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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 imple-
ment dEBM-simple, a simplified version of the diurnal En-
ergy 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 up-
per 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.
