- •30 - 



Accurate estimation of the partial deglaciation of the 



West Antarctic, East Antarctic, and Greenland ice sheets for 



the next 120 years will require detailed studies of the specific 



ice sheets. Such studies should consider such factors as the 



predicted temperature of the upper surface of the ice, surface 



precipitation rates, ocean water temperatures, melting of ice 



shelves from the bottom, speeds of ocean currents and their 



ability to remove ice, the specific topography of the "gates" 



(narrow areas that constrict the flow of ice), and the specific 



location of grounding lines (land on which marine ice sheets 



rest ) . 20/ These factors will determine the speed of discharges. 



Unfortunately, such studies have not yet been made for deglaciation 



in the next century. 



Method Used to Estimate Snow and Ice Transfers from Land 

 to Sea 



In the absence of appropriate studies of the various ice 



fields, another approach had to be used that was much less 



direct : 



o A range of historic sea level rise estimates was 

 gathered from the literature. 



o An estimate of the historical sea level rise 



attributable to thermal expansion of the oceans was 

 obtained from the literature. 



o High and low ratios of ice and snow contributions to 



thermal expansion were computed using different estimates 

 of the historical sea level rise with the single estimate 

 of past thermal expansion. 



o These ratios were assumed to remain constant in the future 

 (implying that snow and ice contributions will proceed 

 in marginal steps and that deglaciation, when averaged 

 across all ice sheets, will also be a proportional 

 phenomenon) . 



