SALINITY LOWERS THE FREEZING POINT 431 



temperature, its capacity for holding COo in solution would be sufficiently 

 reduced so that it would give up enough of its abundant supplies of this 

 gas to the air to double the present atmospheric amount. The climatic 

 significance of atmospheric COg, while probably not as great as some have 

 tliought likely, nevertheless certainly is appreciable. Even Humphreys" 

 admits tliat a doubling or halving of the COo content of tlu' air would 

 ])roduce directly a temperature change of about one-fifth of that esti- 

 mated to have occurred since the height of glaciation. The indirect 

 effects of changed CO, content of the air are certainly greater than the 

 direct. 



A second indirect effect of the lower freezing point produced by in- 

 creased salinity also springs from the fact that less of the sea is ice-cov- 

 ered, but it depends on the effect of the ice on air temperatures instead 

 of on water temperatures. When the sea is ice-covered it gives up ])rac- 

 tically no Ireat to tlie air and becomes, to all intents and purj^ises, a land 

 surfac-e. x\s a result, continents bordered by an ice-covered sea liecomo 

 niucli colder in winter than lands bordered by an open sea. This is due 

 not ()]ily to their receiving less heat, but because they lose far more quickly 

 wliatever heat they may have left from the supply received from the sun 

 tlie preceding autumn. When the Avind blows from an open ocean in 

 winter it causes a fog and clouds on the adjacent lands, and these hold 

 in the lieat. If a coast is ice-bound, the belt of fog and cloud is pushed 

 seaward, and the cloudiness on the continent diminishes and the heat is 

 radiated away far more quickly than wlien the sky is cloud-covered. 

 With decreased cloudiness, snowfall would decrease on the lands. The 

 sunnners of the Arctic Ocean are now kept exceptionally cold by the snow- 

 mantled ice, with its great reflection of sunlight and its large absorption 

 of iieat in melting. 



Furthermore, because of the low temperatures, anticyclonic conditions 

 prevail, with the result that the winds usually blow radially outward 

 from the ice-covered portions.* When the oceans were fresher than noAv, 

 this effect must have been magnified, with a consequent diminution of 

 polar and subpolar snowfall in summer as well as winter. Tliis means 

 that under given conditions of temperature, land distribution, and so 

 fortli, tlie ice-covered portion of the ocean was greater, and hence the 

 possibilities of precipitation at high latitudes were less with the less 



■■'■ W. .T. Hiimphre.vs : I'liysics of the air, 1020, p. 607. 



^ r. E. p. Brooks : The meteorological conditions of an ice-sheet and their hearing on 



the desiccation of the globe. Quart. .Touru. Royal Meteorol. Soc. vol. xl, 1014. pp. .")8-7(>. 



W. II. 1-Iobhs : Characteristics of existing glaciers. 1011. The role of the glacial 



anticyclone in tlie air circulation of the globe. Proc. Am. Phil. Soc, vol. liv. 101."i, ]i|i. 



