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new technologies might be developed that vastly reduce the costs 

 of extracting hydrocarbons from shale or tar sand; or nuclear 

 fusion might become a commercial reality sooner than expected. 

 Any of these "surprises" would alter fuel use and emissions in 

 ways unanticipated by our analysis. Although counting on such 

 surprises would be foolish for a study like this, our conclusions 

 must be tempered by the realization that the future may be very 

 different from the extensive range of possibilities currently 

 envisioned as possible. 



With respect to the scenarios generated, the assumption that 

 nuclear energy costs could be instantaneously halved in 1980 is 

 overly optimistic. It was used simply to test the implications 

 of a radical shift in the cost of a major energy source that does 

 not emit CO2 . Other experiments with the model, such as doubling 

 or tripling the cost of fossil fuels, had negligible effects on 

 atmospheric temperatures.^/ 



Although the IEA energy model was designed for long-range policy 

 analysis and satisfies this overriding objective, it does not con- 

 sider the capital constraints that may limit the rates of substi- 

 tution among competing fuels. By ignoring potential bottlenecks 

 that could result, the model tends to overestimate the degree 

 to which rapid change in energy supplies is possible. However, 

 since the results of this study (projections of sea level rise) 

 were relatively insensitive to energy projections, this limitation 

 of the IEA model is not critical. 



