The two factors leading to global sea-level rise are thermal expansion due to ocean warming and melting on continental glaciers (melting sea ice has no effect on sea level). Miller and Douglas (2004) report that estimates of volume increase due to global warming give a 0.5 mm/yr contribution to sea level rise. Estimates of the contribution from melting continental ice are less than 0.5 mm. But actual measurements of sea-level rise from tide gauges give a value between 1.5 and 2.0 mm/yr. The analysis of Miller and Douglass (2004) suggests that the tide gauge measurements are accurate and that the contribution from melting ice has been underestimated.
Reference
Miller, L, and B.C. Douglas, 2004: Mass and volume contributions to twentieth-century global sea level rise. Nature, 428, 406-408.