Physical and chemical changes in the ocean over basin-wide zones and decadal or longer time-scales: perspectives on current and future conditions - Ocean Sustainability in the 21st Century - page 104

3.8 Sea-level change
Rising sea level has serious implications for the estimated 600 million people who live near
the ocean within 10 m of sea level (Nicholls et al ., 2011 ) . Global mean sea level rose by
1.7 ± 0.2 mm/yr over the period 1900-2009 and has risen by 1.9 ± 0.2 mm/yr since 1961.
Since the start of the satellite altimetry record in 1993, the rate of sea-level rise has been
about 3 mm/yr, with the rate from the satellite record (which covers the open ocean) be-
ing about 0.04 mm/yr higher than the conventional record from coastal and island meas-
urements, corrected for glacial isostatic adjustment (Church and White, 2011 ) . During the
period 1955-1998, thermal expansion (0-3000 m) accounted for about 0.4 mm/yr (Bindoff
et al ., 2007 ) , rising to about 0.8 mm/yr during the period 1972-2008 (Church et al ., 2011 ) .
The contribution from the melting of glaciers and ice caps was about 0.7 mm/yr during this
latter period. For the first time, Church et al . ( 2011 ) have 'closed' the sea-level rise budget:
for the period 1972-2008, the observed sea-level rise from tide gauges and altimeter data
(2.1 ± 0.2 mm/yr) agrees with the sum of the contributions (1.8 ± 0.4 mm/yr).
Church and White ( 2011 ) estimate the global average sea-level rise during the period
1880-2009 to be 201 mm (= 20.1 cm). The 2007 IPCC projection for the 21st century spans
18-59 cm, depending on which scenario is used, but future rapid changes in ice sheet flow
were excluded due to large uncertainty in the projections. For comparison, during the last
warm period at about 125,000 years ago, polar regions were significantly warmer than at
present (~3-5 °C) with an estimated sea level 7-9 m higher than today (Kopp et al ., 2009 ) .
Between the last glacial maximum 24,000 years BP and 4000 years BP, sea level rose ~120
m to the present level (Fig. 6.8 in Jansen et al ., 2007 ).
Recent measurements of ice sheet mass balance changes from satellite-borne gravity
measurement (Shepherd et al ., 2012 ) allow improved projections of sea-level rise during the
21st century. For example, Vermeer and Rahmstorf ( 2009 ) , using semi-empirical methods
relating sea-level rise to temperature rise, estimate for the IPCC 2007 scenarios a sea-level
rise of 75-190 cm for the period 1990-2100. Nicholls et al . ( 2011 ) review projections of