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Greenland Ice Sheet

M. Tedesco1,2, J. E. Box3, J. Cappelen4, X. Fettweis5, T. Mote6,
R. S. W. van de Wal7, C. J. P. P. Smeets7, J. Wahr8

1City College of New York, New York, NY, USA
2National Science Foundation, Arlington, VA, USA
3Geological Survey of Denmark and Greenland, Copenhagen, Denmark
4Danish Meteorological Institute, Copenhagen, Denmark
5University of Liege, Liege, Belgium
6Department of Geography, University of Georgia, Athens, Georgia, USA
7Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, The Netherlands
8Department of Physics and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA

December 2, 2014

Highlights

  • Melt extent, above the 1981-2010 average for 90% of summer 2014, reached a maximum of 39.3% of the ice sheet area on 17 June 2014. The number of days of melting in June and July 2014 exceeded the 1981-2010 average over most of the ice sheet.
  • Average surface mass balance (the difference between annual snow accumulation and annual melting) measured along the K-transect in west Greenland for the period 2013-2014 was slightly below the 1990-2010 average, while the equilibrium line altitude (~1,730 m a.s.l., the lowest altitude at which winter snow survived) was at a higher elevation than the 1990-2010 average of 1,545 m.
  • A negligible ice mass loss of 6 Gt between June 2013 and June 2014, in contrast to the largest annual loss (474 Gt) observed in the GRACE record in 2012, indicates a slowing of the rate of ice loss.
  • Average albedo during summer 2014 was the second lowest in the period of record that began in 2000; a new record low albedo occurred in August 2014.
  • Summer 2014 in Greenland was the warmest on record at Kangerlussuaq, west Greenland, where the average June temperature was 2.3°C above the 1981-2010 average. In January 2014, the average temperature at Illoqqortoormiut, east Greenland and Upernavik, west Greenland were 7.5°C and 8.7°C above the 1981-2010 means, respectively.

With an area of 1.71 million km2 and volume of 2.85 km3, the Greenland ice sheet is the second largest glacial ice mass on Earth. Only the Antarctic ice sheet is larger. The freshwater stored in the Greenland ice sheet has a sea level equivalent of +7.4 m. The discharge of the ice to the ocean my melting and runoff, and iceberg calving would not only increase sea level, but also likely alter the ocean thermohaline circulation and global climate. The high albedo (reflectivity) of the ice sheet surface (together with that of snow-covered and bare sea ice, and snow on land) plays an important role in the regional surface energy balance and the regulation of global air temperatures.

Surface Melting

Estimates of the spatial extent of melting across the Greenland ice sheet (Fig. 3.1), derived from brightness temperatures measured by the Special Sensor Microwave Imager/Sounder (SSMI/S) passive microwave radiometer (e.g., Mote 2007, Tedesco et al. 2013a, 2013b), show that melt extent for the period June through August (JJA, hereafter referred to as the summer) 2014 was above the 1981-2010 average 90% of the time (83 of 92 days, Fig. 3.1d). Melting occurred over 4.3% more of the ice sheet, on average, than in summer 2013, but 12.8% less than the exceptional summer of 2012 (Fig. 3.1d). Melt extent exceeded two standard deviations above average, reaching a maximum of 39.3% of the total ice sheet area on 17 June (Fig. 3.1b). Similar values occurred on 9 July and 26 July (Fig. 3.1c). Melt extent exceeded the 1981-2010 average on 28 days in June, 25 days in July, and 20 days in August 2014. For a brief period in early August there was below average melt extent, but by 21 August melting areas covered 29.3% of the ice sheet; this exceeded the 1981-2010 average by two standard deviations.

Figure - Melting on the Greenland Ice Sheet in 2014 by total number of days Figure - Melting on the Greenland Ice Sheet in 2014 in June and July
Figure - Melting on the Greenland Ice Sheet in 2014 in melt extent
Fig. 3.1. Melting on the Greenland Ice Sheet in 2014 as described by (a, top left) total number of days when melting was detected at the surface between 1 January and 1 October, 2014; (b, top center) June melt anomaly expressed as the number of days melting that month compared to the 1981-2010 average; (c, top right) July melt anomaly expressed as the number of days melting that month compared to the 1981-2010 average; and (d, bottom) the annual cycle of melt extent expressed as a fraction of the total ice sheet area where melting was detected. In (d), melt extent in 2014 is represented by the blue line and the long-term average is the black line. Black star in (a, top left) indicates the position of the K-transect (discussed in the surface mass balance section).

