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Even the ORNL carbon cycle moael, however, is oversimpli- 

 fied, representing the oceans as a layered vertical column or box, 

 and the biosphere by only a few types of vegetation. Ocean dynamics 

 are far more complex, containing complicated and interdependent 

 vertical and horizontal transports. Ocean chemistry is not well 

 represented in models of the carbon cycle, and sources and sinks 

 may be over- or underestimated. 



The impacts of CO2 and temperature change on photosynthesis 

 and changes in ecosystems are not considered by these models. 

 The inaccuracies produced by such emissions have not been estimated. 



INCREASES IN CONCENTRATIONS OF TRACE GASES 



Increases in the concentrations of trace gases will add 

 significantly to the warming from CO2. This report considers 

 four of the most important gases: methane, nitrous oxide, CF2CI2 

 (CFC-12), and CFCI3 (CFC-11). 



Scientific knowledge- of these gases is sufficient to separately 

 project emissions and atmospheric residence time only for chloro- 

 f luorocarbons . We assume that the half-lives of CFCI3 and CF2CI2 

 will be 60 and 120 years, respectively. The low, mid-range, and 

 high scenarios assume that emissions will increase annually by 

 0.7, 2.5, and 3.8 percent of the 1980 level until 2020. Because 

 these emissions will also cause depletion of stratospheric ozone, 

 we assume that additional restrictions will be placed on their use 

 and that emissions will remain constant after 2020. Because of 

 the long residence times for these gases, their concentrations 



