5.5.5 Ocean Mass Change

Global mean sea level will rise if water is added to the ocean from other reservoirs in the climate system. Water storage in the atmosphere is equivalent to only about 35 mm of global mean sea level, and the observed atmospheric storage trend of about 0.04 mm yr^–1 in recent decades (Section 3.4.2.1) is unimportant compared with changes in ice and water stored on land, described in this subsection. Variations in land water storage result from variations in climatic conditions, direct human intervention in the water cycle and human modification of the land surface.

5.5.5.1 Ocean Mass Change Estimated from Salinity Change

Global salinity changes can be caused by changes in the global sea ice volume (which do not influence sea level) and by ocean mass changes (which do). Thus in principle, global salinity changes can be used to estimate the global average sea level change due to fresh water input (Antonov et al., 2002; Munk, 2003; Wadhams and Munk, 2004). However, the accuracy of these estimates depends on the accuracy of the estimates for both sea ice volume (Hilmer and Lemke, 2000; Wadhams and Munk, 2004; see also Section 4.4) and global salinity change (Section 5.2.3). We assess that the error in estimates of ocean mass changes derived from salinity changes and sea ice melt is too large to provide useful constraints on the sea level change budget (Section 5.5.6).