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Indicator Assessment
Past trends
The mass balance of the Greenland ice sheet is determined by snow fall, summer melting of snow, submarine melting at the tongue of marine outlet glaciers, and icebergs breaking off the glaciers. Surface melting occurs when warm air and sunlight first melt all the previous year’s snow and then the ice itself. The changing balance between accumulation on the one hand and melting and calving on the other hand determines the future development of the Greenland ice sheet. Several different methods are used to monitor the changes of the Greenland ice sheet. The overall conclusion of 18 recent studies is that Greenland is losing mass at an accelerating rate (Figure 1). The average ice loss increased from 34 (uncertainty interval: -6 to 74) billion tonnes per year over the period 1992-2001 to 215 (157 to 274) billion tonnes per year over the period 2002-2011 and further to 375 (351 to 399) billion tonnes per year over the period 2011-2013. The average ice loss in the last decade corresponds to a sea-level rise of approximately 0.6 mm per year, which is about a fifth of the total sea-level rise of 3.2 mm per year during this period [i]. Ice is lost from Greenland, in roughly equal amounts, through surface melting and ice motion, and both components have increased [ii].
The area subject to summer melt has increased significantly over recent decades (Figure 2) [iii]. Exceptional melting was recorded on the Greenland ice sheet in the summer of 2012. For a few days in July 2012 nearly the entire ice cover experienced some degree of surface melting. This melt extent was the largest in the satellite era and melting lasted up to 2 months longer than the 1979–2011 mean. Near surface temperature, albedo, exposure of bare ice, surface mass balance and runoff also set new records, as did the total mass balance. The extreme melt event coincided with an unusually strong ridge of warm air over Greenland in the summer of 2012 associated with anomalies in the North Atlantic Oscillation. Ice core data suggest that large-scale melting events of this type have occurred once every few hundred years on average, the most recent ones in 1889 and in the 12th century. It is not currently possible to tell whether the frequency of these rare extensive melt events has changed [iv].
Projections
All recent studies indicate that the mass loss of the Greenland ice sheet, and the associated contribution to global sea-level rise, will be increasingly positive, and that scenarios of greater radiative forcing lead to a larger sea level contribution. Recent studies give an upper bound of about 16 cm sea-level rise from the Greenland ice sheet during the 21st century for a high emission scenario and somewhat lower values for lower emission scenarios [v]. One recent study estimated the Greenland ice sheet contribution until the year 3000 to be 1.4, 2.6 and 4.2 m for the emissions scenarios SRES B1, A1B and A2 (with stabilized greenhouse concentrations after 2100), respectively [vi].
On multi-millennial time scales, the Greenland ice sheet shows threshold behaviour due to different feedback mechanisms. If a temperature above the threshold is maintained for an extended period, the melting of the Greenland ice sheet self-amplifies, which eventually results in near-complete ice loss (equivalent to a sea level rise of about 7 m). Coupled climate-ice sheet models with a fixed topography (that do not consider the feedback between surface mass balance and the height of the ice sheet) estimate the threshold in global mean surface temperature above which the Greenland ice will completely melt to lie between 2°C and 4°C above preindustrial levels [vii]. In contrast, the only study presently available with a dynamical ice sheet suggests that the threshold could be as low as about 1°C above pre-industrial levels. The complete loss of the Greenland ice sheet is not inevitable because it has a long timescale. Complete melting would take tens of millennia near the threshold and a millennium or more for temperatures a few degrees above the threshold [viii].
[i] D. G. Vaughan et al., ‘Observations: Cryosphere’, inClimate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T. F. Stocker et al. (Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press, 2013), Chapter 4, http://www.climatechange2013.org/images/report/WG1AR5_Chapter04_FINAL.pdf; Andrew Shepherd et al., ‘A Reconciled Estimate of Ice-Sheet Mass Balance’,Science 338, no. 6111 (30 November 2012): 1183–89, doi:10.1126/science.1228102; V. Helm, A. Humbert, and H. Miller, ‘Elevation and Elevation Change of Greenland and Antarctica Derived from CryoSat-2’,The Cryosphere 8, no. 4 (20 August 2014): 1539–59, doi:10.5194/tc-8-1539-2014.
[ii] M. van den Broeke et al., ‘Partitioning Recent Greenland Mass Loss’,Science 326, no. 5955 (12 November 2009): 984–86, doi:10.1126/science.1178176; Vaughan et al., ‘Observations: Cryosphere’.
