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Recent Sea-Level Contributions of the Antarctic and Greenland Ice Sheets

Andrew Shepherd and Duncan Wingham


Totten Animation 3D animation of Antarctica, showing elevation changes in colour (red=30 cm per year thinning; blue=30 cm per year thickening). Also shown in black are the boundaries of four glaciers that are thinning today; the Pine Island and Thwaites glaciers in West Antarctica and the Cook and Totten glaciers in East Antarctica. These glaciers share a common geometry - they are seated in deep submarine basins and flow directly into the ocean - and are vulnerable to future ocean warming. The animation ends at Totten Glacier.


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IPCC Photo 1. Projected global climate warming over the 21st century under a range of emissions scenarios. (Image: IPCC)
Helheim Glacier Photo 2. Perspective view of the Helheim Glacier at different times over the past 3 years. Between 2004 and 2005, the glacier front had retreated 3 miles inland and its ice discharge was accelerating. However, since then it has advanced to a new stable position. This erratic behaviour is a common feature of such tidewater glaciers, and complicates estimates of the ice sheet's sea level contribution. (Image: Ian Howat)
Jakobshavn Isbrae Photo 3. Calving front of the Jakobshavn Isbrae, an outlet glacier of eastern Greenland, in 1985. Satellite studies since the 1990s have reported a progressive retreat of the ice front in tandem with accelerated ice discharge. However, this photo, which predates the satellite record, provides evidence that the glacier front has stodd at a variety of positions in the past. (Image: David Sugden)
Totten Glacier Photo 4. Satellite image of the Totten Glacier in East Antarctica, which holds enough ice to raise global sea levels by over 9 metres. Our assessment confirms that it and 3 other Antarctic glaciers (the Pine Island, Thwaites, and Cook glaciers) are retreating today. These glaciers are all seated in deep submarine basins and flow directly into the oceans, a configuration that is vulnerable to small changes in ocean temperature such as those that occurred over the 20th century, and those predicted for the 21st century. (Image: ESA)

Figures from Article

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Figure 1 Figure 1. Fluctuations in (A) the rate of snow accumulation (SA) of Antarctica and (B) the net surface mass balance (SMB) of Greenland, determined from model reanalyses of meteorological observations expressed as equivalent sea level rise. Also shown are the ranges of published mean accumulation rates determined from glaciological observations (yellow) and climate models (blue).
Figure 2 Figure 2. (A) Rate of elevation change of the Antarctic Ice Sheet, 1992 to 2003, from ERS satellite radar altimetry. Also shown (inset) is the bedrock geometry, highlighting floating (light grey), marine-based (mid-grey)and continental-based (black) sectors. (B) Elevation change of the trunks (flow in excess of 50 metres per year) of the Pine Island [Basin GH in (A)], Thwaites (Basin GH), Totten (Basin C'D), and Cook (Basin DD') glaciers. All the deflating glaciers coincide with marine-based sectors of the ice sheet. An ice-dynamic origin of the thinning of the East Antarctic glaciers has yet to be confirmed by interferometry. However, the correlation of the thinning with flow velocity and the fact that the thinning rate is secular make ice dynamics the likely cause of all Antarctic mass losses.
Figure 3 Figure 3. (A) Rate of elevation change of the Greenland Ice Sheet, 1992 to 2003, determined from satellite gravimetry. Also shown (inset) is the ice surface geometry, highlighting areas above (grey) and below (black) 2000m elevation. Both instruments concur that high elevation areas are growing and low elevation areas are losing mass. According to gravimetry and repeat InSAR measurements of ice discharge, the rate of mass loss at low elevations has increased over the past decade.
Table 1 Table 1. Mass balance (MB) of the East Antarctic (EAIS), West Antarctic (WAIS), Antarctic (AIS), and Greenland (GIS) ice sheets as determined by a range of techniques and studies. Not all studies surveyed all of the ice sheets, and the surveys were conducted over different periods within the time framce 1992 to 2006. For comparison, 360 Gt of ice is equivalent to 1 mm of eustatic sea-level rise.

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