (-2.5mm/yr)

-Sydney, Australia - Gradual rise

1900 1920 1940 1960 1980 2000

FIGURE 3 Selected relative sea level records for the twentieth century, illustrating different types of trend. The records are offset for display purposes. Source: http://www.pol.ac.uk/psmsl/.

(adapted from Ref. [23]). Subsidence in Los Angeles was very localised (about 1 km2) and due to oil extraction. Dhaka and Kolkata are thought to be subsiding, but data is limited.

of the Earth's surface (see Nezugaseki; Fig. 3). Sea level is presently falling due to ongoing glacial isostatic adjustment (rebound) in some high-latitude locations that were formerly sites of large (kilometre-thick) glaciers, such as Hudson Bay and the northern Baltic (see Helsinki, Fig. 3). In contrast, sea level is rising more rapidly than global-mean trends on subsiding coasts, including deltas such as the Mississippi delta (see Grand Isle, Fig. 3), the Nile delta, and the large deltas of south and east Asia [20,21]. Most dramatically, human-induced subsidence of susceptible areas due to drainage of organic soils and withdrawal of groundwater can produce dramatic rises in relative sea level, especially in susceptible coastal areas and cities built on recently-deposited deltaic landforms [22]. Four noteworthy examples over the twentieth century are parts of Tokyo and Osaka which subsided up to 5 and 3 m, respectively, most of Shanghai which subsided up to 3 m, and nearly all of Bangkok which subsided up to 2 m (see Bangkok; Figs. 3 and 4). As a management response to human-induced subsidence, stopping shallow sub-surface fluid withdrawals can reduce subsidence.

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