Atmospheric and oceanic climate forcing of the exceptional Greenland ice sheet surface melt in summer 2012

Abstract

The NASA announcement of record surface melting of the Greenland ice sheet in July 2012 led us to examine the atmospheric and oceanic climatic anomalies that are likely to have contributed to these exceptional conditions and also to ask the question of how unusual these anomalies were compared to available records. Our analysis allows us to assess the relative contributions of these two key influences to both the extreme melt event and ongoing climate change. In 2012, as in recent warm summers since 2007, a blocking high pressure feature, associated with negative NAO conditions, was present in the mid-troposphere over Greenland for much of the summer. This circulation pattern advected relatively warm southerly winds over the western flank of the ice sheet, forming a 'heat dome' over Greenland that led to the widespread surface melting. Both sea-surface temperature and sea-ice cover anomalies seem to have played a minimal role in this record melt, relative to atmospheric circulation. Two representative coastal climatological station averages and several individual stations in south, west and north-west Greenland set new surface air temperature records for May, June, July and the whole (JJA) summer. The unusually warm summer 2012 conditions extended to the top of the ice sheet at Summit, where our reanalysed (1994-2012) DMI Summit weather station summer (JJA) temperature series set new record high mean and extreme temperatures in 2012; 3-hourly instantaneous 2-m temperatures reached an exceptional value of 2.2°C at Summit on 11 July 2012. These conditions translated into the record observed ice-sheet wide melt during summer 2012. However, 2012 seems not to be climatically representative of future 'average' summers projected this century. © 2013 Royal Meteorological Society

Future sea level rise constrained by observations and long-term commitment

“…These records are underestimated and therefore not fully linked to global mean temperature by our calibration (Fig. 1D), which is consistent with the suggested influence of natural variability through the North Atlantic oscillation (25,44). Still, the inferred short response times lead to a future contribution above the range of current process-based projections (3).…”

Investigating the local-scale influence of sea ice on Greenland surface melt

“…The GBI is defined as the 500 hPa geopotential height field averaged between 20 and 80 • W, 60 and 80 • N (Fang, 2004;Hanna et al, 2013) and is used as a metric for large-scale atmospheric circulation patterns over Greenland. To remove the influence of the GBI on both SIC and GrIS melt, we performed a partial correlation analysis of SIC in each region and GrIS meltwater production after the trends in GBI were removed (e.g., Cohen et al, 2003).…”

“…Analysis of mid-tropospheric summer (JJA) sea level pressure (SLP) reveal statistically significant increases over Greenland and north of the Canadian Arctic Archipelago coupled with significant negative trends over northern Eurasia and Canada from 1979 to 2014 (Serreze et al, 2016;Bezeau et al, 2015), dominated by a clear shift in the last decade (2005 to 2014) towards large positive SLP anomalies over the central Arctic Ocean and Greenland. This pattern favors both summer sea ice loss (e.g., Wang et al, 2009;Ogi and Wallace, 2007) and Greenland surface melt (Hanna et al, 2013;Mioduszewski et al, 2016;Ballinger et al, 2017). Additionally, advection of warm and humid air masses appears to be the primary factor initiating sea ice melt onset (MO) (Boisvert and Stroeve, 2015;Mortin et al, 2016).…”

Strong wind events across Greenland�s coast and their influence on the ice sheet, sea ice and ocean

“…In peak summer, winds over Greenland are weaker compared to winter, fall and spring, and inland the radiative fluxes are more important than the turbulent heat fluxes [Serreze and Barry, 2005]. Yet, even the summer temperature over Greenland is strongly linked to the atmospheric circulation [Fettweis et al, 2011, Overland et al, 2012, Fettweis et al, 2013 and extremely warm summers have been associated with preceding warm air advection over the ice sheet [Box et al, 2012, Hanna et al, 2014.…”

“…The advection of warm air, in turn, has been linked to an anticyclonic circulation over Greenland that results in warm southerly winds across the western coast [Hanna et al, 2014]. In this chapter, I will investigate the characteristics of onshore winds also across the southeast and east coast of Greenland, and study their effect on the surface energy balance over the ice sheet.…”