Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers

Abstract

Abstract. Greenland ice sheet mass loss has accelerated in the past decade responding to combined glacier discharge and surface melt water runoff increases. During summer, absorbed solar energy, modulated at the surface primarily by albedo, is the dominant factor governing surface melt variability in the ablation area. Using satellite observations of albedo and melt extent with calibrated regional climate model output, we determine the spatial dependence and quantitative impact of the ice sheet albedo feedback in twelve summer periods beginning in 2000. We find that while the albedo feedback is negative over 70 % of the ice sheet, concentrated in the accumulation area above 1500 m, positive feedback prevailing over the ablation area accounts for more than half of the overall increase in melting. Over the ablation area, year 2010 and 2011 absorbed solar energy was more than twice as large as in years 2000–2004. Anomalous anticyclonic circulation, associated with a persistent summer North Atlantic Oscillation extreme since 2007 enabled three amplifying mechanisms to maximize the albedo feedback: (1) increased warm (south) air advection along the western ice sheet increased surface sensible heating that in turn enhanced snow grain metamorphic rates, further reducing albedo; (2) increased surface downward solar irradiance, leading to more surface heating and further albedo reduction; and (3) reduced snowfall rates sustained low albedo, maximizing surface solar heating, progressively lowering albedo over multiple years. The summer net radiation for the high elevation accumulation area approached positive values during this period.