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Finally, methane is also assumed to grow: ^0/ 



o The low scenario assumed 1.0 percent growth per year. 



o The mid-range scenario assumed 1.5 percent growth per 

 year. 



o The high scenario assumed 2.0 percent growth per year. 



Our analysis did not consider changes in ozone concentra- 

 tions at different altitudes, which may prove to be important. 

 Ozone depletion in the upper stratosphere caused by chlorofluro- 

 carbon emissions will tend to have a warming effect because 

 the loss of ozones' infrared absorbing capibility at this 

 altitude will be more than offset by the additional U-V energy 

 allowed to penetrate to the earth's surface. Higher ozone 

 levels in the lower stratosphere and upper troposphere, caused 

 by NO x emissions from airplanes, will cause additional warming 

 because at those altitudes the additional infrared that is 

 absorbed outweighs the reduction in ultraviolet that penetrates 

 to the surface . ' other minor greenhouse gases, such as CCl^, 

 CF 4 , NH3, and C2CI3F3 (CFC-113) could also contribute to the 

 warming, but were not considered in this analysis. 



Climatic Responses 



As the atmospheric abundance of gases that absorb infrared 

 radiation increases, the earth's temperature will rise. The 

 extent of the ultimate warming will depend on how much the 

 initial warming alters the levels of other infrared-absorbing 

 gases such as water vapor, or its reflectivity, by changing 

 ice and cloud cover. 12/ These "feedbacks" may amplify the 