The number of days of surface melting in June and July 2014 exceeded the 1981-2010 average across most of the ice sheet (Figs. 3.1b and 3.1c), particularly on the western margin, consistent with the above normal temperatures recorded at coastal stations in western Greenland in June and July. Locations with below average days of melting were evident in southeast Greenland (Figs. 3.1b and 3.1c), consistent with below normal temperatures in that region (see Fig. 1.3d in the essay on Air Temperature, which shows lower temperatures in southeast Greenland than along the western margin of the ice sheet).

Surface Mass Balance

Average surface mass balance (the difference between annual snow accumulation and annual melting) measured along the K-transect in West Greenland (Van de Wal et al. 2005, 2012) for the period 2013-2014 was slightly below the mean for 1990-2010 (measurements began in 1990; thus it is not possible to use the standard 1981-2010 reference period) (Fig. 3.2a). The equilibrium line altitude (the lowest altitude at which winter snow survives), estimated to be 1,730 m above sea level [a.s.l.] in 2014, was at a higher elevation than the 1990-2010 mean (1,545 m). During summer 2014, melt rates below the equilibrium line were not as high as they were in some recent years, e.g., 2010 and 2012.

Figure - Surface mass balance as a function of elevation along the K-transect
Figure - Average surface mass balance
Fig. 3.2. (a, top) Surface mass balance as a function of elevation along the K-transect for 2013-2014 (large blue squares), the previous four years, and the 20-year (1990-2010) average. (b, bottom) Average surface mass balance for sites located between 400 m and 1500 m a.s.l. A linear regression (red line) of the data gives a correlation coefficient (r) of 0.46 (significant at a 97.5% confidence level).

Figure 3.2a shows the mass balance profiles for the last five years and the long-term mean obtained from stations at different elevations. Figure 3.2b shows the average surface mass balance for sites between 400 m and 1500 m a.s.l altitude, and the corresponding linear trend. There was slightly more melt in 2013-2014 than the 1990-2010 average; 2013-2014 had the 7th most negative mass balance of the 24 consecutive mass balance years in the observational record. The trend in the mean mass balance over the ablation area is -3.3 cm per year.

Total Ice Mass

GRACE (Gravity Recovery and Climate Experiment) satellite gravity solutions are used to estimate monthly changes in the total mass of the Greenland ice sheet (Velicogna and Wahr 2006; Fig. 3.3). Between the beginning of June 2013 and the beginning of June 2014, which corresponds closely to the period between the onsets of the 2013 and 2014 melt seasons, there was virtually no net change in cumulative ice sheet mass. The very small 6 Gt (Gigatonne) loss during that 12 month period, just 2% of the mass loss of 294 Gt between 2003 and 2013, indicates a slowing in the rate of ice mass loss. The negligible June 2013 to June 2014 mass loss follows a 474 Gt mass loss between June 2012 and June 2013, the largest annual loss observed in the GRACE record. A GRACE mass estimate cannot be obtained for July 2014, because the GRACE K-Band ranging system was switched off during that month to preserve battery life.

Figure - Monthly mass anomalies for the Greenland ice sheet
Fig. 3.3. Monthly mass anomalies (in Gigatonnes, Gt) for the Greenland ice sheet since April 2002 estimated from GRACE measurements. The anomalies are expressed as departures from the 2002-2014 mean value for each month. For reference, orange asterisks denote June values (or May for those years when June is missing).

Ice Albedo

Albedo, also referred to as reflectivity, is the ratio of reflected solar radiation to total incoming solar radiation. Here it is derived from the Moderate-resolution Imaging Spectroradiometer (MODIS, after Box et al. 2012). In summer 2014, albedo was below average over most of the ice sheet (Fig. 3.4a) and the area-averaged albedo for the entire ice sheet was the second lowest in the period of record that began in 2000 (Fig. 3.4b). The area-averaged albedo in August was the lowest on record for that month (Fig. 3.4c). August 2014 albedo values were particularly low at high elevations; such low values have not previously been observed so late in the summer. The observed albedo in summer 2014 continues a period of increasingly negative and record low albedo anomaly values (Box et al. 2012, Tedesco et al. 2011, 2013a, Dumont et al. 2014).

Figure - Greenland ice sheet surface albedo anomaly

Average surface albedo of the ice sheet each summer Average surface albedo of the ice sheet each August
Fig. 3.4. (a, top) Greenland ice sheet surface albedo anomaly for June, July and August (JJA, summer) 2014 relative to the average for those months between 2000 and 2011. (b, lower left) Average surface albedo of the ice sheet each summer between 2000 and 2014. (c, lower right) Average surface albedo of the ice sheet each August between 2000 and 2014. All data are derived from the Moderate-resolution Imaging Spectroradiometer (MODIS).

