- 104 - 



d 



dt [(SNOW + ICE) * T * SHI] = ENET + EMANDC . 



The time derivative was not calculated but is several orders 



of magnitude smaller than ENET or EMANDC. 



Sources of Error 



The results of the model should be interpreted in light of 

 the following sources of error: 



1 . The major source of error is that the climate model uses 

 fractional grid, i.e., each grid box can can contain ocean, 

 sea ice, land ice, and earth. The composite surface 

 albedo is an area-weighted average of the albedos of the 

 separate surface types, but once the composite surface 

 solar absorption is calculated, it is distributed into 



the surface types uniformly. When ocean ice is replaced 

 by open ocean, the composite albedo will decrease and the 

 increased solar absorption should primarily go into the ocean. 

 However, the model erroneously sends part of the absorbed solar 

 energy into the land ice and ocean ice. Correction of this 

 feature of the model could significantly decrease the estimated 

 melting rate of glaciers. 



2. Another aspect of the fractional grid is that sensible heating 

 is proportional to the ground temperature minus the surface 

 air temperature, but the air temperature is a composite of the 

 entire grid box. Because land ice is at a higher altitude than 

 sea ice and the ocean, the sensible heating over land ice is 

 underestimated in both runs. Because the net melting is the 



