5.5.5.2 Land Ice

During the 20th century, glaciers and ice caps have experienced considerable mass losses, with strong retreats in response to global warming after 1970. For 1961 to 2003, their contribution to sea level is assessed as 0.50 ± 0.18 mm yr^–1 and for 1993 to 2003 as 0.77 ± 0.22 mm yr^–1 (see Section 4.5.2).

As discussed in Section 4.6.2.2 and Table 4.6, the Greenland Ice Sheet has also been losing mass in recent years, contributing 0.05 ± 0.12 mm yr^–1 to sea level rise during 1961 to 2003 and 0.21 ± 0.07 mm yr^–1 during 1993 to 2003. Assessments of contributions to sea level rise from the Antarctic Ice Sheet are less certain, especially before the advent of satellite measurements, and are 0.14 ± 0.41 mm yr^–1 for 1961 to 2003 and 0.21 ± 0.35 mm yr^–1 for 1993 to 2003. Geodetic data on Earth rotation and polar wander allow a late-20th century sea level contribution of up to about 1 mm yr^–1 from land ice (Mitrovica et al., 2006). However, recent estimates of ice sheet mass change exclude the large contribution inferred for Greenland by Mitrovica et al. (2001) from the geographical pattern of sea level change, confirming the lower rates reported above.