112 BACASTOW AND KEELING 



£, defined in Eq. 1, because it expresses the immediate pressure response of the 

 water to added C0 2 , whereas £ expresses the slowly varying average response 

 since preindustrial times. Given continued 4% annual increase in fossil-fuel 

 combustion, the model predicts that £ will increase more than 10-fold in the 

 next century. In consequence of this increase not more than 6% of the industrial 

 C0 2 produced in 2070 will enter the oceans that same year whether the biomass 

 remains static or grows in size. 



HELIOMAGNETIC EFFECT OIM RADIOCARBON PRODUCTION 



In the preceding calculations of the six-reservoir model, we assumed a 

 variable production of radiocarbon in the stratosphere, as provided by 

 Lingenfelter's I4 C production equations, 41 and the annual sunspot record after 

 1500 (Fig. 9, Appendix F). The results of the calculations are compared in 

 Fig. 10 with a similar calculation ignoring the possible sunspot effect. The 

 predicted fluctuations are small (as anticipated in the preceding paper, Ekdahl 

 and Keeling, 7 and would be hard to detect, given the scatter in the present data 

 (see Fig. 11). The agreement is not nearly so good as Grey and Damon 42 found 

 (Fig. 12 of the preceding paper, Ekdahl and Keeling 7 ) after adjusting their single 

 exchange time. Our results indicate a negligible correction (—0.03%) needs to be 

 added to the Suess effect parameter Su 48 . The correction for 1954 is only 

 slightly greater (-0.09%). Of course, it is possible that the Lingenfelter equation 

 underestimates the heliomagnetic effect upon 14 C production and that larger 

 corrections should be applied. 



The time-varying atmospheric 14 C/C ratio, its correlation with sunspots, and 

 the Suess effect could be better understood if we had high-quality tree-ring data 

 for the entire period after 1750. Houtermans et al. 18 and Lerman et al. 20 have 

 demonstrated that high-quality data can be obtained by existing techniques. 

 Such data would add to our confidence in modeling l 4 C variations and hence to 

 our understanding of the carbon cycle. 



SUMMARY AND CONCLUSIONS 



In a search for a reasonable prediction of changes in atmospheric C0 2 

 concentration over the next 100 years, we have explored the relationships 

 between parameters of a six-reservoir geochemical model and observable 

 quantities. The increase in atmospheric C0 2 concentration over approximately 

 the past 10 years establishes the fraction of industrial C0 2 recently remaining 

 airborne but offers no clue as to whether the remaining industrial C0 2 has 

 entered the oceans or has been incorporated in land plants. We initially hoped to 

 use measurements of radiocarbon to establish the fraction that enters the oceans, 

 and we were encouraged to find that the model predicted the industrial dilution 

 of atmospheric radiocarbon (the Suess effect) within the experimental accuracy 



