PREDICTION OF C0 2 IN THE ATMOSPHERE 27 



within ±10 ppM, which is not significant in the light of the uncertainties (to be 

 discussed in the following paragraphs) of converting the C0 2 predicted 

 concentration into a climatic forecast. 



However, these sensitivity tests of changes in the model reflect but the tip of 

 the iceberg of uncertainty in predicting future levels of C0 2 . It is naively 

 assumed in these tests that the history of the atmosphere— biosphere— ocean 

 transfers found in the 1950s and 1960s have and will be applicable from 1860 to 

 2000. This is hardly likely to be the case. In fact, year-to-year differences exist 

 between the simple-model predictions and the Mauna Loa observations. Put 

 another way, the model presumes, in effect, that about 60 to 65% of the 

 fossil-fuel C0 2 will remain airborne each year. But in the mid-1960s this 

 observed percentage dipped below 40 and, in very recent years, rose to well over 

 60, assuming that the Mauna Loa annual increments are representative of those 

 for the globe. If these changes in the airborne percentage are indeed valid, there 

 are significant year-to-year changes in the uptake by the biosphere and oceans. 



To more clearly make this point, we compare the C0 2 photosynthetic 

 uptake with fossil-fuel emissions. From Fig. 2, there are 5.6 or 7.6 X 10 16 g of 

 carbon taken up (and presumably released by respiration and decay) each year, 

 depending on whether we want to include the very uncertain marine NPP. This is 

 about 15 to 20 times greater than the 1969 fossil-fuel C0 2 releases. Thus a 1% 

 decrease in the photosynthetic uptake due to droughts or other factors would 

 appear as a 15 to 20% increase in the airborne fossil-fuel C0 2 . Do we know that 

 the year-to-year values of global NPP will not change by 1%? 



Assuming that the atmosphere comes into equilibrium with the sea-surface 

 partial pressure of C0 2 , we can argue that each 1 C warming of the ocean 

 surface will increase the C0 2 content by as much as 10 ppM. A global warming 

 of the ocean temperature of only 0.1 C could possibly equal the current annual 

 increment of C0 2 in the air. 



These comparisons suggest strongly that the biosphere and oceans play so 

 vital a role in the changes in atmospheric C0 2 content that small changes in their 

 behavior can easily modify the predictions from the simple model calibrated 

 from conditions in the 1950s and 1960s. 



CLIMATE PREDICTION 



An even larger measure of uncertainty must be attached to the prediction of 

 climatic changes from an increase in atmospheric C0 2 . It is well known that 

 C0 2 absorbs short-wave solar wavelengths poorly but long-wave terrestrial 

 wavelengths effectively. Thus solar radiation can reach the earth unattenuated 

 by any increase in C0 2 concentrations, but the long-wave terrestrial radiation 

 will be absorbed and partly emitted back to the lower atmosphere. The result is 

 the greenhouse effect. But the analogy between an atmosphere with enhanced 

 absorbers of long-wave radiation and a greenhouse is not good, because the glass 



