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Thursday, September 6, 2012

Jason Box: High, late August 2012 Greenland ice temperature maintains low ice sheet reflectivity and melting

by Jason Box, The Melt Factor, August 27, 2012

Daily surface temperatures in June-August 2012 have peaked more than 5 C (~9 F) warmer for the whole ice sheet than the 2000-2009 daily averages according to my analysis of ice surface temperatures from  daily NASA MODIS MOD11 satellite derived Land Surface Temperature (LST) retrievals. Over the highest elevations, surface temperatures were nearly 10 C (~18 F) warmer than in the decade of the 2000s, leading to an area of ice sheet surface melting, unprecedented in the satellite observational record beginning in 1978.

Fig. 1. Greenland clear sky ice surface temperature anomaly relative to the 2000-2009 baseline.
To a first approximation, when ice sheet temperature increases, its reflectivity decreases (Box et al. 2012). After a low temperatures on August 10-13, 2012, the surface reflectivity of sunlight (a.k.a. albedo) increased from the accumulation of fresh bright snow (Fig. 2). Then as surface temperatures rose again, above one standard deviation of the 2000-2009 average, the ice sheet albedo again dropped on August 18-23, 2012 below previous observations (since 2000), especially at the intermediate elevations of 1000-1500 m where melting in all likelihood remains active this year. As reported by Marco Tedesco, 2012 melting is already setting the record since the late 1950s, and with this late melt season albedo drop and high surface temperature anomaly, this “Goliath” melt has got to be growing.
Fig. 2. Daily Greenland ice sheet reflectivity (a.k.a. albedo) values spanning nearly 13 years; 2000-2012.
The daily albedo anomaly map (Fig. 3) indicates widespread low reflectivity, especially at the ice sheet periphery where surface elevations are lower, the atmosphere is warmer, and melting persists. Positive reflectivity anomalies over the northwest ice sheet suggest the return and persistence of fresh snow.

Fig. 3. Daily albedo anomaly map.

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