28 MACHTA 



inhibits turbulent transfer of heat. Further, C0 2 in the air always cools the 

 atmosphere, but more C0 2 cools the lower atmosphere less while cooling the 

 high atmosphere more. 



The response of the atmosphere to changes in the radiation distribution is 

 very complex, and a fully evolved model to simulate the climatic change does 

 not now exist. What can be reported are only approximations to the true 

 atmospheric adjustment to increasing C0 2 concentrations. Radiative transfer 

 theory is reasonably well established. But the dynamic responses, air movements 

 and energy transfers, are much more difficult to recreate. Perhaps most 

 important, the changes in cloudiness that represent a dominant influence on the 

 global heat budget may be modified in a manner as yet unpredictable. 



The Manabe and Wetherald 6 study is most often quoted as the best one 

 currently available on the change in temperatures from the addition of C0 2 

 from a one-dimensional (vertical) model. Figure 5 shows the relation between 

 atmospheric C0 2 content in parts per million to change in global surface 

 temperature away from the current 320 ppM. The prediction of 385 ppM in the 

 year 2000 calls for a warming of about 0.5°C. A slightly different radiative 

 treatment reduces the warming by about 30%. The model on which this forecast 

 is based allows for new radiative temperature changes for increasing C0 2 but a 

 constant relative humidity to try to cope with the added moisture that warmer 

 air can hold. However, the average cloudiness employed in the calculations does 

 not change when the air warms or cools. The model also produces much greater 

 cooling in the high atmosphere than warming near the ground. 



Manabe 7 has recently reported on some calculations using a three- 

 dimensional model comparing climatic conditions with a doubling of the current 

 C0 2 atmospheric composition. No ocean circulation is admitted, and a perpetual 

 winter is prescribed. Further, there is still no change in the cloudiness even when 

 the atmospheric humidity changes in response to the heating by the added C0 2 . 

 The result suggests a slightly greater global warming in the lower atmosphere 

 than Manabe and Wetherald found in their one-dimensional case. But most 

 dramatic is the much larger warming of the Arctic than might have been 

 expected. The high latitudes warm twice as much as the globe as a whole. This is 

 due to the marked thermal stability of the Arctic lower atmosphere in winter 

 and the recession of the ice with the added warmth of the air. This calculation 

 should not be treated literally but is suggestive of the fragility of the Arctic 

 region to climate changes. 



Indeed the cooling that has been in progress since the mid-1 940s in the 

 Northern Hemisphere has been concentrated almost entirely in the Arctic (north 

 of 50°) and in the winter half-year. This cooling has proceeded despite the rapid 

 increase in C0 2 evident in the atmospheric concentration. One must recognize 

 that other factors besides C0 2 are responsible for the global climate; in all 

 likelihood natural fluctuations, as yet not understood, play a dominant role 

 since climatic fluctuations occurred long before man had his present technologi- 

 cal powers and numbers. 



