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Projections of the concentrations of chlorof luorocarbons 



and other trace gases involved much less sophistication than 



our projections of CO2 concentrations.^' 



o The low scenario assumed that emissions of chloro- 

 f luorocarbons grew at 0.7 percent of the 1980 level 

 (1.8 million kg) annually until being capped in 2020 

 and that CFCI3 (CFC-11) and CF 2 C1 2 (CFC-12) have 

 half-lives of 60 and 120 years, respectively. 



o The mid-range scenario assumed that emmissions of 



CFCI3 and CF2CI2 grew at 2.5 percent of the 1980 level 

 (6.4 million kg) per year until 2020 and then are 

 capped . 



o The high scenario assumed that emissions of CFCI3 

 and CF2CI2 grew at 3.8 percent of the 1980 level 

 (9.8 million kg) per year until being capped in 2020. 



The low assumption implies that atmospheric concentrations 



will gradually approach an eguilibrium concentration by 2100. 



Although the high assumption implies that concentrations will 



grow faster, it is not really an upper bound for likely future 



concentrations. It is possible that chlorof luorocarbon 



emissions will never be capped, or that their use in developing 



countries will parallel that of the developed countries 



(a growth not anticipated in tne high scenario). 



Nitrous oxide concentrations are also assumed to increase: V 



o The low scenario assumed 0.2 percent per year growth. 



o The mid-range scenario assumed 0.45 percent per year 

 growth. 



o The high scenario assumed 0.7 percent per year growth. 



