Indicator Assessment

Greenland ice sheet

Indicator Assessment

Prod-ID: IND-97-en

Also known as: CLIM 009

Published 27 Feb 2014 Last modified 11 May 2021

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Topics: Climate change adaptation

This page was archived on 26 Aug 2014 with reason: Other (New version data-and-maps/indicators/greenland-ice-sheet-2/assessment-1 was published)

The Greenland ice sheet is the largest body of ice in the Northern Hemisphere and plays an important role in the global climate system. Melting of the Greenland ice sheet has contributed about one fifth to global sea level rise in the last decade.
The Greenland ice sheet has lost ice during the last two decades at an increasing rate. The average ice loss increased from 34 billion tonnes per year (sea-level equivalent 0.09 mm per year) over the period 1992-2001 to 215 billion tonnes per year (0.59 mm per year) over the period 2002-2011.

Model projections suggest further declines of the Greenland ice sheet in the future but the uncertainties are large. The upper bounds for the sea-level contribution during the 21^st century and the 3^rd millennium (until the year 3000) are 16 cm and 4-5 m, respectively.

Cumulative ice mass loss (and sea level equivalent) from Greenland

Chart

Data sources:

Cumulative ice mass loss (provided by Ian Allison, Lead Author) provided by Intergovernmental Panel on Climate Change (IPCC)

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Trend in yearly cumulated melting area of the Greenland ice sheet

Chart

Data sources:

CLIM009-Greenland-Icesheet-Cumulative-Melt, Fettweis, X., M. Tedesco, M. van den Broeke, and J. Ettema provided by

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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. 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. The extreme melt event coincided with an unusually strong ridge of warm air over Greenland in the summer of 2012. 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 12^th century [iv]. It is not currently possible to tell whether the frequency of these rare extensive melt events has changed.

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 21^st 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,” in Climate Change 2013: The Physical Science Basis., ed. T. F. Stocker et al. (Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press, 2013), Chapter 4, http://www.climatechange2013.org/report/full-report/; Andrew Shepherd et al., “A Reconciled Estimate of Ice-Sheet Mass Balance,” Science 338, no. 6111 (November 30, 2012): 1183–1189, doi:10.1126/science.1228102.

[ii] 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; 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): 359–375, 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.

[v] J. A. Church et al., “Sea-Level Change,” in Climate 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/report/full-report/.

[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 (December 1, 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 (November 9, 2012): 1275–1294, 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): 429–432, doi:10.1038/nclimate1449; Church et al., “Sea-Level Change.”

Supporting information

Indicator definition

Cumulative ice mass loss and sea-level equivalent from Greenland

Yearly cumulated melt area of Greenland ice sheet

Units

Gigatonnes and mm sea-level equivalent

% change in melt area

Rationale

Justification for indicator selection

The fate of the Greenland ice sheet highlights potentially major consequences of climate change as it is directly linked to global sea-level rise. The speed of ice loss, known as the ice sheet ‘mass balance’, is the most important indicator of ice sheet change. An increased rate of mass loss results in a faster rise in sea level. In addition, melt water from Greenland reduces the salinity of the surrounding ocean. An upper layer of fresher water may reduce the formation of dense deep water, one of the mechanisms driving global ocean circulation.

Scientific references

IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.
Snow, Water, Ice and Permafrost in the Arctic (SWIPA): Climate Change and the Cryosphere AMAP (2011) Snow, Water, Ice and Permafrost in the Arctic (SWIPA): Climate Change and the Cryosphere. Arctic Monitoring and Assessment Programme (AMAP), Oslo.

Policy context and targets

Context description

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.

Targets

No targets have been specified.

Methodology

Methodology for indicator calculation

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.

Methodology for gap filling

Not applicable

Methodology references

Ice Sheets and Sea Level: Thinking Outside the Box van den Broeke, M. (2011) Ice Sheets and Sea Level: Thinking Outside the Box. Surveys in Geophysics. doi:10.1007/s10712-011-9137-z
Melting trends over the Greenland ice sheet (1958–2009) from spaceborne microwave data and regional climate models Fettweis, X., Tedesco, M., van den Broeke, M. and Ettema, J. (2011) Melting trends over the Greenland ice sheet (1958–2009) from spaceborne microwave data and regional climate models. The Cryosphere 5(2), 359–375. doi:10.5194/tc-5-359-2011

Uncertainties

Methodology uncertainty

Not applicable

Data sets uncertainty

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/)