544 E. HUNTINGTON SOLAB HYPOTHESIS OF CLIMATIC CHANGES 



POSSIBLE EXPLAXATIOXS OF HISTORIC CHANGES OF CLIMATE 



The meteorological hypothesis. — ^Let us now see how far each of the 

 main hypotheses of climatic change is competent to explain these historic 

 changes. Omitting the precessional hypothesis as no longer a possibility, 

 we have six others before ns. They are the meteorological, volcanic, de- 

 formational, and carbonic acid hypotheses, and the solar hypothesis in 

 its old or ^^caloric" form and in its new or ^^cyclonic" form. The historic 

 fluctuations, as sho\^TL in the California curve, for example, seem to be 

 of such length and magnitude that they can scarcely be due to purely 

 meteorological causes. The meteorological hypothesis is so vague, how- 

 ever, relying as it does on mere accidents, that it presents no tangible 

 points of contact by which it can be proved or disproved. It stands, 

 therefore, as a last resort so long as no other hypothesis offers a better 

 explanation. 



The volcanic hypothesis. — The next hypothesis is that of volcanic dust. 

 We must assume, apparent^, that just as the meteorological hypothesis 

 is of great importance when we. come to the details of the weather of 

 every day, so the volcanic hypothesis is of importance at particular times. 

 So far as the past 3,000 years are concerned, however, there seems to be 

 no good reason for assuming that its importance has been any gi'eater 

 than during the last 30 years. The recorded volcanic eruptions show no 

 apparent relation to the climatic changes indicated in the California 

 curve. If there had been volcanic eruptions sufficient to cause the pro- 

 nounced pulsation which figure 14 shows to have occurred between 1300 

 and 1500 A. D., it seems scarcely credible that they should have attracted 

 so little attention. TTe can not assert this positively, however, for certain 

 parts of the world where volcanoes are now important were not then 

 known and their history is not recorded even by tradition. Our chief 

 reason for believing that the volcanic hypothesis is of only minor impor- 

 tance is that this appears to be its position today, and that the same seems 

 to be true of the geological past, a? Professor Schuchert points out in 

 "The Climatic Factor.'' 



The solar hypothesis — General discnssiou. — The hypotheses of crustal 

 deformation and of carbonic acid gas were never intended as explana- 

 tions of fluctuations which from the geological point of view are so small 

 and short as those now before us. They are of the greatest importance 

 when Glacial periods are considered, but for the present they do not con- 

 cern us. The solar hypothesis, therefore, remains as the only one to be 

 considered. Inasmuch as we have already seen reason to choose the cy- 

 clonic form in preference to the caloric, we shall confine our attention 

 to the former. Two questions present themselves: In the first place, 



