PREDICTION OF C0 2 IN THE ATMOSPHERE 23 



Charlie and in the western United States, 2 support the trends on Fig. 1, the 

 mean monthly carbon dioxide concentrations at Mauna Loa. There are two very 

 obvious features in this figure. The first is a long-term increase and the second a 

 strong seasonal variation. It is the long-term increase projected into the future 

 that will be discussed. Between the period 1958 and 1971, the growth of C0 2 in 

 the air is about one-half that put into the air by the fossil-fuel C0 2 if it is 

 uniformly distributed throughout the atmosphere. The other half has gone into 

 the biosphere or into the oceans. The prediction of this partitioning into the 

 other reservoirs is needed to forecast future CO-, concentrations. 



THE MODEL 



Figure 2 shows the model used. It contains a troposphere, a stratosphere, a 

 mixed layer and a deep layer of the ocean, a long-term biosphere, a short-term 

 biosphere, and a marine biosphere. The exchange between atmosphere and ocean 

 is based on first-order kinetics, whereas the uptake of carbon by each biosphere 

 is the net primary production (NPP). I am indebted to Jerry Olson (Oak Ridge 

 National Laboratory) and George Woodwell (Brookhaven National Laboratory) 

 for most of the details of the biosphere, but I, rather than they, must take the 

 blame for any of the inaccuracies. The exchange between stratosphere and 

 troposphere is based on the fact that radioactive material in the stratosphere has 

 a residence time of about 2 years. The exchange between the deep and mixed 

 layers of the ocean is based on the fact that the average age of the carbon in the 

 deep ocean is about 1600 years. The values for the NPP are taken either from 

 the estimates that were given to me by Woodwell and Olson or from Lieth. The 

 last and most important exchange is that between the atmosphere and the mixed 

 layer of the ocean which is based on the l C0 2 from nuclear tests. 



Figure 3 shows the time history of 14 C atoms produced by nuclear tests in 

 the troposphere and in the entire atmosphere to about 30 km as derived from 

 data collected by the U. S. Atomic Fnergy Commission mainly over North and 

 South America. The sharp increases of these curves reflect periods with active 

 testing. After about 1963 there were only a few injections into the atmosphere, 

 and small corrections have been made for these. 



After about 1963 the 14 C0 2 content of the entire atmosphere decreased. 

 This fact implies that there has been a transfer to other reservoirs, into either the 

 ocean or the biosphere. We have specified the transfer into the biosphere; hence 

 the remaining atmospheric decrease must be the result of CO? entering the 

 oceans. This reasoning and Fig. 2 form the basis for the exchange coefficient 

 between the atmosphere and the ocean, using a trial and error procedure. The 

 mean residence time in the atmosphere for a C0 2 molecule becomes about 

 5 years. The trial and error procedure also provides a mean residence time ot 

 carbon and the carbon content of the mixed layer of the ocean. This carbon 

 content corresponds to the depth of the mixed layer of 110 m. It represents the 



