480 E. HUNTINGTON SOLAR HYPOTHESIS OF CLIMATIC CHANGES 



may be the rule in all parts of the world. This opinion is, of course, 

 open to question ; but even those who oppose the idea of any permanent 

 change during historic times are willing to accept the idea of cycles 

 with a duration of centuries.^ So careful and conservative a clinuitolo- 

 gist as Hann, the author of a work on Climatology which is universally 

 accepted as a standard, is convinced that, in central Asia at least, the 

 climate has changed during the past two thousand years.* In the second 

 place, various lines of evidence, part of which have been presented else- 

 where^ and part of which will be presented here, seem to show that pres- 

 ent variations of climate are connected with solar changes much more 

 closely than has hitherto been supposed. Moreover, these changes, in 

 spite of their short period, show a considerable number of phenomena 

 which display a striking similarity to the vastly greater phenomena of 

 Glacial periods. 



In view of these facts, it is not impossible that the cause of glaciation, 

 or at least an important contributory cause, may be discovered by a study 

 of present climatic variations. Accordingly, the first portion of this 

 paper will be devoted to an investigation of the causes of present climatic 

 variations — a line of study which leads at once to a consideration of the 

 possible relationship between terrestrial climate and the activity of the 

 sun's surface. The object before us is primarily geological, but in treat- 

 ing this part of our subject we shall be obliged to follow meteorological 

 methods. By so doing we shall be prepared to take up the purely geo- 

 logical phases of the matter, for the facts here presented suggest strongly 

 that the present is the key to the past. 



That the climate of the earth varies from year to year needs no demon- 

 stration. The variations can readily be seen in equatorial and polar 

 regions ; they become more pronounced in the sul)tropical zone, and thoy 

 I'each their highest development in the temperate zone of cyclonic storms. 

 The first step in obtaining a satisfactory knowledge of climatic varia- 

 tions of all kinds, whether large or small, would seem to be to ascertain 

 the cause of such differences between the weather of one year and an- 

 other. Three hypotheses seem to be worthy of consideration. The firsl 

 is the common meteorological explanation. The second is the new hy- 

 pothesis of volcanic dust. The third is the solar hypothesis, which lias 

 hitherto been somewhat indefinite. Ijot us consider each of thorn in deiail. 



3 For Instance, in the Geographical Journal for 1014 .T. W. Gregory and P. Kropatkiii 

 advocate the hypothesis of climatic uniformity and of progressive desiccation, respec 

 tlvely, but both admit cycles having a duration of centuries. In the Annales de Geo- 

 graphie for 1014 Ilerbetle makes a siniilar admission, although he strongly opposes the 

 present author's general conclusions as to pulsatory climatic changes. 



♦ T. Hann : Klimatologie. Stuttgart, lOO.S. vol. 1. p. 352. note. 



» Ellsworth HuDtlnpton ; The Climatic Factor. Washington, 1914. 



