ATMOSPHERIC CARBON DIOXIDE AND RADIOCARBON: II 



89 



LONG-LIVED 



LAND BIOTA 



Nu 



UPPER 



ATMOSPHERE 



N,, 



— 



LOWER 



ATMOSPHERE 



N, 



/ 4 ,(/ 7 ) 



SHORT-LIVED 



LAND BIOTA 



N 



OCEAN SURFACE 



LAYER 



N m 



— 



DEEP SEA 



Nh 



Fig. 1 Diagrammatic representation of the six-reservoir model of C0 2 ex- 

 change. Arrows represent die direction of fluxes hetvveen reservoirs. The N; 

 denote carbon masses for each reservoir. In the five-reservoir model (not 

 shown), the upper and lower atmosphere are combined to form a single 

 atmospheric reservoir. Transfer coefficients k; and l\ are defined in 

 Appendix C. 



more and more nations. Continued exponential growth probably will not be 

 limited by vanishing resources until well into the 21st century and possibly for 

 as long as another hundred years. Exponential growth typically continues until 

 nearly half of a natural resource is exhausted. 12 The ultimate production of 

 coal, petroleum, and natural gas, as estimated by Hubbert, 1 2 would release five 

 to nine times as much carbon as the preindustrial atmosphere contained. If 

 Hubbert's lower limit is correct, 4% per year growth is possible until about 2040. 

 Left out of Hubbert's estimates are the very large deposits of oil shales, which 

 contain several hundred times as much carbon as the preindustrial atmosphere. If 

 even a small portion of these is exploited, exponential growth may continue 

 considerably longer than indicated by Hubbert's upper limit, even as far into the 

 future as 2070, by which time a 4°b per year growth would have released into 

 the atmosphere C0 2 equivalent to eight times the preindustrial atmosphere level. 

 Industrial C0 2 production data used in this study are from an analysis by 

 Keeling 13 of data assembled by the United Nations for the period 1860 to 1969 

 (Fig. 2). For essentially all industrial C0 2 produced before 1860 to be included, 

 an exponential relation, derived from the data up to 1900, was extrapolated 



