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THE ORNL CARBON CYCLE MODEL 



The Oak Ridge National Laboratory carbon cycle model repre- 

 sents flows and stocks of carbon on a global scale. V Terrestrial 

 carbon is modeled in considerable detail, while ocean carbon is 

 represented by a simple box-diffusion model. A general overview 

 of the model is presented here. 



Figure B-5 depicts the overall structure of the model. 

 Carbon in living material is divided between ground vegetation, 

 the wood parts of trees, and the non-wood parts of trees. Dead 

 organic matter is divided between detritus/decomposer and active 

 soil carbon. Finally, carbon in the oceans is subdivided into 

 surface (less than 260 meters below sea level) and deep layers. 



For each of the carbon reservoirs, equations specify maximum 

 stocks of carbon and rates of flow into and out of the reservoirs. 

 In general, terrestrial flows are modeled as linearly dependent 

 on carbon content of the i th donor reservoir (F^- = a^- C^ ) or as 

 a more complicated logistics function. (Details of the structural 

 equations can be found in Emanuel, et al., 1981.) 



The logistic functions for trees include terms for carbon 

 release to the atmosphere from forest clearing. Permanent forest 

 clearing is reflected by reductions in the parameters governing 

 storage capacity. Where clearing is temporary, reestablishment 

 of forests occurs in a delayed exponential fashion. (No future 

 clearing option was assumed in this study.) 



