Abstract. The Greenland Ice Sheet is losing mass at a significant rate,
driven in part by increasing surface-melt-induced runoff. Because the ice
sheet's surface melt is closely connected to changes in the surface albedo,
studying multidecadal changes in the ice sheet's albedo offers insight into
surface melt and associated changes in its surface mass balance. Here, we
first analyse the CM SAF Cloud, Albedo and
Surface Radiation dataset from AVHRR data second edition (CLARA-A2) Surface Albedo (SAL),
covering 1982–2015, to obtain decadal albedo trends for each summer month.
We also examine the rates of albedo change during the early summer,
supported with atmospheric reanalysis data from MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, version 2), to discern changes
in the intensity of early summer melt, and their likely drivers. We find
that rates of albedo decrease during summer melt have accelerated during the
2000s relative to the early 1980s and that the surface albedos now often
decrease to values typical of bare ice at elevations 50–100 m higher on
the ice sheet. The southern margins exhibit the opposite behaviour, though,
and we suggest this is due to increasing snowfall over the area. We then subtract ice discharge from the mass balance estimates observed by
the Gravity Recovery and
Climate Experiment (GRACE) satellite mission to estimate surface mass balance. The CLARA-A2 albedo changes are regressed with these data to obtain a summer-aggregated
proxy surface mass balance time series for the summer periods 1982–2015. This
proxy time series is compared with latest regional climate model estimates
from the MAR model to perform an observation-based test on the dominance of
surface runoff in the magnitude and variability of the summer surface mass
balance. We show that the proxy time series agrees with MAR through the
analysed period within the associated uncertainties of the data and methods,
demonstrating and confirming that surface runoff has dominated the rapid
surface mass loss period between the 1990s and 2010s. Finally, we extend the analysis to the drainage basin scale to examine
discharge–albedo relationships. We find little evidence of surface-melt-induced ice flow acceleration at annual timescales.
A Pattern-Based Method For Handling Confidence Measures While Mining Satellite Displacement Field Time Series: Application to Greenland Ice Sheet and Alpine Glaciers