Part 3 (1/2)
[Footnote 10: James Croll: Climate and Time, 1876.]
[Footnote 11: T. C. Chamberlin: An attempt to frame a working hypothesis of the cause of glacial periods on an atmospheric basis; Jour. Geol., Vol. VII, 1899, pp. 545-584, 667-685, 757-787.
T. C. Chamberlin and R. D. Salisbury: Geology, Vol. II, 1906, pp.
93-106, 655-677, and Vol. III, pp. 432-446.
S. Arrhenius (Kosmische Physik, Vol. II, 1903, p. 503) carried out some investigations on carbon dioxide which have had a p.r.o.nounced effect on later conclusions.
F. Frech adopted Arrhenius' idea and developed it in a paper ent.i.tled Ueber die Klima-Aenderungen der Geologischen Vergangenheit. Compte Rendu, Tenth (Mexico) Congr. Geol. Intern., 1907 (=1908), pp. 299-325.
The exact origin of the carbon dioxide theory has been stated so variously that it seems worth while to give the exact facts. Prompted by the suggestion, of Tyndall that glaciation might be due to depletion of atmospheric carbon dioxide, Chamberlin worked up the essentials of his early views before he saw any publication from Arrhenius, to whom the idea has often been attributed. In 1895 or earlier Chamberlin began to give the carbon dioxide hypothesis to his students and to discuss it before local scientific bodies. In 1897 he prepared a paper on ”A Group of Hypotheses Bearing on Climatic Changes,” Jour. Geol., Vol. V (1897), to be read at the meeting of the British a.s.sociation at Toronto, basing his conclusions on Tyndall's determination of the competency of carbon dioxide as an absorber of heat radiated from the earth. He had essentially completed this when a paper by Arrhenius, ”On the influence of carbonic acid in the air upon the temperature of the ground,” Phil.
Mag., 1896, pp. 237-276, first came to his attention. Chamberlin then changed his conservative, tentative statement of the functions of carbon dioxide to a more sweeping one based on Arrhenius' very definite quant.i.tative deductions from Langley's experiments. Both Langley and Arrhenius were then in the ascendancy of their reputations and seemingly higher authorities could scarcely have been chosen, nor a finer combination than experiment and physico-mathematical development.
Arrhenius' deductions were later proved to have been overstrained, while Langley's interpretation and even his observations were challenged.
Chamberlin's latest views are more like his earlier and more conservative statement.]
[Footnote 12: C. G. Abbot and F. E. Fowle: Volcanoes and Climate; Smiths. Misc. Coll., Vol. 60, 1913, 24 pp.
W. J. Humphreys: Volcanic dust and other factors in the production of climatic and their possible relation to ice ages; Bull. Mount Weather Observatory, Vol. 6, Part 1, 1913, 26 pp. Also, Physics of the Air, 1920.]
[Footnote 13: H. Arctowski: The Pleonian Cycle of Climatic Fluctuations; Am. Jour. Sci., Vol. 42, 1916, pp. 27-33. See also Annals of the New York Academy of Sciences, Vol. 24, 1914.]
[Footnote 14: W. Koppen: uber mehrjahrige Perioden der Witterung ins besondere uzer die II-jahrige Periode der Temperatur. Also, Lufttemperaturen Sonnenflecke und Vulcanausbruche; Meteorologische Zeitschrift, Vol. 7, 1914, pp. 305-328.]
CHAPTER IV
THE SOLAR CYCLONIC HYPOTHESIS
The progress of science is made up of a vast succession of hypotheses.
The majority die in early infancy. A few live and are for a time widely accepted. Then some new hypothesis either destroys them completely or shows that, while they contain elements of truth, they are not the whole truth. In the previous chapter we have discussed a group of hypotheses of this kind, and have tried to point out fairly their degree of truth so far as it can yet be determined. In this chapter we shall outline still another hypothesis, the relation of which to present climatic conditions has been fully developed in _Earth and Sun_; while its relation to the past will be explained in the present volume. This hypothesis is not supposed to supersede the others, for so far as they are true they cannot be superseded. It merely seems to explain some of the many conditions which the other hypotheses apparently fail to explain. To suppose that it will suffer a fate more glorious than its predecessors would be presumptuous. The best that can be hoped is that after it has been pruned, enriched, and modified, it may take its place among the steps which finally lead to the goal of truth.
