"Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers," by J. E. Box, X. Fettweis, J. C. Stroeve, M. Tedesco, D. K. Hall & K. Steffen

The Cryosphere Discuss. 


Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers


J. E. Box(1,2,*), X. Fettweis(3), J. C. Stroeve(4,5), M. Tedesco(6), D. K. Hall(7) and K. Steffen(5)


1Department of Geography, The Ohio State University, Columbus, OH, USA
2Byrd Polar Research Center, The Ohio State University, Columbus, OH, USA
3Department of Geography, University of Liege, Belgium
4National Snow and Ice Data Center, Boulder, CO, USA
5Cooperative Institute for Research in Environmental Sciences,
University of Colorado, Boulder, CO, USA
6The City University of New York, New York, NY, USA
7NASA Goddard Space Flight Center, Greenbelt, MD, USA


*Correspondence: box.11@osu.edu


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–derived surface albedo with calibrated regional climate modeled surface air temperature and surface downward solar irradiance, we determine the spatial dependence and quantitative impact of the ice sheet albedo feedback over twelve summer periods beginning in 2000. We find that while albedo feedback defined by the change in net solar shortwave flux and temperature over time is positive over 97% of the ice sheet, when defined using paired annual anomalies, a second order negative feedback is evident over 63% of the accumulation area. This negative feedback damps the accumulation area response to warming due to a positive correlation between snowfall and surface air temperature anomalies. Positive anomaly–gauged feedback concentrated in the ablation area  accounts for more than half of the overall increase in melting when satellite derived melt duration is used to define the timing when net shortwave flux is sunk into melting. Abnormally strong 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 shortwave flux, 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 infrared and solar radiation for the high elevation accumulation area approached positive values during this period. Thus, it is reasonable  to expect 100% melt area over the ice sheet within another similar decade of warming.

http://bprc.osu.edu/~jbox/temp/Box%20et%20al.%202012%20-%20TCD%20-%20resubmitted%20after%20review%20round%202.pdf