Greenland

J. E. Box¹, L.-S. Bai¹, R. Benson¹, I. Bhattacharya¹, D. H. Bromwich¹, J. Cappelen², D. Decker¹, N. DiGirolamo³, X. Fettweis⁴, D. Hall⁵, E. Hanna⁶, T. Mote⁷, M. Tedesco⁸, R. van de Wal⁹, and M. van den Broeke⁹

¹Byrd Polar Research Center, The Ohio State University, Columbus, Ohio
²Danish Meteorological Institute, Copenhagen, Denmark
³Science Systems Applications Inc. and NASA Goddard Space Flight Center, Greenbelt, Maryland
⁴Department of Geography, University of Liège, Liège, Belgium
⁵NASA Goddard Space Flight Center, Greenbelt, Maryland
⁶Department of Geography, University of Sheffield, England
⁷Department of Geography, University of Georgia, Atlanta, Georgia
⁸Department of Earth and Atmospheric Sciences, City College of New York, New York, New York
⁹Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, The Netherlands

October 19, 2009

Summary

An abnormally cold winter across the southern half of Greenland led to substantially higher west coast sea ice thickness and concentration. Even so, record-setting summer temperatures around Greenland, combined with an intense melt season (particularly across the northern ice sheet), led the 2008 Greenland climate to be marked by continued ice sheet mass deficit and marine-terminating ice disintegration.

Regional surface temperatures

Temperature anomalies were mixed and exhibited seasonal variability (Fig. 5.17). Annual mean temperatures for the whole ice sheet were +0.9°C, but were not abnormal, given a rank of 23 of 51 years over the 1958-2008 period (Box et al. 2006). Persistent warm anomalies were evident over the northern ice sheet in all seasons. Temperatures were abnormally cold over the southern ice sheet in winter. Coastal meteorological stations around Greenland with a consistent 51-yr period (1958-2008) (Cappelen 2009) indicate a record-setting warm summer in 2008. The Upernavik (Nuuk) summer temperature was the warmest (second warmest) on record since 1873, respectively.

Figure G1. (a) winter and (b) summer near-surface (2 m) air temperature anomalies with respect to the 1971–2000 base period, simulated by Polar MM5 after Box et al. (2006). (Click each image for larger version)

Table G1. 2008 Summer 700-hPa temperature and winter precipitation anomalies (relative to 1948–2008 NCEP reanalysis means) for glaciated regions of the Arctic (excluding Greenland). Inferred sign of surface mass balance is based on comparison of historical mass balance records for each region with NCECEP reanalysis temperature and precipitation anomalies. Anomalies in melt duration and the timing of melt onset and freeze-up (relative to 2000–04 climatology) derived from QuikSCAT data. For timing, negative anomalies indicate an earlier-than-normal date.

Upper-air temperatures

Upper-air sounding data available from the Integrated Global Radiosonde Archive (Durre et al. 2006) indicate a continued pattern of lower tropospheric warming and lower stratospheric cooling 1964-onward (Box and Cohen 2006). Lower tropospheric warm anomalies in all seasons, particularly in spring along western Greenland, were accompanied by relatively small midtropospheric cool anomalies. Winter tropopause temperatures (200 hPa) were above normal. Lower stratospheric (above 100 hPa) temperatures were lower than normal.

Surface melt extent and duration

Passive (SMMR and SSM/I, 1979–2008) and active (QuikSCAT, 2000–08) microwave remote sensing (Bhattacharya et al. 2009, submitted to Geophys. Res. Lett.; Liu et al. 2005) indicate abnormally high melt duration over the north and northeast ice sheet and along the east and west coasts above Greenland’s most productive three outlet glaciers in terms of ice discharge into the sea: Kangerlussuaq; Helheim; and Jakobshavn (Fig.G2). Lower-than-normal melt duration is evident over much of the upper elevations of the ice sheet. New records of the number of melting days were observed over the northern ice sheet, where melting lasted up to 18 days longer than previous maximum values. Anomalies near the west coast are characterized by melting up to 5–10 days longer than the average (Tedesco et al. 2008).

