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Abstract. Surface mass loss from the Greenland ice sheet (GrIS) hasaccelerated over the past decades, mainly due to enhanced surface meltingand liquid water runoff in response to atmospheric warming. A large portionof runoff from the GrIS originates from exposure of the darker bare ice inthe ablation zone when the overlying snow melts, where surface albedo playsa critical role in modulating the energy available for melting. In thisregard, it is imperative to understand the processes governing albedovariability to accurately project future mass loss from the GrIS. Bare-icealbedo is spatially and temporally variable and contingent on non-linearfeedbacks and the presence of light-absorbing constituents. An assessment ofmodels aiming at simulating albedo variability and associated impacts onmeltwater production is crucial for improving our understanding of theprocesses governing these feedbacks and, in turn, surface mass loss fromGreenland. Here, we report the results of a comparison of the bare-iceextent and albedo simulated by the regional climate model ModèleAtmosphérique Régional (MAR) with satellite imagery from theModerate Resolution Imaging Spectroradiometer (MODIS) for the GrIS below70∘ N. Our findings suggest that MAR overestimates bare-ice albedoby 22.8 % on average in this area during the 2000–2021 period with respectto the estimates obtained from MODIS. Using an energy balance model toparameterize meltwater production, we find this bare-ice albedo bias canlead to an underestimation of total meltwater production from the bare-icezone below 70∘ N of 42.8 % during the summers of 2000–2021. 

We calculate a regional surface “melt potential” index (MPI) over Antarctic ice shelves that describes the frequency (MPI-freq; %) and intensity (MPI-int; K) of daily maximum summer temperatures exceeding a melt threshold of 273.15 K. This is used to determine which ice shelves are vulnerable to melt-induced hydrofracture and is calculated using near-surface temperature output for each summer from 1979/80 to 2018/19 from two high-resolution regional atmospheric model hindcasts (using the MetUM and HIRHAM5). MPI is highest for Antarctic Peninsula ice shelves (MPI-freq 23%–35%, MPI-int 1.2–2.1 K), lowest (2%–3%, <0 K) for the Ronne–Filchner and Ross ice shelves, and around 10%–24% and 0.6–1.7 K for the other West and East Antarctic ice shelves. Hotspots of MPI are apparent over many ice shelves, and they also show a decreasing trend in MPI-freq. The regional circulation patterns associated with high MPI values over West and East Antarctic ice shelves are remarkably consistent for their respective region but tied to different large-scale climate forcings. The West Antarctic circulation resembles the central Pacific El Niño pattern with a stationary Rossby wave and a strong anticyclone over the high-latitude South Pacific. By contrast, the East Antarctic circulation comprises a zonally symmetric negative Southern Annular Mode pattern with a strong regional anticyclone on the plateau and enhanced coastal easterlies/weakened Southern Ocean westerlies. Values of MPI are 3–4 times larger for a lower temperature/melt threshold of 271.15 K used in a sensitivity test, as melting can occur at temperatures lower than 273.15 K depending on snowpack properties.