TEMPERATURE OF THE ATMOSPHERE 29 



Plants need less light as the temperature rises, and more as it 

 falls. 



TEMPERATURE OF THE ATMOSPHERE. 



The chief source of atmospheric heat is the sun. while of much 

 less significance is the internal heat of the earth. Other local 

 causes, such as friction in landslides, etc., volcanic activities, fires, 

 organic decay, -etc., and movements of the atmosphere itself, locally 

 warm the air, but these are generally of almost negligible signifi- 

 cance. 



The amount of heat received by the earth from the sun each 

 year would, if equally distributed, melt a layer of ice about 141 feet 

 thick over the entire surface of the earth, or evaporate a layer of 

 water 18 feet deep; yet the amount received is less than 1/2,000,- 

 000,000 of the heat given ofif by the sun. The space outside of our 

 atmosphere is believed to have a temperature of — 2^]^° C. 

 ( — 459° F.), which would be the winter temperature (coldest 

 month) of the polar regions of the earth if there were no at- 

 mosphere. The winter temperature of the equator would be about 

 + 56° C. (-(-164.8° F.). The estimated summer temperature at 

 the poles under the same condition would be +82° C. ( +21 1.6° F.), 

 while that at the equator at the same time would be only +67° C. 

 (-|- 184.6 F.), since the polar regions, owing to their continuous day 

 in summer, would receive a greater amount of total heat. The 

 minimum observed temperature is — 60° C. and the maximum 

 -|- 80° C. The chief agents in retaining the sun's heat within the 

 earth's atmosphere are the carbon dioxide and the water vapor, 

 which act as thermal blankets. It has been estimated by Arrhenius 

 (2) that if the amount of COo in the atmosphere were in- 

 creased 2.5 to 3 times its present value, the temperature in the 

 arctic regions must rise 8° to 0° C. and produce a climate as mild 

 as that of Eocenic time, so that magnolias would again grow in 

 Greenland. On the other hand, if the CO, were decreased to an 

 amount ranging from 0.62 to 0.55 of its present value, a fall of 

 from 4° to 5° C. would result and glacial conditions would again 

 overspread the northern parts of the continents. These estimates 

 have been seriously questioned, but the general fact that both COj 

 and water vapor act as thermal blankets is established. Chamber- 

 lin (13, 14, 15) has discussed in detail the bearing of these facts 

 on former continental glaciation. his argument being that the ab- 

 straction of the COo from the atmosphere during the periods of ex- 

 tensive vegetal growth, i. c, the periods of coal formation, tended 