Weather

Slightly negative (-0.7) North Atlantic Oscillation (NAO) conditions in summer 2014 promoted abnormal anticyclonic conditions over southwest and northwest Greenland; these favored northward advection of warm air along its western margin as far as the northern regions of the ice sheet (see Fig. 1.3d in the essay on Air Temperature). Further, the anticyclonic conditions reduced summer precipitation (snowfall) over south Greenland. The combination of southerly air flow and lower precipitation contributed to the melting, mass balance and albedo observations reported above.

The advection of warm air towards Greenland is reflected in summer air temperatures. Near surface air temperature data recorded by automatic weather stations (Table 3.1) indicate that summer 2014 in Greenland was the warmest on record at Kangerlussuaq, west Greenland, with June temperatures +2.3°C above the 1981-2010 average. Other west Greenland locations also had anomalously warm summer temperatures. For example, the coastal site of Nuuk had its second warmest summer since 1784, with July temperatures 2.9°C above the 1981-2010 mean.

Warming in winter is greater than in summer (Table 3.1). At Ittoqqortoormiut, east Greenland, where observations began in 1924, the average air temperature during December 2013 to February 2014 equalled the record high set in the same period in 1947, and January temperatures were 7.5°C above the 1981-2010 average. Upernavik, west Greenland, had its 7th warmest January, 8.7°C above the 1981-2010 average, since observations began in 1873.

Table 3.1. Near-surface temperature anomalies relative to the 1981-2010 average at thirteen stations distributed around Greenland. Standard deviation (SD) values, and the years when record maximum and minimum values occurred are also given. Data are from Cappelen (2014) and from the Danish Meteorological Institute (DMI) for the period January-August 2014.
Location First year
of record
2014 Anomaly (°C)
St. Deviation (SD)
Max. and Min. Year
SON DJF MAM JJA June July Aug.
      2013 2013 -2014 2014 2014 2014 2014 2014
Pituffik/
Thule AFB
1948 Anomaly (1981-2010) -0.1 +2.4 +0.8 +0.3 +0.3 -0.2 +0.8
Latitude 76.5°N
Longitude 68.8°W
  SD 0.1 0.8 0.3 0.3 0.5 -0.0 0.4
Max. Year 2010 1986 1953 1957 2008 2011 2009
Min. Year 1964 1949 1992 1996 1986 1972 1996
Upernavik 1873 Anomaly (1981-2010) -0.4 +4.7 +0.5 +0.6 +1.3 0.0 +0.4
72.8°N
56.2°W
  SD -0.1 1.3 0.1 1.1 1.5 0.5 0.6
Max. Year 2010 1947 1932 2012 2008 2011 1960
Min. Year 1917 1983 1896 1922 1894 1916 1873
Kangerlussuaq 1949 Anomaly (1981-2010) +0.6 +2.1 -0.9 +1.6 +2.3 +1.6 1.0
67.0°N
50.7°W
  SD 0.4 0.4 -0.3 1.7 1.5 1.4 0.7
Max. Year 2010 1986 2005 2014 2014 1968 1960
Min. Year 1982 1983 1993 1983 1978 1973 1983
Ilulissat 1873 Anomaly (1981-2010) -0.4 +3.5 +0.1 +0.6 +1.4 +0.5 +0.1
69.2°N
51.1°W
  SD -0.1 1.1 -0.0 1.3 1.4 0.8 0.5
Max. Year 2010 1929 1932 1960 1997 1960 1960
Min. Year 1884 1884 1887 1972 1918 1972 1884
Aasiaat 1951 Anomaly (1981-2010) +0.3 +3.9 +1.2 +1.6 +2.2 +1.3 +1.2
68.7°N
52.8°W
  SD 0.4 0.9 0.4 1.5 1.7 1.1 1.0
Max. Year 2010 2010 2010 2012 2012 2012 1960
Min. Year 1986 1984 1993 1972 1992 1972 1983
Nuuk 1873 Anomaly (1981-2010) +0.4 +0.6 -0.9 +2.3 +1.9 +2.9 +2.1
64.2°N
51.8°W
  SD 0.6 0.3 -0.8 2.3 1.4 2.6 1.8
Max. Year 2010 2010 1932 2012 2012 2012 2010
Min. Year 1898 1984 1993 1914 1922 1955 1884
Paamiut 1958 Anomaly (1981-2010) +0.9 +0.8 -1.1 +0.7 +0.5 +0.8 +0.9
62.0°N
49.7°W
  SD 0.8 0.1 -0.7 0.8 0.6 0.7 0.8
Max. Year 2010 2010 2005 2010 1987 1958 2010
Min. Year 1982 1984 1993 1969 1972 1969 1969
Narsarsuaq 1961 Anomaly (1981-2010) +0.8 +0.9 +0.5 +1.0 +1.4 +0.6 +0.9
61.2°N
45.4°W
  SD 0.6 0.1 0.1 1.3 1.3 0.7 0.9
Max. Year 2010 2010 2010 2012 2012 2012 1987
Min. Year 1963 1984 1989 1983 1992 1969 1983
Quaqortoq 1873 Anomaly (1981-2010) +0.5 +0.3 -0.4 +0.6 +0.8 +0.2 +0.8
60.7°N
46.0°W
  SD 0.9 0.3 -0.4 0.7 0.5 0.4 0.8
Max. Year 2010 2010 1932 1929 1929 2012 1960
Min. Year 1874 1884 1989 1874 1922 1969 1874
Danmarkshavn 1949 Anomaly (1981-2010) +0.9 +3.9 +0.4 +0.8 +0.3 +1.0 +1.1
76.8°N
18.8°W
  SD 0.8 2.1 0.4 1.3 0.3 1.3 1.2
Max. Year 2002 2005 1976 2008 2008 1958 2003
Min. Year 1971 1967 1966 1955 2006 1955 1992
Ittoqqortoormiut 1948 Anomaly (1981-2010) +0.3 +5.3 +1.3 0.0 +0.4    
70.4°N
22.0°W
  SD 0.6 2.4 1.1 0.0 0.9    
Max. Year 2002 2014 1996 1949 1948 1949 1949
Min. Year 1951 1966 1956 1955 1956 1953 1952
Tasiilaq 1895 Anomaly (1981-2010) -0.4 +3.0 0.0 +0.6 +0.7 -0.3 +1.2
65.6°N
37.6°W
  SD -0.1 1.7 0.0 0.5 0.3 -0.6 1.5
Max. Year 1941 1929 1929 2003 1932 1929 2003
Min. Year 1917 1918 1899 1983 2012 1983 1983
Prins Christian Sund 1951 Anomaly (1981-2010)     +0.5 +1.2 +1.1 +0.9 +1.6
60.0°N
43.2°W
  SD     0.6 1.6 1.3 1.0 1.7
Max. Year     2005 2010 2008 2005 2010
Min. Year     1989 1970 1993 1969 1992
Note: The more positive or more negative the standard deviation (SD) value, the more extreme the positive or negative temperature anomaly. For example, at Ittoqqortoormiut, where winter 2014 was as warm as the previous warmest winter on record, in 1947, the SD value (2.4) of the winter 2014 temperature anomaly is among the most positive in the table.
Abbreviations: SON: September, October, November; DJF: December, January, February; MAM: March, April, May; JJA: June, July, August.

