76 H. D. MACGINITIE 



the Paleozoic limestone beds, but what brought the return of the 

 mild climates in the Mesozoic? As far as we know now, the only 

 source of carbon dioxide in any quantity is volcanism. Yet intense 

 and long-continued volcanism seems to precede rather than follow 

 Glacial ages. 



Carbon dioxide is more soluble in cold water than in warm. The 

 present cold oceans are a storehouse for incredible amounts of CO2. 

 If the climate should become warmer, large amounts of the gas would 

 be released to the atmosphere. But here we see that an increase of 

 carbon dioxide is an effect of, rather than the cause of, warmer 

 climate. Warmer climates also mean an increase in the total amount 

 of water vapor in the atmosphere. There is little question that 

 changes in the concentrations of these gases tend to emphasize 

 climatic fluctuations. The role of continentality in initiating or 

 terminating Glacial ages has been greatly overemphasized. No 

 known distribution of land and water and no known variations in 

 topography are adequate to account for the changes in climate 

 since the Upper Cretaceous. Anyone who is familiar with the cli- 

 matic change in the central United States between the spring of 

 1956 and the spring of 1957 must be aware that some other efifect 

 than size, shape, and topographic relief of the continents must be 

 the cause of major changes in circulation patterns. Terrestrial factors 

 are capable of increasing climatic contrasts and channeling currents 

 of air and water, but they cannot, on the basis of our present knowl- 

 edge, affect the climate of the earth as a whole (Willett, 1953, pp. 

 58-59). The solution of the problem of changing climates is not to 

 be found in the theories of wandering poles and drifting continents. 

 Any forms of these theories yet developed directly contradict the 

 known facts concerning the distribution of fossil floras. In addition 

 to the negative biologic evidence there is also direct physical evidence 

 against the idea of wandering poles. From his study of the orientation 

 of magnetic grains in sediments, Hospers (1955) has "concluded 

 that the large amount of polar wandering suggested by Kreichgauer, 

 Koppen and Wegner, and Milankovitch cannot be reconciled with 

 the new data. If ... at all ... it ha& not exceeded 5°-10° since 

 Eocene times." 



The evidence of a recent warming of world climate is clear. If the 

 present trend toward warming and drying continues, our south- 

 western deserts will eventually expand into Oklahoma, Texas, and 



