Description:
The two main reasons for sea-level rise are thermal expansion of ocean waters as they warm, and increase in the ocean mass, principally from land-based sources of ice (glaciers and ice caps, and the ice sheets of Greenland and Antarctica). Global warming from increasing greenhouse gas concentrations is a significant driver of both contributions to sea-level rise. From 1955 to 1995, ocean thermal expansion is estimated to have contributed about 0.4 mm per year to sealevel rise, less than 25 per cent of the observed rise over the same period. For the 1993 to 2003 decade, when the best data are available, thermal expansion is estimated to be significantly larger, at about 1.6 mm per year for the upper 750 m of the ocean alone, about 50 per cent of the observed sea-level rise of 3.1 mm per year. Kaser and others estimate the melting of glaciers and ice caps (excluding the glaciers surrounding Greenland and Antarctica) contributed to sea-level rise by about 0.3 mm per year from 1961 to 1990 increasing to about 0.8 mm per year from 2001–2004. (uncertainity intervals in the figure are 5 to 95%)