There is no evidence for any acceleration of sea level rise in data from the 20th century data alone. Mediterranean records show decelerations and even decreases in sea level in the latter part of the 20th century.
Most records show evidence of a gradual rise in global mean sea level over the last century. However, signals caused by land movements (e.g. uplift or submergence) can mask this signal due to actual changes in sea level.
The IPCC has estimated that, if the emission of greenhouse gases continues at the current rate, the level of the sea surface will rise by an additional 8-20 cm by 2030, 21-71 cm by 2070 and 31-110 cm by 2100.
Global Sea Level Change Over the Last 140,000 Years (IPCC TAR)
Satellite altimetry provides near-global coverage of the world’s oceans and thus the promise of determining the global-averaged sea level rise, its regional variations, and changes in the rate of rise more accurately and quickly than is possible from the sparse array of in situ gauges.
TOPEX/Poseidon satellite altimeter mission with its (near) global coverage from 66°N to 66°S was launched in August 1992. Estimates of the rates of rise from the short T/P record are 2.5 ± 1.3 mm/ yr over the 6-yr period 1993–98 (Church et al, 2004).
Using a combination of tide gauge records and satellite altimetry, Jevrejeva et al. (2006) have estimated this rate to be 2.4 mm/yr over the same period.
Whether this larger estimate is a result of an increase in the rate of rise, systematic errors in the satellite and/or in situ records, the shortness of the satellite record, or a reflection of the large error bars is not clear.
Analysis of TOPEX/Poseidon satellite altimeter data has demonstrated that meaningful estimates of global averaged mean sea level change can be made over much shorter periods than possible with tide gauges because the global satellite data account for horizontal displacements of ocean mass.
However, achieving the required sub-millimeter accuracy is demanding and requires satellite orbit information, geophysical and environmental corrections and altimeter range measurements of the highest accuracy. It also requires continuous satellite operations over many years and careful control of biases.
