). However, more recent work recorded substantial glacial advance during several years between 2000 and 2010 (Box and Decker, 2011; Murray et al., 2015), which may suggest surging is continuing at Ryder Glacier. Thus it remains unclear whether these advances were internally or externally controlled and whether Ryder Glacier is of true surge-type requires further study.
Generally, surge type glaciers have not been systematically identified across Greenland, apart from in eastern Greenland (Jiskoot et al., 2003; Pritchard et al., 2005). As such, large uncertainties remain as to the nature of surge-type glaciers in northern Greenland, and the possible surge mechanisms have been little-studied. Thus, with several glaciers in northern Greenland having been referred to as “surge type” there is an important need for further research to provide a comprehensive account of surge behavior in northern Greenland and to separate this behavior from changes driven by external forcing.
An important consideration in northern Greenland is the region's sensitivity to future climate change. During the period 2081-2100, average Arctic air temperatures are expected to be 4.2°C warmer than present under Representative Concentration Pathway (RCP) 4.5 and 8.3°C warmer under RCP8.5 (Collins et al., 2013).
As northern Greenland experiences the lowest accumulation rates across the ice sheet (Goelzer et al., 2013) and warming in these high latitudes is expected to be greatest (Gregory and Huybrechts, 2006), it is likely the northern regions of the ice sheet could be more sensitive to future climate change. However, this will also be dependent on how much additional precipitation may be delivered by a warmer atmosphere. Of particular concern to northern Greenland is that simulations of surface melt show the largest amplification in northern Greenland (Fettweis et al., 2012), due to reduced sea ice cover as a result of increased air temperatures (Mernild et al., 2010; Franco et al., 2011). Recent work has also shown an exceptional atmospheric ridge led to greater runoff, low albedo, and higher surface temperatures in the northern regions of the GrIS during 2015 (Tedesco et al., 2016). Goelzer et al. (2013) also showed large negative surface mass balance anomalies to occur around the north coast of Greenland between 2091 and 2100 obtained from a positive degree day model relative to 1989–2008 reference period. Recent studies in northern Greenland have also suggested that increased temperatures and subsequent enhanced surface melt have the potential to weaken floating ice tongues (Johannessen et al., 2013). While several of the glaciers in northern Greenland have shown acceleration and retreat (Figure 7), this is not ubiquitous and ambiguity exists as to the velocity response of northern Greenland outlet glaciers to ice tongue loss in the future.
At Petermann Glacier, future projections driven by atmospheric warming (A1B scenario) show the glacier to primarily lose mass by surface melt between 2000 and 2100, which is in contrast to Helheim and Kangerdlugssuaq glaciers, which instead lose mass via dynamic mechanisms (Nick et al., 2013). Further projections between 2100 and 2200, however, showed dynamic mass losses through increased rates of submarine melt to become far greater at Petermann (Nick et al., 2013). Few other studies have considered outlet glacier response to future climate change at specific outlets in northern Greenland. Thus, substantial uncertainty remains as to the regions sensitivity to future atmospheric and oceanic temperature changes. We therefore suggest further consideration of terminus changes, particularly the loss of floating ice tongues across the entirety of northern Greenland, their effect on ice dynamics, and their relationship to atmospheric/oceanic temperatures, is necessary to better understand and predict future changes under a warmer climate.
Northern Greenland is an important region of the GrIS because it consists of large fast-flowing marine-terminating outlet glaciers, draining a significant area of the ice sheet (coll