580 E. HUNTINGTON SOLAR PIYPOTHESIS OF CLIMATIC CHANGES 



and is largely lost, so far as any effect on the eartli^s surface is concerned. 

 Hence it appears that the greater the amount of evaporation from the 

 ocean, the greater will be the amount of heat carried to high levels antL 

 the greater will be the cooling effect on the earth's surface. 



THE EFFECT OF A PER 21 1 AX CLOUD BLANKET IX LOW LATITUDES 



We must now consider the extent to which an increase in atmospheric 

 moisture and cloudiness in subtropical and equatorial regions would ex- 

 ercise a blanketing effect which might neutralize the cooling effect de- 

 scribed in the last paragraph. As every one knows, on clear nights frost 

 is much more probable than on cloudy nights. AYlien the air is full of 

 moisture, and especially when it is cloudy, the earth's heat is not radiated 

 away so fast as when the air is clear and dry. The universality of this 

 phenomenon raises tlie question whether under conditions such as we 

 have postulated during Permian times the great abundance of clouds 

 might not actually cause the temperature of the earth's surface to rise 

 rather than fall. To put the matter concretely, we must find the relation 

 between two types of processes. On the one hand, we have the cooling 

 processes. These are three in number : First, the convective carrying 

 away of heat from the earth's surface by reason of rapid cyclonic circu- 

 lation ; 'second, the carrying away of heat because of rapid evaporation, 

 and third, the actual loss of heat which would arise from the reflection 

 of the sun's rays from the upper surface of the clouds. This last factor 

 has not hitherto been mentioned, but it plays an important part. Water, 

 as is well known, possesses a high reflective power, and the same is true 

 of clouds. If any part of the earth's surface is shrouded with clouds, 

 there must be a corresponding absolute loss in tlie amount of heat re- 

 ceived from the sun. 



In opposition to the three cooling processes there seems to be only one 

 heating process which would play any important part under the condi- 

 tions of the cyclonic hypothesis. Inasmuch as the wave length of sun- 

 light is very short, solar energy, unless it is reflected from the surface of 

 clouds or of other reflecting media, is able to pass through masses of 

 vapor without being absorbed to any great extent. On reaching the 

 earth, however, it is converted into heat and is sent out from the earth's 

 surface in this form. The wave length of heat is great. Hence when 

 the waves come into contact with vapor they can not easily pass through 

 it, but are largely absorbed. For this reason clouds prevent the earth 

 from becoming cool. 



Our problem is to determine whether, under the conditions of our 

 hypothesis, the loss of heat in Permian times on account of increased 



