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Abstract
Abstract. A combined analysis of remote sensing observations, regional climate model (RCM) outputs and reanalysis data over the Greenland ice sheet provides evidence that multiple records were set during summer 2012. Melt extent was the largest in the satellite era (extending up to ∼97% of the ice sheet) and melting lasted up to ∼2 months longer than the 1979–2011 mean. Model results indicate that near surface temperature was ∼3 standard deviations (σ) above the 1958–2011 mean, while surface mass balance (SMB) was ∼3σ below the mean and runoff was 3.9σ above the mean over the same period. Albedo, exposure of bare ice and surface mass balance also set new records, as did the total mass balance with summer and annual mass changes of, respectively, −627 Gt and −574 Gt, 2σ below the 2003–2012 mean. We identify persistent anticyclonic conditions over Greenland associated with anomalies in the North Atlantic Oscillation (NAO), changes in surface conditions (e.g., albedo, surface temperature) and preconditioning of surface properties from recent extreme melting as major driving mechanisms for the 2012 records. Less positive if not increasingly negative SMB will likely occur should these characteristics persist.
Highlights
During the past decade, surface melting over the Greenland Ice Sheet (GrIS) has been increasing (e.g., Hanna et al, 2008; Fettweis et al, 2013a; Mote, 2007; Tedesco et al, 2008, 2011, Mernild et al, 2011), with results from regional climate models, in situ observations and satellite data revealing accelerating ice sheet mass loss
Near-realtime DMSP Sensor Microwave Imager/Sounder (SSMIS) Daily Polar Gridded Brightness Temperatures and Earth Scalable (EASE)-Grid Brightness Temperatures are available through National Snow and Ice Data Center (NSIDC) and are used here for the analysis reported in the following for the 2012 season
The JJA ice-sheet-wide Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) increased 3.4 ◦C between years 2000 and 2012, from an average value of ∼ −9 ◦C in 2000 to −5.6 ◦C in 2012, with a linear fit suggesting an increase of +2.1 ± 0.7 ◦C over the last 13 yr
Summary
Surface melting over the Greenland Ice Sheet (GrIS) has been increasing (e.g., Hanna et al, 2008; Fettweis et al, 2013a; Mote, 2007; Tedesco et al, 2008, 2011, Mernild et al, 2011), with results from regional climate models, in situ observations and satellite data revealing accelerating ice sheet mass loss (van den Broeke et al, 2009; Rignot et al, 2011). Aside from the direct impact of increased runoff on the surface mass balance (SMB) of the GrIS, changes in the meltwater production affect supraglacial, englacial and subglacial processes. The existence of supraglacial lakes, whose formation is driven by meltwater production, increases the ice ablation rate relative to that of bare ice at the surface (e.g., Tedesco et al, 2012a). Rates of meltwater production play a key role in modulating the opening and persistence of surface-tobedrock connections (e.g., hydro-fracturing; e.g., Weertman, 1973; van der Veen, 2007; Catania et al, 2008), which are associated with ice sheet velocity spatio-temporal gradients
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