Abstract
Surface melting of the Greenland Ice Sheet contributes a large amount to current and future sea-level rise. Increased surface melt, algae growth, debris, and dust deposition lower the reflectivity of the ice surface and thereby increase melt rates: the so-called melt-albedo feedback describes this potentially self-sustaining increase in surface melting. Here we present a simplified version of the diurnal Energy Balance Model (dEBM-simple) which is implemented as a surface melt module in the Parallel Ice Sheet Model (PISM). dEBM-simple is a modification of diurnal Energy Balance Model (dEBM), a surface melt scheme of intermediate complexity useful for simulations over centennial to multi-millennial timescales. dEBM-simple is computationally efficient, suitable for standalone ice-sheet modeling and includes a simple representation of the melt-albedo feedback. Using dEBM-simple and PISM, we find that this feedback increases ice loss until 2300 through surface warming by 60 % for the high-emission scenario RCP8.5. With an increase of 90 %, the effect is more pronounced for lower surface warming under RCP2.6. Furthermore, assuming an immediate darkening of the ice surface over all summer months, we estimate an upper bound for this effect to be +70 % in the RCP8.5 scenario and a more than fourfold increase under RCP2.6. With dEBM-simple implemented in PISM, we find that the melt-albedo feedback is an essential contributor to mass loss in dynamic simulations of the Greenland Ice Sheet under future warming.
Highlights
The Greenland Ice Sheet is currently one of the main contributors to sea-level rise (Frederikse et al, 2020)
We present a simplified version of the diurnal Energy Balance Model which is implemented as a surface melt module in 5 the Parallel Ice Sheet Model (PISM). dEBM-simple is a modification of diurnal Energy Balance Model, a surface melt scheme of intermediate complexity useful for simulations over centennial to multi-millennial timescales. dEBM-simple is computationally efficient, suitable for standalone ice-sheet modeling and includes a simple representation of the melt– albedo feedback
With dEBM-simple implemented in PISM, we find that the melt–albedo feedback is an essential contributor to mass loss in dynamic simulations of the Greenland Ice Sheet under future warming
Summary
The Greenland Ice Sheet is currently one of the main contributors to sea-level rise (Frederikse et al, 2020). Observations show that the surface of the Greenland Ice Sheet has been darkening over the last decades (He et al, 2013; Tedesco et al, 2016), and projections show that it is likely to darken further with increasing warming (Tedesco et al, 2016). Studies suggest a positive feedback mechanism between microbes, minerals, and melting, 10 where algae-induced melting releases ice-bound dust, which in turn increases glacier algal blooms, leading to more melt (Di Mauro et al, 2020; McCutcheon et al, 2021). This melt–albedo feedback is usually interrupted by winter snow accumulation and snow events in summer (Gardner and Sharp, 2010; Noël et al, 2015). In the light of recent extreme melting events as in 2010 (Tedesco et al, 2011), 2012 (Nghiem et al, 2012) or 2019 (Tedesco and Fettweis, 2020), where large parts of the surface area were covered by melt water and darker than usual, it is important to model the response of the ice sheet to such 15 large-scale changes in albedo
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