What is the trend in the mass and the melting area of the Greenland ice sheet , and what is the effect on global sea level?

Mass balance of the Greenland ice sheet from mass budget calculations

Note: The figure shows the mass balance of the Greenland ice sheet from mass budget calculations.

Data source:

• Recent mass balance estimates of the Greenland ice sheet provided by Utrecht University (UU)

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Trend in yearly cumulated melting area of the Greenland ice sheet

Note: The figure shows the change in yearly cumulated area of the Greenland ice sheet and it's melt during the period 1979 to 2011 in percentage relative to area in 1979=100. The linear trend 1979–2011 is included.

Data source:

• Annual cumulated melt area of the Greenland ice sheet provided by University of Liège (ULg)

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Past trends

The mass balance of the Greenland ice sheet is determined by snow fall, summer melting of snow, and the icebergs breaking off the glaciers. Several different methods are used to monitor the changes of the Greenland ice sheet [i].  The overall conclusion is that Greenland is losing mass at an accelerating rate (Figure 1). The yearly cumulated area where melting occurs has also increased significantly (Figure 2). Since 2006, high summer melt rates have led to a Greenland ice sheet mass loss of 273 billion tonnes a year [ii]. This ice loss corresponds to a sea-level rise of approximately 0.7 mm per year (about a quarter of the total sea-level rise of 3.1 mm a year). 

Exceptional melting was recorded on the Greenland ice sheet in the summer of 2012. On 12 July 2012 nearly the entire ice cover experienced some degree of surface melting [iii]. The extreme melt event coincided with an unusually strong ridge of warm air over Greenland. The ridge was one of a series that dominated Greenland's weather in the summer of 2012. Ice core data suggest that large-scale melting events of this type have occurred about once every 150 years on average, the most recent one in 1889. It is not currently possible to tell whether the frequency of these rare extensive melt events has changed.

Ice is lost from Greenland, in roughly equal amounts, through surface melting and ice motion [iv]. Surface melting occurs when warm air and sunlight first melt all the previous year’s snow and then the ice itself. At higher elevations snow accumulates and the local mass balance remains positive. With global warming the height at which melting occurs moves upwards and eventually a tipping point may be reached after which the whole ice sheet starts to melt [v].

Projections

Projections of the surface mass balance of the Greenland ice sheet with many global climate models indicate that the ‘tipping point’ above which the Greenland ice decline will completely melt is a global temperature rise of about 3 °C [vi]. However, this estimate is subject to considerable uncertainty [vii].

Climate models with an embedded dynamic ice sheet model have suggested that a melt of 10–20 % of the current ice sheet volume, inducing ice loss in southern Greenland, would lead to an irreversible sea-level rise of about 1.3 m over several centuries. The addition of contributions by outlet glaciers [viii] and the expected surface mass balance-driven losses give an upper bound of about 19 cm sea-level rise from the Greenland ice sheet by 2100.

[i] W.B. Krabill et al., “Aircraft Laser Altimetry Measurement of Elevation Changes of the Greenland Ice Sheet: Technique and Accuracy Assessment,” Journal of Geodynamics 34, no. 3–4 (October 2002): 357–376, doi:10.1016/S0264-3707(02)00040-6; A Shepherd and D Wingham, “Recent Sea-level Contributions of the Antarctic and Greenland Ice Sheets,” Science 315, no. 5818 (2007): 1529–1532, doi:10.1126/science.1136776; H. Jay Zwally et al., “Greenland Ice Sheet Mass Balance: Distribution of Increased Mass Loss with Climate Warming; 2003-07 Versus 1992-2002,” Journal of Glaciology 57, no. 201 (2011): 88–102, doi:10.3189/002214311795306682; J. L. Chen, C. R. Wilson, and B. D. Tapley, “Interannual Variability of Greenland Ice Losses from Satellite Gravimetry,” Journal of Geophysical Research 116 (July 28, 2011): B07406, doi:10.1029/2010JB007789; E. Rignot et al., “Acceleration of the Contribution of the Greenland and Antarctic Ice Sheets to Sea Level Rise,” Geophysical Research Letters 38 (March 4, 2011): L05503, doi:10.1029/2011GL046583.

[ii] Rignot et al., “Acceleration of the Contribution of the Greenland and Antarctic Ice Sheets to Sea Level Rise.”

[iii] NASA, “Satellites See Unprecedented Greenland Ice Sheet Melt,” 2012, http://www.jpl.nasa.gov/news/news.php?release=2012-217.

[iv] M. van den Broeke et al., “Partitioning Recent Greenland Mass Loss,” Science 326, no. 5955 (November 12, 2009): 984–986, doi:10.1126/science.1178176.

[v] J. M Gregory and P. Huybrechts, “Ice-sheet Contributions to Future Sea-level Change,” Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 364, no. 1844 (July 15, 2006): 1709–1732, doi:10.1098/rsta.2006.1796.

[vi] Gregory and Huybrechts, “Ice-sheet Contributions to Future Sea-level Change.”

[vii] Marion Bougamont et al., “Impact of Model Physics on Estimating the Surface Mass Balance of the Greenland Ice Sheet,” Geophysical Research Letters 34 (September 1, 2007): L17501, doi:10.1029/2007GL030700.

[viii] J. K. Ridley et al., “Elimination of the Greenland Ice Sheet in a High CO₂ Climate,” Journal of Climate 18, no. 17 (September 2005): 3409–3427, doi:10.1175/JCLI3482.1; W. T. Pfeffer, J. T. Harper, and S. O’Neel, “Kinematic Constraints on Glacier Contributions to 21st-Century Sea-Level Rise,” Science 321, no. 5894 (September 5, 2008): 1340–1343, doi:10.1126/science.1159099.