Changes in the Greenland Ice Sheet and Implications for Global Sea Level Rise

Eric Rignot

The Greenland Ice Sheet is changing rapidly in response to climate warming. Even though snowfall slightly increased in the interior, coastal regions are melting and sliding to the sea faster than before, which causes sea level to rise. Between melting, snowfall and faster sliding, the acceleration of glaciers to the sea contributes two-thirds of the mass loss; that is, it dominates the ice sheet response to climate warming. Over the last decade, the mass deficit of the ice sheet doubled, and in 2005 it exceeded 200 cubic kilometers of ice per year (50 cubic miles per year), a rate that would be sufficient to raise sea level by 0.6 mm per year (0.25 inches per year). Because warming will cause more glaciers to speed up and ice will continue to thin further inland, this rate of mass loss will increase as climate continues to warm. Global climate models project roughly 1-2 ft of sea level rise by 2100, but these models do not include a complete description of glacier mechanics and cannot explain current observations. At present, we do not have models capable of predicting the future state of the Greenland Ice Sheet. Other considerations, based on air temperature and paleoclimatic evidence, suggest that sea level could rise by as much as 1-3 m (3-10 ft) by 2100.

Knowing what the ice sheet is doing today and how it will behave in the future is a problem of considerable societal and scientific importance. There is enough ice left in Greenland to raise global sea level by roughly 7 m (about 21 ft). Complete melting of Greenland is unlikely, however, unless enormous warming takes place (Gregory et al, 2004). During the last interglacial about 127,000 years ago, when air temperatures in the region of the Greenland Ice Sheet were only 2-3°C warmer than today, the ice sheet got considerably smaller and likely contributed roughly 3 m (about 10 ft) to global sea level rise (Otto-Bleisner et al, 2006; Overpeck et al 2006).

As recently as the early 1990s, little was known about the balance between the input of snow to the ice sheet versus the discharge of ice into the ocean as icebergs and meltwater, the so-called mass balance of the ice sheet. The situation

Figure 5.1 Ice velocity mosaic of the Greenland Ice Sheet assembled from year 2000 Radarsat-1 interferometry data, color coded on a logarithmic scale from 1 m/yr (brown) to 3 km/yr (purple), overlaid on a map of radar brightness from ERS-1/Radarsat-1/Envisat radar images (see Plate 3 for color version)

Figure 5.1 Ice velocity mosaic of the Greenland Ice Sheet assembled from year 2000 Radarsat-1 interferometry data, color coded on a logarithmic scale from 1 m/yr (brown) to 3 km/yr (purple), overlaid on a map of radar brightness from ERS-1/Radarsat-1/Envisat radar images (see Plate 3 for color version)

Note: Drainage boundaries are shown in red and blue. Kangerdlugssuaq Glacier is 10, Helheim Glacier is 11, southeast Greenland glaciers are 12 and 13, Jakobshavn Isbrae is 20, Rinks Isbrae is 23, northwest Greenland glaciers are 26-31.

has improved considerably over the last decade due to the widespread application of airborne and satellite techniques combined with in-situ data collection. At the same time, major glaciological changes took place in Greenland (see Figure 5.1, Plate 3), most of which were not expected, and challenged prevailing views on the evolution of the ice sheet (Rignot and Kanagaratnam, 2006).

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