DO \'OLCAXIC EXPLOSIONS AFFECT OUR CLIMATE? 



197 



The volcanic effect, if here present, is 

 certainly obscured by other intluences. 



As stated above, there seems to be a 

 strong indication that the mountain sta- 

 tions were rendered appreciably cooler 

 by the explosion 'of June, 1912. In order 

 to see if a similar effect was caused by 

 the dust cloud emanating from Krakatoa 

 in 1883, I have studied the temperature 

 departures for Pic du Midi, Puy de 

 Dome, and Schneekoppe for the years 

 1882 to 1884, inclusive, but there does 

 not appear to have been at that time any 

 such decrease of temperature following 

 the eruption of Krakatoa, August 27, 

 1883, as occurred in July, 1912. Never- 

 theless at Pic du Midi there was a very 

 well marked decrease in the daily tem- 

 perature range, beginning with Septeni- 

 Der. 1883. I have found for some other 

 stations a similar decrease of the daily 

 temperature range following the erup- 

 tion of Krakatoa. 



The fact is that the temperature of the 

 earth is a function of so many variable 

 quantities that general or cosmical ef- 

 fects are often greatly obscured by local 

 ones. Studies have, however, been made 

 by various authors to detect if there is a 

 periodicity of terrestrial temperature cor- 

 responding in time to the sun-spot cycle 

 of about 1 1 years, and it has been found 

 by Koppen, Arctowski. Nordmann, New- 

 comb, Abbo^ and Fowle, and others that 

 there is indeed an increased temperature 

 at the time of minimum sun-spots. This 

 increase of temperature is greater than 

 would be caused directly by the darken- 

 ing of the sun by sun-spots, so that it is 

 supposed that there is accompanying the 

 spots some secondary influence affecting 

 terrestrial temperatures. 



The fluctuations of temperature are, 

 however, not fully accounted for by the 

 march of the sun-spots, and I have en- 

 deavored to see whether a combination 

 of the well-known eft'ect of the sun-spot 

 cycle with the effect of the volcanic haze 

 will produce a more exact correspond- 

 ence between the cosmical phenomena 

 and the temperature of the earth. 



Referring to page 196, the curve (A) 

 is a smoothed representation of the aver- 

 age intensity of the direct solar radiation. 

 The method of smoothing the curve is as 



follows, taking for example the year 

 1895 • -^^^^ to the value for 1894 twice 

 that for 1905 and that for 1896 and 

 divide by 4. Curve (B) is the smoothed 

 sun-spot curve as given by Wolfer. The 

 sun-spot numbers run from o to about 80 

 Curve (C) is a combination of (A) and 

 (B). They are taken in the following 

 proportions: Multiply the percentage de- 

 parture of radiation by 6* and subtract 

 from it the sun-spot number for the given 

 year. Curve (D) represents the depart- 

 ures of mean maximum temperature for 

 15 stations of the L'nited States distrib- 

 uted all over the country. It is smoothed 

 in the same manner as curve (A). Curve 

 (E) represents the departures of tem- 

 perature for the whole world, also 

 smoothed in the same manner as curves 



(A) and (D). The data for the curves 

 (D) and (E) are taken from Annah, 

 Astrophysical Observatory, volume 2, 

 page 192, and from the Monthly Weather 

 Review of the United States Weather 

 Bureau. 



Although there is a considerable de- 

 gree of correspondence between curve 



(B) and curve (D), yet it is not hard 

 to see that there is also much of discord- 

 ance. 



For example, the sun-spot maximum 

 of 1893 was greater than that of 1883 

 or 1906, yet the temperature curve (D) 

 indicates a gradual increase of tem- 

 perature for the three periods ; also the 

 temperature had begun to fall in 1890, 

 although sun-spots were still at the mini- 

 mum, and the temperature had begun to 

 rise in 1892. although sun-spots had not 

 yet reached their maximum. 



Similar discrepancies occur in other 

 parts of the curves, but when we com- 

 pare the curves (C) and (D), that is to 

 say, the combination of. the effects of 

 sun-spots and volcanic haze, with the 

 mean maximum temperature for the 

 L^nited States, the correspondence of the 

 curves is most striking. 



CONCLUSION 



It seems to me, in consideration of 

 this, that there can be little question that 

 the volcanic haze has very appreciably 



* T incline now to think a better result would 

 have come if 5 were used instead of 6. 



