Sea level rise contributors
Comparison of volume (white), area (grey) and percent contribution to sea level rise (red) by small glaciers and ice caps, and the Greenland and Antarctic Ice Sheets. Image courtesy (Meier et al., 2007). | Current conditions: contribution from melting glaciers
Global sea level is currently rising as a result of both ocean thermal expansion and glacier melt, with each accounting for about half of the observed sea level rise, and each caused by recent increases in global mean temperature. For the period 1961-2003, the observed sea level rise due to thermal expansion was 0.42 millimeters per year and 0.69 millimeters per year due to total glacier melt (small glaciers, ice caps, ice sheets) (IPCC 2007). Between 1993 and 2003, the contribution to sea level rise increased for both sources to 1.60 millimeters per year and 1.19 millimeters per year respectively (IPCC 2007).
Antarctica and Greenland, the world's largest ice sheets, make up the vast majority of the Earth's ice. If these ice sheets melted entirely, sea level would rise by more than 70 meters. However, current estimates indicate that mass balance for the Antarctic ice sheet is in approximate equilibrium and may represent only about 10 percent of the current contribution to sea level rise coming from glaciers. However, some localized areas of the Antarctic have recently shown significant negative balance, e.g., Pine Island and Thwaites Glaciers, and glaciers on the Antarctic Peninsula. There is still much uncertainty about accumulation rates in Antarctica, especially on the East Antarctic Plateau. The Greenland Ice Sheet may be contributing about 30 percent of all glacier melt to rising sea level. Furthermore, recent observations show evidence for increased ice flow rates in some regions of the Greenland Ice Sheet, suggesting that ice dynamics may be a key factor in the response of coastal glaciers and ice sheets to climate change and their role in sea level rise.
In contrast to the polar regions, the network of lower latitude small glaciers and ice caps, although making up only about four percent of the total land ice area or about 760,000 square kilometers, may have provided as much as 60 percent of the total glacier contribution to sea level change since 1990s (Meier et al. 2007). |