Divergent trajectories of Antarctic surface melt under two twenty-first-century climate scenarios

Abstract

Ice shelves modulate Antarctic contributions to sea-level rise 1 and thereby represent a critical, climate-sensitive interface between the Antarctic ice sheet and the global ocean. Following rapid atmospheric warming over the past decades 2,3 , Antarctic Peninsula ice shelves have progressively retreated 4 , at times catastrophically 5 . This decay supports hypotheses of thermal limits of viability for ice shelves via surface melt forcing 3,5,6 . Here we use a polar-adapted regional climate model 7 and satellite observations 8 to quantify the nonlinear relationship between surface melting and summer air temperature. Combining observations and multimodel simulations, we examine melt evolution and intensification before observed ice shelf collapse on the Antarctic Peninsula. We then assess the twenty-first-century evolution of surface melt across Antarctica under intermediate and high emissions climate scenarios. Our projections reveal a scenario-independent doubling of Antarctic-wide melt by 2050. Between 2050 and 2100, however, significant divergence in melt occurs between the two climate scenarios. Under the high emissions pathway by 2100, melt on several ice shelves approaches or surpasses intensities that have historically been associated with ice shelf collapse, at least on the northeast Antarctic Peninsula.Antarctic ice shelves have undergone widespread and accelerated thinning and retreat in recent decades in response to coupled atmospheric and oceanic forcing [3][4][5]9,10 . On the Antarctic Peninsula (AP), this recession has been particularly pronounced and punctuated with near-uniform, abrupt collapses of Larsen A, Prince Gustav, and Larsen B ice shelves occurring since 1995 ( Fig. 1). Across this region, recent atmospheric warming has exceeded global average rates 2 and current surface melting levels are unprecedented over the past millennium on the northeast AP (ref. 11). This warming and melt intensification has directly led to an expansion of meltwater ponding, and the resultant hydrofracturing is considered a leading mechanism of AP ice shelf collapse 3,5,12 .All Antarctic ice shelves experience surface melting today 7,8 , yet ocean-induced basal melting at present dominates ice shelf mass losses, particularly outside of the AP (refs 9,10). Nevertheless, surface melt intensities approach those of the AP elsewhere in Antarctica (Fig. 1c), meltwater ponding exists beyond the AP (refs 13,14), and strong basal melting can hasten ice shelf destabilization 4,10 . The question therefore arises, are recent ice shelf dynamics on the AP indicative of forthcoming changes elsewhere in Antarctica? Understanding the present-day and future viability of all Antarctic ice shelves requires an improved characterization of the sensitivity of ice shelves to temperature change, a better historical context for AP melt acceleration and ice shelf collapse, and robust projections of future pan-Antarctic change.Air temperature is often used to parameterize surface melt owing to several important physical linkages with the sur...

Widespread movement of meltwater onto and across Antarctic ice shelves

“…If water can access areas vulnerable to hydraulically driven fracture, ice-shelves can collapse, which accelerates upstream thinning 4 . How different parts of Antarctica's surface drainage system will respond to increased surface melting 6 will vary. Rock-melt-thinning feedbacks may be most effective where nunataks exist upstream of ice shelves that, owing to their stress state, are vulnerable to collapse.…”

Basin-scale heterogeneity in Antarctic precipitation and its impact on surface mass variability

“…They are also important in understanding future change, during which regional variability will be superim-posed on by a strong secular trend towards greater precipitation (Palerme et al, 2016;Frieler et al, 2015;Previdi and Polvani, 2016;Lenaerts et al, 2016) and increased lowelevation surface melting (Fyke et al, 2010;Trusel et al, 2015). However, they are characteristically hampered by either short time series length, sparse point data, observational uncertainty, a mixture of forced and natural variability signals or a combination of all of these.…”

Identification of Air Masses Responsible for Warm Events on the East Antarctic Coast

“…In many coastal Antarctic regions, summer temperatures have reached positive values and triggered surface melt of glaciers and ice shelves (Trusel et al 2015). For example, warming trends observed in the Antarctic Peninsula (AP) and West Antarctica (WA) in the past decades (Vaughan et al 2003;Bromwich et al 2012) have been associated with increase in mass loss Sutterley et al 2014).…”