[iii] X. Fettweis et al., ‘Melting Trends over the Greenland Ice Sheet (1958–2009) from Spaceborne Microwave Data and Regional Climate Models’,The Cryosphere 5, no. 2 (2011): 359–75, doi:10.5194/tc-5-359-2011; Vaughan et al., ‘Observations: Cryosphere’.
[iv] S. V. Nghiem et al., ‘The Extreme Melt across the Greenland Ice Sheet in 2012’,Geophysical Research Letters 39, no. 20 (2012): L20502, doi:10.1029/2012GL053611; M. Tedesco et al., ‘Evidence and Analysis of 2012 Greenland Records from Spaceborne Observations, a Regional Climate Model and Reanalysis Data’,The Cryosphere 7, no. 2 (4 April 2013): 615–30, doi:10.5194/tc-7-615-2013.
[v] J. A. Church et al., ‘Sea-Level Change’, inClimate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T. F. Stocker et al. (Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press, 2013), Chapter 13, http://www.climatechange2013.org/images/report/WG1AR5_Chapter13_FINAL.pdf.
[vi] H. Goelzer et al., ‘Millennial Total Sea-Level Commitments Projected with the Earth System Model of Intermediate Complexity LOVECLIM’,Environmental Research Letters 7, no. 4 (1 December 2012): 045401, doi:10.1088/1748-9326/7/4/045401; Church et al., ‘Sea-Level Change’.
[vii] J. G. L. Rae et al., ‘Greenland Ice Sheet Surface Mass Balance: Evaluating Simulations and Making Projections with Regional Climate Models’,The Cryosphere 6, no. 6 (9 November 2012): 1275–94, doi:10.5194/tc-6-1275-2012; X. Fettweis et al., ‘Estimating Greenland Ice Sheet Surface Mass Balance Contribution to Future Sea Level Rise Using the Regional Atmospheric Climate Model MAR’,The Cryosphere 7 (2013): 268–489, doi:10.5194/tc-7-469-2013; Church et al., ‘Sea-Level Change’.
[viii] Alexander Robinson, Reinhard Calov, and Andrey Ganopolski, ‘Multistability and Critical Thresholds of the Greenland Ice Sheet’,Nature Climate Change 2, no. 6 (June 2012): 429–32, doi:10.1038/nclimate1449; Church et al., ‘Sea-Level Change’.
In April 2013 the European Commission presented the EU Adaptation Strategy Package (http://ec.europa.eu/clima/policies/adaptation/what/documentation_en.htm). This package consists of the EU Strategy on adaptation to climate change /* COM/2013/0216 final */ and a number of supporting documents. One of the objectives of the EU Adaptation Strategy is Better informed decision-making, which should occur through Bridging the knowledge gap and Further developing Climate-ADAPT as the ‘one-stop shop’ for adaptation information in Europe. Further objectives include Promoting action by Member States and Climate-proofing EU action: promoting adaptation in key vulnerable sectors. Many EU Member States have already taken action, such as by adopting national adaptation strategies, and several have also prepared action plans on climate change adaptation.
The European Commission and the European Environment Agency have developed the European Climate Adaptation Platform (Climate-ADAPT, http://climate-adapt.eea.europa.eu/) to share knowledge on observed and projected climate change and its impacts on environmental and social systems and on human health; on relevant research; on EU, national and subnational adaptation strategies and plans; and on adaptation case studies.
No targets have been specified.
Estimates are based on the mass budget method based on a combination of the output from regional climate models and various satellite-borne datasets (altimetry and gravimetry data).
The graphs show the data as delivered by the authors of the referenced publications; a linear trend line was added.
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Data on the cryosphere vary significantly with regard to availability and quality. Snow and ice cover have been monitored globally since satellite measurements started in the 1970s. Improvements in technology allow for more detailed observations and higher resolution. Direct historical area-wide data on the Greenland ice sheet tracks about 20 years, but reconstructions give a 200 000 year perspective.
Further information on uncertainties is provided in Section 1.7 of the EEA report on Climate change, impacts, and vulnerability in Europe 2012 (http://www.eea.europa.eu/publications/climate-impacts-and-vulnerability-2012/)
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For references, please go to https://eea.europa.eu./data-and-maps/indicators/greenland-ice-sheet-2/assessment-1 or scan the QR code.
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