Abstract
Abstract. Surface melting of the Greenland Ice Sheet contributes a large amount to current and future sea level rise. Increased surface melt may lower the reflectivity of the ice sheet surface and thereby increase melt rates: the so-called melt–albedo feedback describes this self-sustaining increase in surface melting. In order to test the effect of the melt–albedo feedback in a prognostic ice sheet model, we implement dEBM-simple, a simplified version of the diurnal Energy Balance Model dEBM, in the Parallel Ice Sheet Model (PISM). The implementation includes a simple representation of the melt–albedo feedback and can thereby replace the positive-degree-day melt scheme. Using PISM-dEBM-simple, we find that this feedback increases ice loss through surface warming by 60 % until 2300 for the high-emission scenario RCP8.5 when compared to a scenario in which the albedo remains constant at its present-day values. With an increase of 90 % compared to a fixed-albedo scenario, 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 4-fold 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)
With dEBMsimple implemented in Parallel Ice Sheet Model (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
In comparing the ice loss with PISM-diurnal energy balance model (dEBM)-simple in the RCP8.5 scenario to ice loss computed with PISM-PDD, we find that the positive-degree-day method increases losses by 12 % until 2100 and by 47 % by 2300
Summary
The Greenland Ice Sheet is currently one of the main contributors to sea level rise (Frederikse et al, 2020). 35 % of the observed mass loss during the last 40 years is attributed to changes in surface mass balance, and 65 % of the mass loss is due to an increase in discharge fluxes (Mouginot et al, 2019). The contribution of changes in surface mass balance is expected to increase with ongoing warming (Shepherd 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). In addition to the darkening through melt, studies suggest a positive feedback mechanism between mi-
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