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Predicting Snow and Ice Contribution Using Climate Models 

 The most comprehensive tool for understanding climatic 

 change is the three-dimensional general circulation model 

 (GCM). By solving a series of equations that represent the 

 fundamental laws of atmospheric structure and motion, such 

 models simulate the earth's weather on an hour-by-hour basis, 

 moving moisture and heat upwards and downwards, north and south, 

 east and west. Although the models represent the actual atmos- 

 phere, solar irradiation, and the reflectivity of the earth with 

 a fair degree of accuracy, the topography used is coarse; 

 variations in large geographic regions are averaged together, 

 and each grid is treated as a plateau. 



By accumulating hourly and then daily weather statistics, 

 these models can generate years of data that represent the 

 climate of different regions. Since the models do not yet 

 represent all of the processes that determine climate, one 

 finds some discrepencies. Nevertheless, in most aspects, a 

 GCM simulates weather fronts realistically: rain, snow, heat 

 and cold are generated by the same mechanisms active in the 

 actual climate system. By comparing projections of these 

 models (assuming today's CO2 levels) against observed weather 

 and climate, GCMs ahve been shown to accurately reproduce 

 the world's weather patterns. 



