Correspondence of Greenland ice sheet reflectivity decrease with US annual energy consumption

Greenland ice sheet surface reflectively change for June is characterized by a 6% decline between years 2000 and 2012 (Fig. 1). Considering the average all-sky (clear and cloudy) solar receipt of 360+/-20 Watts per square meter of area (see Box et al. 2012), it is elementary to conclude that the ice sheet absorbed an additional 1020 Joules (1 Joule is a Watt per second) or 100 Exajoules more solar energy. According to the International Energy Agency, this monthly figure eclipses the annual energy consumption for the United States in year 2011 (91 Exajoules).

Fig. 1. June albedo time series for the Greenland ice sheet.

The reflectivity change for July is -7% for the 13 summers spanning 2000-2012. Similarly, the ice sheet absorbed another additional 120 EJ of energy in July 2012 as compared to July 2000. This energy is disposed by some combination of melting and perhaps more importantly in the raising of the temperature of the ice and snowpack on Greenland. Box et al. (2012) calculate that the 2000-2011 additional 148 EJ solar energy absorption from June-August is sufficient to completely erode the “cold content” of the 1.494106 km2 accumulation area to a depth of 14 cm, assuming its temperature, density, and specific heat to be -10 deg. C, 360 kg m/3, and 2110 J/kg/K, respectively. An important implication is that less energy will be required in future melt seasons to bring snowpack to the melting point. Earlier onset of melt is likely. As such, the albedo feedback can operate more strongly, amplifying the impact of warming on melt.

Fig. 2. July albedo time series for the Greenland ice sheet.

Notes

  • See Box et al. 2012, Fig. 2 and related discussion for the accuracy of downward solar irradiance.
  • The albedo data are according to the MODIS MOD10A1 product and are cross validated in Box et al. (2012).

Work Cited

  • Box, J. E., Fettweis, X., Stroeve, J. C., Tedesco, M., Hall, D. K., and Steffen, K.: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012. open access
  • World Energy Statistics 2011, International Energy Agency, .pdf

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