Greenland

J. Box¹, J. Cappelen², D. Bromwich¹, L.-S. Bai¹, T. Mote³, B. Veenhuis⁴, N. Mikkelsen⁵, and A. Weidick⁵

¹Byrd Polar Research Center, The Ohio State University, Columbus, Ohio
²Danish Meteorological Institute, Copenhagen, Denmark
³Department of Geography, University of Georgia, Atlanta, Georgia
⁴Department of Meteorology, The Florida State University, Tallahassee, Florida
⁵Geologic Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark

Summary

Warming has continued around Greenland in 2007, culminating in record setting (since 1970s) melt area and amplified absorption of solar radiation. Greenland's largest glacier, among a majority of others, continued its retreat. The ice sheet lost at least 100 cubic km (24 cubic miles) of ice, making it one of the largest single contributors to global sea level rise.

Overview

Greenland climate records indicate regional warming in 2007, with statistically significant positive (warm) annual temperature anomalies in the 1.3° to 2.7°C range for coastal stations and 1.3°C for the inland ice sheet with respect to 1971–2000 averages. Seasonal temperature anomalies were largest in winter but not positive in every season. Upper air temperatures indicate lower- to midtropospheric warm anomalies in all seasons above sounding stations surrounding Greenland. Noteworthy are western and southern locations where midtropospheric anomalies exceed those observed at the surface. Ice sheet surface melt duration anomalies were up to 53 days longer than the 1973–2000 average, based on passive microwave remote sensing. MODIS-derived surface albedo anomalies in 2007 versus the 2000–07 period were persistently negative, consistent with extensive surface melting. Greenland's largest glacier continued its recession, with ice flushing out from an embayment thought to have been ice filled since at least the onset of the Little Ice Age. The overall ice sheet mass budget was likely in mass deficit by at least 100 km³ yr^–1.

Coastal surface air temperatures

Warm (positive) anomalies predominated in 2007, relative to the last 50-yr period (1958–2007), when the most reliable continuous surface air temperature records are available from a collection of stations around the island (Cappelen et al. 2007, 2008). Exceptions included an anomalously cold winter at Pittufik (northwest), an unusually cold summer and autumn at Nuuk (southwest), and an anomalously cold summer at Upernavik. The Z-scores exceeding ±1.0 or ±2.0 indicate anomalies exceeding the most common 66% or 95% of the observed cases, respectively (Table G1). At Upernavik (northwest) the spring temperature was the warmest in the past 50 yr, and at Nuuk (southwest) the summer temperature was the coldest in the past 50 yr. The only anomalies that were significant annually, that is, with Z-scores ≥1.0, were warm anomalies for 2007 annual means.

Table G1. Greenland station surface air temperature anomalies by season, 2007 vs 1971–2000. Anomalies are in °C. Bold values indicate values that meet or exceed 1 Z-score.

Upper air temperatures

Upper air sounding data available from the Integrated Global Radiosonde Archive (Durre et al. 2006) indicate for Greenland in 2007 a continued pattern of lower- to midtropospheric warming and lower-stratospheric cooling, consistent with trends since 1964 (Box and Cohen 2006). In the lower troposphere at the 850-hPa level (1.1–1.5-km altitude), for example, annual temperature anomalies were between +0.6° and +1.5°C at sites surrounding the island, relative to the 1971–2000 average. Seasonal anomalies were largest in winter with up to +8.1°C at 1,000 hPa at the Aasiaat/Egedesminde sounding site, with smaller positive anomalies elsewhere in almost all seasons. At the upper limit of mandatory observational levels, (20 hPa, in the lower–mid stratosphere), –11.6°C anomalies are evident. Large lower-stratospheric temperature anomalies are not necessarily abnormal given the relatively large observed temperature variability due in part to much lower atmospheric mass (e.g., Christy and Drouilhet 1994) and given the fact that mid-stratospheric anomalies tend to mirror lower troposapheric anomalies (e.g., Liu and Schuurmans, 1990; Wong and Wang, 2000). Summer anomalies above southern Greenland balloon launching sites at the 850 and 600-hPa levels were between +0.2° and +1.3°C.

