Drilling to Decipher Long-Term Sea-Level Changes and Effects—A Joint Consortium for Ocean Leadership, ICDP, IODP, DOSECC, and Chevron Workshop

One of the most societally relevant objectives of the Earth sciences is to understand the history and impact of global sea-level (eustatic) fluctuations at different timescales. Over a third of the world’s population lives within 100 km of a coastline. One-tenth of the global population and thirteen percent of the world’s urban population live in coastal areas that lie within just 10 m above sea level (the Low Elevation Coastal Zone or LECZ), which covers only two percent of the world’s land area (McGranahan et al., 2007). Reconstruction of global mean sea level since 1870 indicates a twentieth century rate of sea-level rise of 1.7 ± 0.3 mm yr−1 and a significant acceleration of sea-level rise of 0.013 ± 0.006 mm yr−2(Church and White, 2006), in part due to anthropogenic influences. Satellite observations in the last decade show that the rates have increased since 1993 to 3.3 ± 0.4 mm yr-1 (Cazenave and Nerem, 2004). Remote-sensing data suggest that ice sheets currently contribute little to sea-level rise. Best estimates are that sea level could rise by as much as 50 cm in the next 100 years (IPCC, 2007). However, dynamical instabilities in response to climate warming may cause faster ice-mass loss (Cazenave, 2006). Rahmstorf et al (2007) showthat sea-level observations are tracking at the high end of the IPCC estimates and conclude that 80 cm, and perhaps >1 m, is the most likely global rise by 2100. In some of the most heavily populated areas (e.g., the U.S. Atlantic seaboard) relative sea-level rise exceeds 4 mm yr-1 (Psuty and Collins, 1996) due to combined effects of global sea-level rise and subsidence. While such rates are gradual on a human timescale, the geological record shows that they can increase rapidly and dramatically (e.g., >2 m in a century; Fairbanks,1989; Bard et al., 1990); in addition, the retreat of shorelines can be erratic and rapid even under conditions of moderate global rises of sea level.

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