References

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Cappelen, J. (ed.), 2014: Greenland - DMI Historical Climate Data Collection 1784-2013, Denmark, The Faroe Islands and Greenland. Danish Meteorol. Inst. Tech. Rep., 14-04, 90 pp. http://www.dmi.dk/fileadmin/user_upload/Rapporter/TR/2014/tr14-04.pdf.

Dumont, M., E. Brun, G. Picard, M. Michou, Q. Libois, J. R. Petit, M. Geyer, S. Morin, and B. Josse, 2014: Contribution of light-absorbing impurities in snow to Greenland's darkening since 200. Nature Geoscience, 7, 509-512, doi:10.1038/ngeo2180.

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Tedesco, M., J. E. Box, J. Cappelen, X. Fettweis, T. Jensen, T. Mote, A. K. Rennermalm, L. C. Smith, R. S. W. van de Wal, and J. Wahr. 2013b: [Arctic] Greenland ice sheet [in "State of the Climate in 2012"]. Bull. Amer. Meteor. Soc., 94 (8), S121-S123.

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Van de Wal, R. S. W., W. Boot, C. J. P. P. Smeets, H. Snellen, M. R. van den Broeke, and J. Oerlemans, 2012; Twenty-one years of mass balance observations along the K-transect, West-Greenland. Earth Syst. Sci. Data, 4, 31-35, doi:10.5194/essd-4-31-2012.

Velicogna, I. and J. Wahr. 2006: Significant acceleration of Greenland ice mass loss in spring, 2004: Nature, 443, doi:10.1038/nature05168.