CYCLES 133 



CYCLES AND CLIMATE 



Three major lines of interest have emerged in this study of cycles 

 as it has developed in this chapter. The first was the distribution of 

 cycles over western areas in approximate simple fractions of 35 years 

 (or perhaps the triple sunspot value of 33.94 years) ; the second is the 

 history of cycles in the long Flagstaff record and their agreement with 

 solar changes, thus throwing light on solar history; the third now to be 

 considered is the problem of prediction, which depends directly on the 

 climatic significance of the cycles previously discussed. Their climatic 

 character seems open to no reasonable doubt. Dating and prediction, 

 the backward look and the forward look, both depend on a knowledge 

 of the historic and geographical distribution of these cycles. In each 

 it is better to test out a small locality first, such as the Flagstaff region, 

 in order to avoid the complexities which arise over too large areas. 



First caution: Interpretation differs with locality — The Arizona 

 trees respond closely to a definite weather element, rainfall, the most 

 important element in the prosperity of the country, but in the moist 

 areas this direct response decreases and even disappears. Hence, the 

 first caution in this process is that we must not assume relationships 

 similar to those in Arizona in any given place until that place has been 

 thoroughly investigated. 



Second caution: Cycle changes not understood — The second 

 caution is very important. Until we know the physical cause of cycles 

 we can not say how long a mechanical repetition will last, for it may 

 break down at any time. This is well illustrated in the solar changes 

 shown in the long Flagstaff record. For hundreds of years the 11 -year 

 cycle was dominant, and then in the middle of the seventeenth century 

 it faded out and gave place to others, and we do not yet know the 

 reason. Until we know the reason we can not be sure it will not happen 

 again in the near future. Fortunately, we have the long-lived sequoia 

 for testing out secular changes. The best results from it at the present 

 time were given in a historical summary above. 



Variable star analogy — There are several variable stars which are 

 dominated by different periods for irregular intervals of time. One of 

 the best is SS Cygni, which has been observed carefully for more than 

 30 years. It is not visible to the naked eye, but by telescopic observa- 

 tion has been found to rise suddenly from the twelfth to the eighth 

 magnitude at intervals of 50 or 60 days, more or less. Alternate 

 maxima are often of different length, reminding us of alternate sun- 

 spot maxima. Then without warning the period changes. Dr. Leon 

 Campbell, of Harvard College Observatory, has given me data and 

 for years I have tried to find the rule which governs these changes. 



Third caution: Cycle subdivisions — The splitting of cycles that 

 may differ in different localities causes an uncertainty in place of 



