National Snow and Ice Datacenter
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Arctic Sea Ice Extent
Sea level rise contributorsSea level rise contributors
Sea level rise contributors | 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). | | Source: NSIDC | URL: https://nsidc.org/cryosphere/sotc/sea_level.html (The text for the image(s) on this Web page was taken from the above source.) |
Small glacier/ice cap contributionSmall glacier/ice cap contribution
Small glacier/ice cap contribution | Small glacier/ice cap contribution The cumulative contribution to sea level from small glaciers and ice caps (red) plotted with the annual global surface air temperature anomaly (blue). Image courtesy Mark Dyurgerov, Institute of Arctic and Alpine Research, University of Colorado, Boulder. | How glaciers' contribution to sea level is computed
Global mass balance data are transformed to sea-level equivalent by first multiplying the ice thickness (meters) lost to melting by the density of ice (about 900 kilograms per cubic meter), to obtain a water equivalent thickness, and then multiplying by the surface area of these "small" glaciers (about 760,000 square kilometers). This provides an annual average mass balance of approximately -0.273 meters for the period 1961 to 2005. When dividing the mass balance value by the surface area of the oceans (361.6 million square kilometers), the final result is 0.58 millimeters of sea level rise per year. The Glacier Contribution to Sea Level graph demonstrates how the contribution from melting glaciers began increasing at a faster rate starting in the 1990s. This is in agreement with high-latitude air temperature records. The IPCC (2013) stated that it was "very likely" (at least 90 percent confidence) that the mean annual global rate of ocean level increase was 1.5 to 1.9 millimeters between 1901 and 2010, 1.7 to 2.3 millimeters between 1971 and 2010, and 2.8 to 3.6 millimeters between 1993 and 2010. | | Source: NSIDC | URL: https://nsidc.org/cryosphere/sotc/sea_level.html (The text for the image(s) on this Web page was taken from the above source.) |
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