Increased Runoff from Melt from the Greenland Ice Sheet: A Response to Global Warming

Abstract

The authors attribute significantly increased Greenland summer warmth and Greenland Ice Sheet melt and runoff since 1990 to global warming. Southern Greenland coastal and Northern Hemisphere summer temperatures were uncorrelated between the 1960s and early 1990s but were significantly positively correlated thereafter. This relationship appears to have been modulated by the North Atlantic Oscillation, whose summer index was significantly (negatively) correlated with southern Greenland summer temperatures until the early 1990s but not thereafter. Significant warming in southern Greenland since ϳ1990, as also evidenced from Swiss Camp on the west flank of the ice sheet, therefore reflects general Northern Hemisphere and global warming. Summer 2003 was the warmest since at least 1958 in coastal southern Greenland. The second warmest coastal summer 2005 had the most extensive anomalously warm conditions over the ablation zone of the ice sheet, which caused a record melt extent. The year 2006 was the third warmest in coastal southern Greenland and had the third-highest modeled runoff in the last 49 yr from the ice sheet; five of the nine highest runoff years occurred since 2001 inclusive. Significantly rising runoff since 1958 was largely compensated by increased precipitation and snow accumulation. Also, as observed since 1987 in a single composite record at Summit, summer temperatures near the top of the ice sheet have declined slightly but not significantly, suggesting the overall ice sheet is experiencing a dichotomous response to the recent general warming: possible reasons include the ice sheet's high thermal inertia, higher atmospheric cooling, or changes in regional wind, cloud, and/or radiation patterns.

Spatially extensive estimates of annual accumulation in the dry snow zone of the Greenland Ice Sheet determined from radar altimetry

“…Observations show that surface melt extent and duration have increased dramatically since the late 1970s (Abdalati and Steffen, 1997;Steffen et al, 2004;Mote, 2007;Hanna et al, 2008). Meanwhile, there are reports of an increase in the surface elevation at higher altitudes since 1990 (Krabill et al, 2000;Nghiem et al, 2005;Hanna et al, 2006), supporting calibrated climate models which show that some regions of the ice sheet have experienced higher than average accumulation rates, especially in the south (Burgess et al, 2010).…”

“…1). The estimates obtained are compared with snow accumulation rates derived from a weather prediction numerical model run retrospectively using data from the European Centre for Medium-Range Weather Forecast (ECMWF) 45-year (1957-2002) reanalysis ERA-40 and ECMWF operational analysis from 2002 (Hanna et al, 2005(Hanna et al, , 2006(Hanna et al, and 2008. This model has been recently corrected and calibrated for Greenland with recent field measurements .…”

Sensitivity of Greenland Ice Sheet surface mass balance to surface albedo parameterization: a study with a regional climate model

“…After a 30-yr period during which the GrIS was in approximate mass balance (i.e. the mass gain by precipitation was approximately equal to the mass loss by surface runoff and solid ice discharge), the mass balance has turned negative in the last 20 yr, with a larger melt extent (Fettweis et al, 2011), increasing surface runoff Hanna et al, 2008) and increased glacier discharge (Nick et al, 2009;Rignot et al, 2011). In the last decade, contributions made to the total mass loss of ∼ 2400 Gt, were for ∼ 60 % accounted for by enhanced runoff and for ∼ 40 % by enhanced discharge Rignot et al, 2008).…”

The seasonal cycle and interannual variability of surface energy balance and melt in the ablation zone of the west Greenland ice sheet

“…Strong interactions exist between surface meltwater production and the sliding behaviour of the ice sheet in west Greenland (Zwally et al, 2005;Van de Wal et al, 2008;Joughin et al, 2008;Shepherd et al, 2009), a process that is linked to the formation and decay of subglacial meltwater channels (Schoof, 2010). The increase in runoff since 1990, following atmospheric warming (Box and Cohen, 2006;Hanna et al, 2008), explains more than half of the recent mass loss of the GrIS ( Van den Broeke, 2009a). In the warm summers of 2007 and 2010 (Tedesco et al, 2008(Tedesco et al, , 2011, melting on the GrIS exceeded 600 Gt yr −1 , an increase of >60 % compared to the 1961-1990 average.…”