Figure G2. 2008 Greenland ice sheet surface melt duration anomalies relative to the 1989–2008 base period based on (a) SSM/I and (b) QuikSCAT (2000–08 base period), after Bhattacharya et al. (2009, submitted to Geophys. Res. Lett.). (Click each image for larger version)

The average daily melt extent, after Mote and Anderson (1995) and Mote (2007), for 2008 was 424,000 km², about 2.4% greater than the 1989–2008 average of 414,000 km², representing the lowest average melt extent since 2001. Significantly more melt occurred in 2008 in the northeast (45.6% greater than the 1989–2008 average) and northwest (29.7%), but less occurred in the two east-central regions (−16.8% and −25.4%) and in the southeast (−21.1%). Melt extent in 2008 was also above the 1979–2007 average. The trend in the total area of melt during 1979–2008 is approximately +15,900 km² yr⁻¹ and is significant at the 95% confidence interval (p < 0.01).

Precipitation anomalies

Annual PT anomalies in 2008, determined using Polar MM5 data assimilation modeling (Bromwich et al. 2001; Cassano et al. 2001; Box et al. 2006), were positive (negative) up to 750 mm (−250 mm) over the eastern (western) ice sheet, respectively. More PT than normal occurred in isolated areas in extreme southeast, east, north, and northwestern Greenland. The overall anomaly indicated approximately 41 Gt more PT than normal for the 1971–2000 standard normal period.

Surface albedo

Melt season (day 92–274) surface albedo anomalies, derived using the Liang et al. (2005) algorithm applied to daily cloud-free MODIS imagery, indicate a lower surface albedo around the ablation zone (except the east ice sheet) (Fig. G3) resulting from the combined effect of the positive summer surface melt intensity anomaly and, in most areas, less winter snow coverage. A positive albedo anomaly is evident for the ice sheet accumulation zone and is consistent with above-average solid precipitation and/or less-than-normal melting/snow grain metamorphism.

Figure G3. Surface albedo anomaly Jun–Jul 2008 relative to a Jun–Jul 2000–08 base period. (Click image for larger version)		Figure G4. 2008 surface mass balance anomalies with respect to the 1971–2000 base period, simulated by Polar MM5 after Box et al. (2006). (Click image for larger version)

Surface mass balance

Polar MM5 climate data assimilation model runs spanning 51 years (1958–2008), calibrated by independent in situ ice-core observations (Bales et al. 2001; Mosley-Thompson et al. 2001; Hanna et al. 2006) and ablation stakes (van de Wal et al. 2006), indicate that 2008 total precipitation and net snow accumulation was slightly (6%–8%) above normal (Table G2). In accordance with a +0.9°C 2008 annual mean surface temperature anomaly, the fraction of precipitation that fell as rain instead of snow, surface meltwater production, and meltwater runoff were 142%–186% of the 1971–2000 mean. Consequently, and despite 6%–9% (39–50 Gt) more snow accumulation than normal, the surface net mass balance was substantially (145 Gt) below normal. 2008 surface mass balance ranked ninth-least positive out of 51 years (1958–2008).

Table G2. Greenland ice sheet surface mass balance parameters: 2008 departures from 1971–2000 average (adapted from Box et al. 2006). Estimates by Hanna et al. (2008) are included for comparison.

Surface mass balance anomalies indicate a pattern of increased marginal melting with noteworthy departures in excess of 1-m water equivalence per year from normal across the northern ice sheet (Fig.G4). The pattern of steepening mass balance profile is consistent with observations from satellite altimetry (Zwally et al. 2005) and airborne altimetry (Krabill et al. 2000); satellite gravity retrievals (e.g., Luthcke et al. 2006); and climate projections (Solomon et al. 2007).

Marine-terminating glacier area changes

Daily surveys of Greenland ice sheet marine terminating outlet glaciers from cloud-free MODIS imagery (http://bprc.osu.edu/MODIS/) indicate that the 34 widest glaciers collectively lost 106.4 km² of marine-terminating ice between the end of summer 2008 and the end of summer 2009 (Figure G4). This is equivalent to an area 20% larger than Manhattan Island (87.5 km²), New York. The largest individual glacier losses are observed at: Humboldt (-37 km²); Zachariae Isstrom (-31 km²); and Midgard (-16 km²). The 2000-2009 rate (106 km²) has been linear (R = −0.98) despite the fact that a few individual glaciers exhibit erratic annual net ice area changes. The cumulative area change from end-of-summer 2000 to 2009 is −990 km², an area 11.3 times that of Manhattan Island.

