ATMOSPHERIC CARBON DIOXIDE AND RADIOCARBON: II 



107 



r dm> i s set equal to 1500 years (to agree approximately with the observed ' 4 C/C 

 ratio of deep-ocean water). We find as best-fit values r am = 6.3 and |3 = 0.56. The 

 predicted Suess effect, Su 48 , is —1.99%. In the second model we increase 

 N m0 /N a0 to 4 and find as best-fit values r am = 7.0 and j3 = 0.44. The predicted 

 Su 4 8 in this case is —1.80%. We could, of course, choose more cases, but these 

 two are sufficient to illustrate the uncertainty in (5 and predicted Su 48 as 

 N m0 /N a0 is varied. 



PREDICTIONS 



If we assume the first preferred model and continued 4% annual increase in 

 fossil-fuel combustion and if the land biota is now assumed to increase in mass 

 according to the nonlinear equations Eqs. 2, 3, 5, and 6, the concentration of 

 atmospheric C0 2 will reach 6.0 times its preindustrial level by 2070 (Fig. 8 and 

 Table 3a). (The input is 8.00 Ni , the atmospheric fraction 62.5%; consequently 

 the atmospheric increase factor is 8.00 X 0.625 + 1 = 6.0.) If the ocean surface 

 layer is assumed to be twice as large (second model, Table 3b), the predicted 

 value is 6.3 (=8.00 X 0.664 +1). The first model implies that the biota almost 

 doubles in mass in the next 100 years. The second model predicts a 70% increase 

 in mass. 



Actually a large increase in biomass is unlikely to occur in the next century. 

 A rising demand for agricultural land and timber is almost sure to occur along 



800 



a 



B 600 



c 



CO 



< 



LU 



cc 

 u 



o 



400 



200 



1960 



1980 



2000 



2020 

 DATE 



2040 



2060 



Fig. 8 Predicted C0 2 increase in the atmosphere for the model with 



am 



6.27 vears, N 



mo 'Nao 



2, (3 = 0.556, and T^ m = 1500 years. Curve A is 



with the biota growth stopped (0 set to 0) in 1970; curve B is with no cutoff 

 of biota growth. 