In this chapter the new hypothesis will be sketched in broad outline in order that in the rest of this book the reader may appreciate the bearing of all that is said. Details of proof and methods of work will be omitted, since they are given in _Earth and Sun_. For the sake of brevity and clearness the main conclusions will be stated without the qualifications and exceptions which are fully explained in that volume.
Here it will be necessary to pa.s.s quickly over points which depart radically from accepted ideas, and which therefore must arouse serious question in the minds of thoughtful readers. That, however, is a necessary consequence of the attempt which this book makes to put the problem of climate in such form that the argument can be followed by thoughtful students in any branch of knowledge and not merely by specialists. Therefore, the specialist can merely be asked to withhold judgment until he has read all the evidence as given in _Earth and Sun_, and then to condemn only those parts that are wrong and not the whole argument.
Without further explanation let us turn to our main problem. In the realm of climatology the most important discovery of the last generation is that variations in the weather depend on variations in the activity of the sun's atmosphere. The work of the great astronomer, Newcomb, and that of the great climatologist, Koppen, have shown beyond question that the temperature of the earth's surface varies in harmony with variations in the number and area of sunspots.[15] The work of Abbot has shown that the amount of heat radiated from the sun also varies, and that in general the variations correspond with those of the sunspots, although there are exceptions, especially when the spots are fewest. Here, however, there at once arises a puzzling paradox. The earth certainly owes its warmth to the sun. Yet when the sun emits the most energy, that is, when sunspots are most numerous, the earth's surface is coolest.
Doubtless the earth receives more heat than usual at such times, and the upper air may be warmer than usual. Here we refer only to the air at the earth's surface.
Another large group of investigators have shown that atmospheric pressure also varies in harmony with the number of sunspots. Some parts of the earth's surface have one kind of variation at times of many sunspots and other parts the reverse. These differences are systematic and depend largely on whether the region in question happens to have high atmospheric pressure or low. The net result is that when sunspots are numerous the earth's storminess increases, and the atmosphere is thrown into commotion. This interferes with the stable planetary winds, such as the trades of low lat.i.tudes and the prevailing westerlies of higher lat.i.tudes. Instead of these regular winds and the fair weather which they bring, there is a tendency toward frequent tropical hurricanes in the lower lat.i.tudes and toward more frequent and severe storms of the ordinary type in the lat.i.tudes where the world's most progressive nations now live. With the change in storminess there naturally goes a change in rainfall. Not all parts of the world, however, have increased storminess and more abundant rainfall when sunspots are numerous. Some parts change in the opposite way. Thus when the sun's atmosphere is particularly disturbed, the contrasts between different parts of the earth's surface are increased. For example, the northern United States and southern Canada become more stormy and rainy, as appears in Fig. 2, and the same is true of the Southwest and along the south Atlantic coast. In a crescent-shaped central area, however, extending from Wyoming through Missouri to Nova Scotia, the number of storms and the amount of rainfall decrease.
[Ill.u.s.tration: _Fig. 2. Storminess at sunspot maxima vs. minima._ (_After Kullmer._)
Based on nine years' nearest sunspot minima and nine years' nearest sunspot maxima in the three sunspot cycles from 1888 to 1918. Heavy shading indicates excess of storminess when sunspots are numerous.
Figures indicate average yearly number of storms by which years of maximum sunspots exceed those of minimum sunspots.]
The two controlling factors of any climate are the temperature and the atmospheric pressure, for they determine the winds, the storms, and thus the rainfall. A study of the temperature seems to show that the peculiar paradox of a hot sun and a cool earth is due largely to the increased storminess during times of many sunspots. The earth's surface is heated by the rays of the sun, but most of the rays do not in themselves heat the air as they pa.s.s through it. The air gets its heat largely from the heat absorbed by the water vapor which is intimately mingled with its lower portions, or from the long heat waves sent out by the earth after it has been warmed by the sun. The faster the air moves along the earth's surface the less it becomes heated, and the more heat it takes away. This sounds like a contradiction, but not to anyone who has tried to heat a stove in the open air. If the air is still, the stove rapidly becomes warm and so does the air around it. If the wind is blowing, the cool air delays the heating of the stove and prevents the surface from ever becoming as hot as it would otherwise. That seems to be what happens on a large scale when sunspots are numerous. The sun actually sends to the earth more energy than usual, but the air moves with such unusual rapidity that it actually cools the earth's surface a trifle by carrying the extra heat to high levels where it is lost into s.p.a.ce.