Abstract
In mid-June 2019, the Greenland ice sheet (GrIS) experienced an extreme early-season melt event. This, coupled with an earlier-than-average melt onset and low prior winter snowfall over western Greenland, led to a rapid decrease in surface albedo and greater solar energy absorption over the melt season. The 2019 melt season resulted in significantly more melt than other recent years, even compared to exceptional melt years previously identified in the moderate-resolution imaging spectroradiometer (MODIS) record. The increased solar radiation absorbance in 2019 warmed the surface and increased the rate of meltwater production. We use two decades of satellite-derived albedo from the MODIS MCD43 record to show a significant and extended decrease in albedo in Greenland during 2019. This decrease, early in the melt season and continuing during peak summer insolation, caused increased radiative forcing of the ice sheet of 2.33 Wm−2 for 2019. Radiative forcing is strongly influenced by the dramatic seasonal differences in surface albedo experienced by any location experiencing persistent and seasonal snow-cover. We also illustrate the utility of the newly developed Landsat-8 albedo product for better capturing the detailed spatial heterogeneity of the landscape, leading to a more refined representation of the surface energy budget. While the MCD43 data accurately capture the albedo for a given 500 m pixel, the higher spatial resolution 30 m Landsat-8 albedos more fully represent the detailed landscape variations.
Highlights
IntroductionFine-grained snow typically has an albedo in the range of ~0.8–0.9, coarse-grained older snow has an albedo of ~0.7–~0.8, and wet snow and bare clean ice of ~0.4–~0.7 [7,8,9]
The MCD43 albedo provided the basis for the majority of the analysis presented in this work, since it is available at a daily frequency from 2000 to present
The albedo decreases caused by the 2019 melt episode are readily visible in the MCD43 shortwave blue-sky albedo in Figures 2 and 3
Summary
Fine-grained snow typically has an albedo in the range of ~0.8–0.9, coarse-grained older snow has an albedo of ~0.7–~0.8, and wet snow and bare clean ice of ~0.4–~0.7 [7,8,9]. This reduced reflectance of solar radiation alters the surface energy budget, with a positive feedback of increasing solar energy absorbance causing an increase in the rate of meltwater production [1,6]
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