Accelerating changes in ice mass within Greenland, and the ice sheet’s sensitivity to atmospheric forcing

Abstract

From early 2003 to mid-2013, the total mass of ice in Greenland declined at a progressively increasing rate. In mid-2013, an abrupt reversal occurred, and very little net ice loss occurred in the next 12–18 months. Gravity Recovery and Climate Experiment (GRACE) and global positioning system (GPS) observations reveal that the spatial patterns of the sustained acceleration and the abrupt deceleration in mass loss are similar. The strongest accelerations tracked the phase of the North Atlantic Oscillation (NAO). The negative phase of the NAO enhances summertime warming and insolation while reducing snowfall, especially in west Greenland, driving surface mass balance (SMB) more negative, as illustrated using the regional climate model MAR. The spatial pattern of accelerating mass changes reflects the geography of NAO-driven shifts in atmospheric forcing and the ice sheet’s sensitivity to that forcing. We infer that southwest Greenland will become a major future contributor to sea level rise.

Decelerated Greenland Ice Sheet Melt Driven by Positive Summer North Atlantic Oscillation

“…However, recent GRACE and GPS observations showed the abrupt deceleration of the GrIS melt since 2013 (Figure a). The GrIS lost mass at a rate of about 102 Gt/year in early 2003, increased to 393 Gt/year during 2012–2013, but suddenly reduced to no more than 75 Gt/year during 2013–2014 (Bevis et al, ). It is suggested that this deceleration is due to the increased snowfall accumulation driven by the positive phase of sNAO (Chen et al, ; Folland et al, ).…”

“…The time scale of this deceleration is of importance on reducing the uncertainty of future projection of the GrIS variability and global sea level change. It is suggested that the deceleration during 2013–2014 has ended because the sNAO turned to negative in 2015 again (Bevis et al, ). However, Figure a shows that, except for the unusual summer melting in 2012 (Hanna et al, ), the total melt area calculated with daily surface melt data in Greenland from National Snow and Ice Data Center in the other years in the 2010s are all less than those exhibited during the melt seasons of the previous decade.…”

Controls on the Transport of Meltwater From the Southern Greenland Ice Sheet in the Labrador Sea

“…We also identify which mechanisms are necessary for effective offshore transport of meltwater, and how their impact is different on meltwater originating along the West and East Greenland coasts. This differentiation is important because meltwater inputs along West and East Greenland are characterized by different temporal variability and volume, with the largest increases in runoff over the last few years having occurred in Southwest Greenland (Bevis et al, ; Luo et al, ). Thus, identifying whether mechanisms driving offshore export of meltwater have different impacts on West and East Greenland meltwater runoff is needed to understand the effects of the predicted increase in meltwater runoff (Fettweis et al, ) on the surface hydrography in the central Labrador Sea.…”

Historical and Future Roles of Internal Atmospheric Variability in Modulating Summertime Greenland Ice Sheet Melt

“…The NAO is associated with changes in the strength and position of the jet stream (Woollings & Blackburn, 2012), affecting temperatures over Greenland and north and central Europe (Chylek et al, 2004). These NAO effects are often discussed in the context of winter climate; however, the NAO has also been shown to have an important role also in summer, when conditions are conducive to Greenland ice melt (Bevis et al, 2019; Fettweis et al, 2013; Folland et al, 2009; van Angelen et al, 2014). This connection is reflected in both observations (Bevis et al, 2019; Box et al, 2012) and models (Ding et al, 2014; Hahn et al, 2018).…”

“…These NAO effects are often discussed in the context of winter climate; however, the NAO has also been shown to have an important role also in summer, when conditions are conducive to Greenland ice melt (Bevis et al, 2019; Fettweis et al, 2013; Folland et al, 2009; van Angelen et al, 2014). This connection is reflected in both observations (Bevis et al, 2019; Box et al, 2012) and models (Ding et al, 2014; Hahn et al, 2018). Notably, the recent 2013–2014 pause in the west coast GrIS melting coincided with a strong and positive NAO (Bevis et al, 2019).…”