Greenland ice sheet melt extent

Passive microwave observations indicate summer 2007 (June–August) Surface Melt Duration (SMD) was greater than any other observed summer since records began in 1973 (Mote 2007). The ice sheet area undergoing surface melt was 60% greater in 2007 than the next highest year (1998). Summer 2007 had 20 days more melt than average (1973–2000) across nearly all of the regions that exhibit melting. Up to 53 more days of melting than average was observed for elevations in the 2,000- to 2,400-m above sea level range between the north and south domes of the ice sheet (Fig. G1).

Ice sheet precipitation, evaporation, and meltwater runoff

Polar MM5 climate data assimilation model runs spanning 50 yr (1958–2007), 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 year 2007 precipitation and accumulation was not abnormal despite a +10 km³ decade^–1 positive total precipitation trend over the 1958–2007 period. Surface water vapor fluxes were within an insignificant inter-annual range. In accordance with a +1.3°C year 2007 annual mean temperature anomaly, the fraction of precipitation that fell as rain instead of snow, surface meltwater production, and meltwater runoff were well above the 1971–2000 mean (Table G2). Due to abnormally large mass loss by meltwater runoff despite normal snow accumulation, melt and more frequent rainfall darkened the snow and ice surface (Fig. G2).

Figure G1. Surface melt duration departure from average for summer (Jun–Aug) 2007 from SSM /I; units are days. The average is based on the summers from 1973 to 2000 (excluding 1975, 1977, and 1978). Only departures >10 days are included. (Figure after Mote 2007)		Figure G2. Albedo anomaly (unitless) for 8–23 Aug (days 220–235) 2007 vs the 2000–07 average (from algorithm based on Liang et al. 2005).

Table G2. Greenland ice sheet surface mass balance parameters: 2007 departures from 1971–2000 average (adapted from Box et al. 2006).

Glacier changes

The terminus of Greenland's largest glacier, the Jakobshavn's Isbrae near the town of Ilulissat, retreated 0 to 500 m in 2007 (Fig. G3), continuing a retreat that began summer 2001 with a dramatic 11-km floating ice collapse (Weidick and Bennike 2007). The large ice lagoon called Tissarissoq at the south side of the fjord was flushed of ice by the end of the summer, ice-free probably for the first time since at least the onset of the Little Ice Age (ca. 0.4–0.1 ky BP). It is possible that Tissarissoq was ice-free before that time during the medieval warm period (ca. 1.1–0.5 ky BP).

Figure G3. Front position of the Ilulissat (Jakobshavn Isbrae) glacier in 2007 and earlier years, based on Weidick and Bennike (2007). The image mosaic is from Jun 2003 Landsat and ASTER images. (click for larger image).

References

Bales, R. C., E. Mosley-Thompson, and J. R. McConnell, 2001: Variability of accumulation in northwest Greenland over the past 250 years. Geophys. Res. Lett., 28, 2679–2682.

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

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

Cappelen, J., E. V. Laursen, P. V. Jørgensen, and C. Kern-Hansen, 2007: DMI monthly Climate Data Collection 1768–2006, Denmark, The Faroe Islands and Greenland. Danish Meteorological Institute, Tech. Rep. 07-06, 53 pp.

Christy, J. R., and S. J. Drouilhet, 1994: Variability in daily, zonal mean lower-stratospheric temperatures. J. Climate, 7, 106–120.

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.

Liu, Q., and C. J. E. Schuurmans, 1990: The correlation of tropospheric and stratospheric temperatures and its effect on the detection of climate changes, Geophys. Res. Letters, 17, 1085–1088.

Mosley-Thompson, E., and Coauthors, 2001: Local to regional-scale variability of Greenland accumulation 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.

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

Wong, S., and W.-C. Wang, 2000: Interhemispheric asymmetry in the seasonal variation of the zonal mean tropopause, J. Geophys. Res., 105, No. D21, p. 26,645 (2000JD900475)

October 14, 2008

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