116 BACASTOW AND KEELING 



measurable correlation with sunspots actually exists. We are aware that a major 

 laboratory effort is required. Our model predictions, we hope, may provide 

 motivation for intensifying the effort already begun. 



As for the prediction of atmospheric C0 2 increase in the next century, the 

 nonlinear C0 2 transfer equations for seawater indicate unambiguously that the 

 world oceans will become progressively less able to absorb new increments of 

 industrial C0 2 , regardless of whether the oceans absorbed much or little 

 industrial C0 2 in the past. Understanding ocean behavior is, however, only half 

 the problem; for a valid prediction we also need to know whether the biomass of 

 land plants will change in the next century. In our model we assume that the 

 land biota responds to gaseous C0 2 approximately as do individual plants grown 

 in glasshouses with adequate light, water, and nutrients. If this assumption holds, 

 the land biomass (including detritus) may nearly double by 2070. More likely, 

 however, the biota, as well as the oceans, will be less and less able to absorb new 

 increments of industrial C0 2 because of competition between plants and 

 changing land use by man. But, even if the conditions for land biomass increase 

 are optimum, plant growth will not be able to keep pace with a rising rate of 

 consumption of fossil fuels. If present industrial trends continue, the concentra- 

 tion of atmospheric C0 2 will rise to at least six times its preindustrial level 

 during the next hundred years. If the biota does not respond appreciably to 

 higher C0 2 concentrations in the air, the rise may be to over eight times the 

 preindustrial level. 



ACKNOWLEDGMENTS 



This study was initiated while Charles Keeling was a participant at the Study 

 of Critical Environmental Problems, July 1969, in Williamstown, Mass. We are 

 indebted to J. B. Hilmon, Lester Machta, Jerry Olson, Roger Revelle, 

 Frederick E. Smith, and George M. Woodwell for discussions in Williamstown 

 which assisted us in formulating our general model, especially the division of the 

 land biota into two reservoirs. We are also indebted to Wilhelm Mook and 

 Johann Vogel for advice on the radiocarbon problem, and to Jonathan Machta 

 for help in devising preliminary numerical methods involving an increasing land 

 biota. We thank Peter Guenther and Alex Adams for help in carrying out the 

 computations. The authors are also indebted to Anne Thistle for special help in 

 preparing the manuscript. 



The work reported was supported by the Atmospheric Sciences Division of 

 the National Science Foundation under grant GA-31324X. 



REFERENCES 



1. Inadvertent Climate Modification, report of the Study of Man's Impact on the Climate 

 (SMIC), The M.I.T. Press, Cambridge, Mass., 1971. 



