DISCOVERY 



79 



article, \\hat has been said will be sufficient to give 

 the reader an insight into the methods which are used 

 to give the values of the vipper winds to be found in 

 the reports and forecasts in the daily Press. 



Sunspots and Climate 



Recent discoveries in climatology-, in astronomical 

 physics, in geologj', and in archasologj' have been col- 

 lected together in an amazingly interesting book ^ and 

 utilised to give an explanation of the cause of climatic 

 changes both in geological and in historical time. The 

 book contains infornaation of many kinds, carefully sifted 

 and admirably set forth, in addition to the authors' 

 fertile theories and their deductions therefrom. It 

 illustrates very well the resource, the insight, and the 

 ingenuity of the human mind in face of a difficult problem. 



Climatic change in the past has been always an interest- 

 ing subject. Less than thirty thousand years ago most of 

 our country was under a sheet of ice. At another time 

 its climate was even more genial than that at present. 

 To-day most of Greenland is under ice ; it is hard to 

 believe that once coral reefs fringed its shores and palm 

 trees grew on its lands. At one time indeed the climate 

 of the earth seems to have been so equable that many 

 plants and animals could Uve 1,500 and at other times 

 even 4,000 miles farther from the Equator than now. 

 Changes in wetness have also been great. There are 

 to-day deserts in Asia, even now a feat to cross, which 

 were once so fertile as to support tribes and even contain 

 cities. Nor are these changes confined to the remote 

 past. In the fourteenth centiury a.d., for instance, it 

 was possible once or twice to cross the Baltic from Germany 

 to Sweden on the ice. 



The explanation of these changes and others, less 

 striking but no less interesting, is a very difficult matter. 

 Some, of course, present less difficulty than others. Day- 

 to-day \-ariations of weather are easily explained, and 

 nobody needs to be told more than once why summer 

 is warmer on the average than winter. But why are 

 certain areas every eleven or twelve years subjected to 

 abnormally disturbed weather ? WTiy is something of a 

 similar kind said to occur every thirty-three years ? 

 What is at the bottom of the so-called liistorical pulsa- 

 tions ? For example, the twelfth or tliirteenth centurj- 

 before Christ was verv dry, so were the seventh and the 

 thirteenth of our era if the thickness of the annual rings 

 of the large trees in California and Arizona affords a 

 rehable indication of the amount of moisture available 

 during the period of gro\v-th. The fourteenth century' 

 A.D., on the other hand, was a time of great climatic 

 severity in many parts of both the Old and the New Worlds 

 which ordinarily ha\e mild climates. 



• Climatic Changes. Their Nature and Causes. By Ells- 

 worth Huntington and Stephen Sargent Visher. (London : 

 Humphrey Jlilford ; New Haven : Yale L'niversity Press, 

 175. 6d.) 



iluch more difficult to give is an explanation of the' 

 Ice Age. About 30,000 years ago the Ice Age was at its 

 lieight in our own country, in parts of North America, 

 but not in corresponding parts of Asia. Why do ice ages 

 occur, and why do they occur, as they appear to do, at 

 irregular intervals ? All these and cognate problems are 

 very carefuly stated by the authors of this book before 

 they attempt to solve them. And they have a solution. 

 But before gi'ving it they describe and criticise the 

 hypotheses of climatic change that have been put forward 

 in the past. Each of these, they think, is of importance, 

 but none is really the fundamental one. Variations in 

 the position of the earth when it is nearest the sun, thev 

 believe, have a real though slight influence in causing 

 cycles with a length of about 2r,ooo years. Changes in 

 the amount of the gas carbon dioxide in the air probably 

 have a more important but extremely slow influence on 

 the climate over large periods of time. Variations in the 

 size, shape, and height of the continents are constantly 

 causing all manner of climatic complications. These, 

 however, do not cause rapid fluctuations nor pulsations. 

 The eruption of volcanic dust (which acts as a screen to 

 the sun's rays) appears occasionally to lower the tem- 

 perature, but it is probable that this cause is less important 

 than many geologists have believed. There is finally 

 the possibility that variation in the position of the poles 

 might be a factor in climatic changes. This theory has 

 been adduced in two main forms. First, the " pendula- 

 tion " theory, which supposes that the earth's poles 

 swing very slowly backwards and forwards about an axis 

 joining a point in Ecuador with one in Sumatra. Varjdng 

 distances from the pole, of course, cause changes of 

 climate, " and the mo\'ements of the ocean, which adjusts 

 itseK to the change of pole more rapidly than the land, 

 causes the great transgressions and regressions of the 

 sea and the elevation and subsidence of the land." 

 Secondly, there is the theory of Wegener,- which explains 

 the apparent variation in the position of the pole by the 

 assumption that the earth's crust is moving slowly over 

 the earth's core so that the axis, wthout necessarily 

 changing its position, passes through different parts of 

 the crust at different epoclis. 



A simpler and, they believe, a better explanation than 

 any of these is the authors' sunspot hypothesis. This 

 briefly put is as follows : The climate of the earth is 

 regulated by the sun, and consequently varies in harmony- 

 with any disturbance in the amount of radiant energy 

 the latter sends out. The times of these disturbances 

 are known because they occur when spots on the sun are 

 \-isible — a sunspot being a part of the sun's disk where 

 more than the normal amount of energj' is poured out. 

 The consequence on the earth of spots on the sun is not, 

 however, as might be imagined, a general rise in tempera- 

 ture. It is more complex than that. For the earth's 

 temperature is conditioned not only by the energy it gets 

 from the sun, but also by the energy it radiates into space. 

 And it is possible, and does, as a fact, happen, that the 



- For further information on this theory readers are referred 

 to Professor Wegener's article on The Origin of Continents 

 and Oceans, Discovery, vol. iii. No. 29. 



