242 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



While Newcomb's conclusion as to the change of temperature between the times of 

 maximum and minimum sun-spots rests upon unassailable evidence, his last conclusion as 

 to the relation of the changes to meteorological phenomena is based purely on inference 

 and is open to question. He has failed to consider the effect which even a slight change of 

 temperature may have upon meteorological conditions provided it be permanent. In his 

 11-year cycle the range of temperature is 0.26° C. In order to estimate the true importance 

 of such a variation, it is necessary to consider what would be the result if the temperature 

 no longer fluctuated back and forth between the two extremes every eleven years, but 

 remained constant at one extreme for a few centuries and then at the other for a corre- 

 sponding length of time. 



In order to explain the glacial period, geologists and students of " paleo-meteorology " 

 postulate a change of the mean temperature of the earth's atmosphere many times larger 

 than Newcomb's change in the 11-year cycle, but not of a different order of magnitude. 

 Penck, the leachng German student of glaciation, believes that a permanent change of 

 5° C. is sufficient to account for the difference between the conditions of the glacial period 

 and those of to-day. According to Ekholm, a lowering of the mean annual temperature 

 to the extent of from 7° to 9° C. would cause the snow-Une of the earth as a whole to descend 

 3,300 feet, and would lead to a revival of the glacial period. Bonney thinks that during 

 the glacial period the temperature of England was about 20° F. lower than it now is, and 

 the mean temperature of the earth's atmosphere as a whole was from 15° to 20° F. lower 

 than at present. Bruckner states that a lowering of the earth's temperature to the extent 

 of 3° or 4° C. would probably suffice to account for the phenomena of the glacial period. 

 He considers that the change in temperature would be relatively slight in equatorial 

 regions and great in polar regions. Finally, David, from a study of glaciation in Austraha 

 and other less familiar parts of the world, arrives at the conclusion that in order to explain 

 the phenomena of the last great advance of the ice it must be assumed that the temperature 

 of that time was lower than that of the present by "probably not less than 5° C." 



The average value of the decrease in temperature necessary to produce a glacial period, 

 according to the statements of the five authorities cited above, amounts to from 5° to 6° C. 

 That is, they conclude that if the mean temperature of the earth were to fall 5° or 6° C, 

 and were to remain thus low for a sufficient length of time, meteorological conditions would 

 be so altered that a large part of North America would be shrouded with ice down to 

 about the fortieth degree of latitude, and Europe would suffer a corresponding glaciation. 

 If a change of from 5° to 6° C. would produce such a result, it seems reasonable to suppose 

 that the change of 0.26° C. which Newcomb has determined in the eleven-year sun-spot 

 cycle would produce a corresponding result on a smaller scale, provided the duration of 

 the period of low temperature were long enough. To take a specific case for illustration, 

 the Rhone glacier is now barely 6 miles long; the foot of the ice stands at a height of 5,780 

 feet above sea-level and the surface of the ice at its origin is 10,200 feet above the sea. 

 During the period of maximum glaciation the glacier was 240 miles longer than it now is; 

 its foot stood about 4,700 feet lower than is now the case, and its surface near the origin 

 was 1,400 feet above the present surface. 



For the sake of conservatism, let it be assumed that the change of temperature which, 

 together with corresponding changes in winds and precipitation, was necessary to cause 

 the Rhone glacier to assume its former great dimensions was 13° C, which is greater than 

 the maximum figure given above (Bonney's, 20° F., or 11.1° C), and more than twice 

 the mean of the five authorities cited. Then a change of 0.26° C. would be one-fiftieth 

 of the change necessary to cause the Rhone glacier to assume the dimensions which it had 

 during the glacial period. It seems fair to assume that the results of a small change of 

 climate would be approximately proportional to those of a larger change. If this is so, 

 the difference of 0.26° C, which Newcomb finds between the mean temperatm-e of periods 



