Determination and Quantification of the 20th Century Sea Level Rise
Chung-Yen Kuo(1) , C.K. Shum(1) , and Yuchan Yi(2)
Ohio State University,
125 S. Oval Mall,
(2) Ohio state university, 155 S Oval Drive, Columbus, Ohio 43210, United States
Satellite altimetry with a cluster of spaceborne instruments measuring sea surface height changes for over 15 years since the launch of ESA's ERS-1 mission, has been widely accepted to be a viable tool for monitoring contemporary and future global sea level changes. The observational data span extends to about two decades but with 3 year data gap, if one includes US Navy's GEOSAT satellite altimetry data. Sea level rise has been widely recognized as a measurable signal as one of the consequences of possible anthropogenic (human-induced) effect of global climate change. The small rate of sea level rise signal, at 1-2 mm/yr during the last century [IPCC, Church et al., 2001], at present could only be partially explained by a number of competing geophysical processes, each of which is a complex process within the Earthatmosphere-ocean-cryosphere-hydrosphere system. These signals include the mass balance of the ice sheets [Thomas et al., 2004; Krabill et al., 2005], ice shelves, and glaciers [Dyurgerov and Carter, 2004]; retention of water in reservoirs [Sahagian, 2004], terrestrial hydrological balance [Milly et al., 2003; Ngo- Duc et al., 2005], thermosteric [Levitus et al., 2005] and halosteric effects [Boyer et al., 2005] and barotropic response [Ponte, 2005] of the ocean, and other effects. At present, these signals are unable to fully account for about 0.2-1.2 mm/yr of the tide gauge determination of 20th Century sea level rise rate of 1.8 mm/yr [Douglas, 2001, Church et al., 2004, Cazenave et al., 2004; Miller and Douglas, 2004]. Significant geographical variations in both the thermosteric and halosteric sea level [Levitus et al., 2003] and the ''self-gravitational'' sea level signal as result of present-day ice melt [Mitrovica et al., 2001; Plag and Juttner, 2001, Tamisiea et al., 2002], and the effect of glacial isostatic adjustment (GIA) since the last Ice Age causing vertical motions of tide gauge benchmarks [Peltier, 1995, Milne et al., 2001], along with sparseness of world tide gauge locations, all contribute to errors in tide gauge determination of the 20th century sea level rise. The use of multiple satellite altimetry (GEOSAT, ERS-1, TOPEX/POSEIDON, ERS- 2, GFO, JASON and ENVISAT), which has near global coverage (up to ±81.5 deg latitude), however, is limited in data span (1985-2005, ~20 years with 2 year gap) and requires knowledge of instrument drifts, making the determination of sea level trend challenging. This paper provides an updated quantification of the 20th century sea level rise sources using data from multiple satellite altimetry missions spanning ~20 years and ~600 selected long-term tide gauges, accounting for relative biases between the altimeters, modeling effects of steric sea level, vertical motions affecting tide gauge measurements, self gravitations, barotropic ocean response and others. Finally the paper provides an assessment of the contribution of decadal altimetry to the problem of understanding past and future global sea level rise.