86 



ANALYSIS OF THE ENVIRONMENT 



dents, are usually more or less favorable. 

 On the other side, Russell (1941, p. 92) 

 wrote: "Though firm advocates of climatic 

 cycles will sharply disagree, such facts as 

 we possess today neither definitely demon- 

 strate nor disprove the existence of any 

 real cycle. Such climatic variability as has 

 been observed may be explained as result- 

 ing from random fluctuations." 



rhe sunspot cycle of shghtly more than 

 eleven years has attracted much attention 

 from ecologists and others. The underlying 

 causation ot this cycle is still unknown. The 

 cycle itself consists of the periodic varia- 

 tion in numbers of sunspots and is charac- 

 terized, in part, by the tendency to remain 

 at one length of period during a number 

 of repetitions and then to shift to some 

 other value that is again repeated for a 

 time. Since 1750 the periods have varied 

 from approximately eight to sixteen years. 

 Even average values vary between 11.13 

 and 11.6 years, and a period of 10.2 years is 

 seriously advanced for the sunspot series 

 between 1615 and 1788 A.D. (Douglass, 

 1936). The variation reflects the continuing 

 inexactness of the basic data regarding 

 weather and chmate (as well as population 

 density), combined at times with the ac- 

 ceptance of indications as a substitute for 

 rigorous proof. 



Solar radiation appears to be less when 

 there are few (or many) sunspots; a maxi- 

 mum of radiation is reached when the sun- 

 spot number is about 100. It appears that 

 the temperature at the earth's surface tends 

 to be highest when the actual solar radia- 

 tion is least during this particular cycle of 

 radiation. The reasons for this paradox are 

 not yet wholly clear. Shifts on the order 

 of 1 or 2 per cent in intensity of radiation 

 are matters of record. If other conditions 

 remained constant, as they would not do, 

 an increase of 1 per cent in solar radiation 

 would produce a rise of about 0.75° C. in 

 the mean temperature at the earth's sur- 

 face, since this temperature varies essen- 

 tially as the fourth root of the intensity of 

 the radiant energy received from the sun. 

 The reasoning that other conditions would 

 not remain stationary while the inten- 

 sity of solar heat varies is based, in part, 

 on the knowledge that resulting variations 

 in tempera. Mre bring about important 

 changes in atmospheric pressure, and the 

 final effect is to decrease temperature in 

 areas cold for their latitude, while those 



wann for their latitude have increased 

 warmth (Brooks, 1926). 



It has been estimated that temperature on 

 the earth might vary about 0.6° C during a 

 sunspot cycle. Small as this amount is, it 

 represents an appreciable fraction of the 

 lowering of temperature that would bring 

 about an ice age. A more recent test of the 

 correspondence between sunspot cycles was 

 made by using temperature records from six 

 scattered tropical stations, covering a period 

 of fifty-eight years. Tropical stations were 

 chosen, since many writers have stated that 

 the closest correlation between sunspots and 

 weather is to be found in the tropics. When 

 the available records were combined in 

 cycles equal to the sunspot cycle of eleven 

 years, a mean temperature ampHtude of 

 0.22° C. was found. The correlation be- 

 tween sunspot number and the annual tem- 

 perature was found to be —0.37, a correla- 

 tion which, although low, probably indi- 

 cates statistical vaHdity (Elton, 1924; 

 Adams and Nicholson, 1933). 



Brooks (1926, p. 409) summed up the 

 situation about sunspot cycles as follows: 

 "The most perfect example of a solar rela- 

 tionship hitherto found in purely meteor- 

 ological data is shown by the level of equa- 

 torial Lake Victoria. Generally speaking the 

 eleven-year cycle is characteristic of equa- 

 torial regions while the thirty-five year 

 Briickner cycle is characteristic of higher 

 latitudes. The amplitude and regularity of 

 the eleven-year cycle decreases toward the 

 poles, those of the Briickner cycle increase 

 from the equator toward the North Pole at 

 least." 



The most discussed biotic cycles include 

 (1) the lemming and mouse cycle of three 

 to four years; (2) the varying hare and 

 lynx cycle of somewhat less than ten years; 

 (3) a cycle corresponding to the sunspot 

 cycle of somewhat more than eleven years 

 which we have been discussing; and (4) 

 another cycle corresponding to the Briick- 

 ner cycle of about thirty-five years. 



As critical studies accumulate, it becomes 

 difficult to discover biological phenomena 

 exactly coinciding with the last two cycles, 

 even as it is difficult to find a sound envi- 

 ronmental periodicity that corresponds with 

 the first two cycles just listed. Goldie's 

 (1936) suggestion of maxima as related 

 to the mean cycle of annual air drift over 

 the northern part of the British Isles that 

 recurs at an interval of somewhat less than 