Figure G4. Cumulative annual area changes for 34 of the widest Greenland ice sheet marine-terminating outlets.

References

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Box, J. E., and A. E. Cohen, 2006: Upper-air temperatures around Greenland: 1964–2005. Geophys. Res. Lett., 33, L12706, doi:10.1029/2006GL025723.

Bromwich, D., J. Cassano, T. Klein, G. Heinemann, K. Hines, K. Steffen, and J. E. Box, 2001: Mesoscale modeling of katabatic winds over Greenland with the Polar MM5. Mon. Wea. Rev., 129, 2290–2309.

—, and Coauthors, 2006: Greenland ice sheet surface mass balance variability (1988–2004) from calibrated Polar MM5 output. J. Climate, 19, 2783–2800.

Cappelen, J., Ed., 2009: DMI monthly climate data collection 1768-2008, Denmark, The Faroe Islands and Greenland. Dansk Meterologisk Institut Tech. Rep. 09-05, 53 pp.

Cassano, J., J. E. Box, D. Bromwich, L. Li, and K. Steffen, 2001: Verification of polar MM5 simulations of Greenland’s atmospheric circulation. J. Geophys. Res., 106 (D24), 33 867–33 890.

Durre, I., R. S. Vose, and D. B. Wuertz, 2006: Overview of the Integrated Global Radiosonde Archive. J. Climate, 19, 53–68.

Hanna, E., J. McConnell, S. Das, J. Cappelen, and A. Stephens, 2006: Observed and modeled Greenland Ice Sheet snow accumulation, 1958–2003, and links with regional climate forcing. J. Climate, 19, 344–358.

Krabill, W., and Coauthors, 2000: Greenland ice sheet: High-elevation balance and peripheral thinning. Science, 289, 428−430.

Liang S., J. Stroeve, and J. E. Box, 2005: Mapping daily snow/ice shortwave broadband albedo from Moderate Resolution Imaging Spectroradiometer (MODIS): The improved direct retrieval algorithm and validation with Greenland in situ measurement. J. Geophys. Res., 110, D10109, doi:10.1029/2004JD005493.

Liu, H., L. Wang, and K. Jezek, 2005: Wavelet-based edge detection approach to derivation of snow-melt onset, duration and extent from satellite passive microwave measurements.

Luthcke, S. B., and Coauthors, 2006: Recent Greenland ice mass loss by drainage system from satellite gravity observations. Science, 24, 1286–1289.

Mosley-Thompson, E., and Coauthors, 2001: Local to regional-scale variability of annual net accumulation on the Greenland ice sheet from PARCA cores. J. Geophys. Res., 106 (D24), 33 839–33 851.

Mote, T. L., 2007: Greenland surface melt trends 1973-2007: Evidence of a large increase in 2007. Geophys. Res. Lett., 34, L22507, doi:10.1029/2007GL031976. S190 | august 2009

—, and M. R. Anderson, 1995: Variations in melt on the Greenland Ice Sheet based on passive microwave measurements. J. Glaciol., 41, 51–60.

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Tedesco, M., X. Fettweis, M. van den Broeke, R. van de Wal, and P. Smeets, 2008: Extreme snowmelt in northern Greenland during summer 2008. Eos, Trans. Amer. Geophys. Union, 89, 391, 10.1029/2008EO410004.

van de Wal, R. S. W., W. Greuell, M. R. van den Broeke, C. H. Reijmer, and J. Oerlemans, 2006: Surface mass-balance observations and automatic weather station data along a transect near Kangerlussuaq, West Greenland. Ann. Glaciol., 42, 311–316.

Zwally, H. J., M. B. Giovinetto, J. Li, H. G. Cornejo, M. A. Beckley, A. C. Brenner, J. Saba, and Y. Donghui, 2005: Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise: 1992–2002. J. Glaciol., 51, 509–527.

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