PREDICT 10 X OF CLIMATIC VARIATIONS 



99 



work long hours each day. Thus they 

 too have more money than usuah and 

 begin to buy freely. That stimulates 

 business still more. Meanwhile the 

 railroads are busy l)eeause the crops 

 supply abundant freight, and the goods 

 consumetl by the farmers give the roads 

 something to carry back. On all sides 

 business booms and the country prospers. 

 There may of course be over production, 

 or troubles of other kinds, but these 

 rarely bring grave and prolonged dis- 

 aster unless the crops are poor. When 

 the crops fail every sort of activity 

 declines. The farmers are the founda- 

 tion of prosperity; their prosperity de- 

 pends on the weather; hence the weather 

 is the greatest of all factors in determin- 

 ing whether business in general shall 

 prosper and pay good dividends. By 

 saving the farmer, we shall also save 

 the whole country. 



If the value of long range weather 

 forecasts is so great, why have we made 

 so little progress in finding out how to 

 make them? Can we ever, indeed, hope 

 to make much progress? To answer 

 these cjuestions we must inquire into the 

 state of our knowledge of the causes of 

 climatic variability. 



The old hypothesis, and the one that 

 is today most generally accepted, is that 

 "the wind bloweth where it listeth, and 

 thou hearest the sound thereof, but 

 canst not tell whence it cometh and 

 whither it goeth." In other words, 

 the differences which we continually 

 observe between a wet season this year 

 and a dry season next year are thought 

 to be due to chance. An accidental 

 combination of circumstances may cause 

 a swing, now in this direction and now 

 in that. If this were the case, long range 

 predictions would be out of the question. 

 We might possibly progress so far as to 

 predict in weeks where we now predict 

 in days, but there would be no reason- 



able hope of l)eing able to predict 

 months or years ahead. Thoughtful 

 meteorologists however, have rarely 

 been fully satisfied with this hypothesis. 

 They have been convinced that the 

 ol)ser\ed changes are too extensive to 

 be so nearly accidental. Hence there 

 has been a constant searcli for underly- 

 ing principles. 



One result of this search has been to 

 bring to light some interesting minor 

 causes of climatic instability. For ex- 

 ample, Pettersson, the director of the 

 Swedish Hydrographical-Biological Sur- 

 vey has discovered that the strength of 

 the tides, which varies regularly in a 

 cycle of about eighteen years, has an 

 influence upon the amount of water that 

 comes into the Baltic Sea from the ocean. 

 This in turn has an influence upon the 

 surface temperature of the Baltic, and 

 thus upon the degree to which the winds 

 blowing from it are warmed or cooled. 

 Again, Humphreys, Abbott and Fowle 

 have shown that the presence of vol- 

 canic dust in the air after explosive 

 eruptions, such as that of Krakatao in 

 1883, shuts out a certain amount of 

 sunlight and slightly lowers the mean 

 temperature of the earth's surface. The 

 eft'ect is slight however, and cannot be 

 the main cause of climatic variations. 



Since the sun is the source of heat, 

 there has always been speculation as to 

 how much this heat may vary and what 

 effect may thus be produced upon the 

 earth's climate. As the sun's activity 

 varies in the sunspot cycle of about 

 eleven years, there has been a strong 

 tendency among persons untrained in 

 meteorology to suppose that changes in 

 the sunspots may be the direct cause of 

 exceptional seasons. Reasonable as this 

 supposition appears upon its face, it has 

 not found much support among pro- 

 fessional students of climate until within 

 a few vears. The reason is that there 



