Oceans change as a result of the impact of climatic variability on glaciers and ice caps that further contributes to fluctuation sin sea leve. Observational and modelling studies of glaciers and ice caps indicate an average sea level increase of 0.2 to 0.4 mm/yr during the 20th century.
Since the Last Glacial Maximum about 20,000 years ago, sea level has risen by over 120 m at locations far from present and former ice sheets, as a result of loss of mass from these ice sheets. There was a rapid rise between 15,000 and 6,000 years ago at an average rate of 10 mm/yr. Based on geological data, global average sea level may have risen at an average rate of about 0.5 mm/yr over the last 6,000 years and at an average rate of 0.1 to 0.2 mm/yr over the last 3,000 years. Global sea levels are projected to rise by 15 to 95 cm over the next century . This is more than the sea level rise in the previous 3000 years. Even if greenhouse gas emissions are stabilised, sea levels will continue to rise due to such factors as thermal expansion and glacier retreat. (McCarthy et al 2001)