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and deglaciation. A comprehensive well-funded effort, however, 

 is still not on the research agenda of any federal agency. 



CHANGES IN VOLCANIC AEROSOLS AND SOLAR IRRADIATION COULD 

 INFLUENCE CLIMATE 



From decade to decade solar irradiation and volcanic 



aerosols in the atmosphere may vary. An increase in aerosols 



can have a cooling effect, while an increase in solar irradiation 



will have a warming effect. In coming decades it is likely 



that there will be fluctuations for both factors, but there is 



no reason to expect a consistent long-range trend. Nevertheless, 



to test the possible influence of a strong shift in these 



factors, these changes were examined: 



o For the minimum case , we assumed high volcanic 



activity and a reduction in solar radiation. A level 

 of optical thickness was chosen that was five times 

 the historical average over the last 80 years. 24/ 

 A linear trend equal to a 0.5 percent reduction in 

 solar radiation by 2100 was assumed . 25/ 



o For the maximum case , we assumed solar irradiation 



increased by a linear trend to a 0.5 percent increase 

 by 2100, with no change in volcanic activity. 



o For the high volcanic case , we assumed high volcanic 

 activity, but no change in the solar constant. 



These and other special-case scenarios are reported in 

 Appendix A. They suggest that the greenhouse effect is not 

 likely to be overwhelmed by volcanoes or changes in solar 

 irradiation. 



