Part 8

That direct solar rays are converted into obscure or dark heat rays by contact with the planetary surface, and that the atmosphere of our planet is more transcalent to the former than to the latter, has been fully demonstrated by Tyndall, although slightly modified by Buff.

However small may be the difference between the transcalency of the atmosphere to direct solar rays and to the dark rays into which the direct are converted, a gradual rise in temperature must follow. This rise must follow whether solar energy be constant or slowly decreasing, the rise being due not to the actual amount of heat received, but to the difference between the rate of receipt and the rate of loss.

The great increase of mean surface temperatures in equatorial, temperate and sub-tropical areas being due to this small but positive difference between the rates of receipt and loss; as has just been shown, this action is yet in progress.

These deductions are radically at variance with the opinion of high authorities on meteorology, as may be seen from the following quotation: “It is evident that our planet, considered as a whole, and on the average of many years, loses all the heat that it receives from the sun, but all the details of this process have not yet been worked out.”

The author is unable to find any facts to sustain this view--all tend to refute it. The trapping of heat by vapors and gases of the atmosphere--the gradual retreat of glaciers in both hemispheres--and the vast rise in temperatures since the culmination of the Ice Age--all conclusively tend to corroborate the deductions just reached--namely, that the mean surface temperatures of the globe have been and are yet rising from the trapping of heat.

It does not follow that this rise has an indefinite or excessive limit, as the oceans become warmer they are cooled by giving off more vapor. This vapor, when partly condensed into clouds, intercepts solar heat in the upper atmosphere, and the intense white of the upper surface of clouds reflects more heat into space than the darker planetary surface beneath.

The vast store of cold in the continental ice sheets has been greatly exhausted; there yet remains the vaster store in the ice cold depths of the oceans, the conservative influence of which cannot be estimated; for besides the difficulties of heating water from the surface downwards, there yet remains the cooling effect of surface evaporation. There is thus presented the extreme slowness of the methods by which vast changes are wrought. Here are agencies whose results are so slight as not to be detected by thermometric methods--yet recording their effects in grand eras of climates throughout the earth.

The planet Mars is particularly interesting, having a mass less than one-ninth (1/9.4) that of the earth. His loss of internal heat occurred ages before that of the earth; therefore, Mars has been a heat-gathering body longer than the earth, and enjoys a milder general temperature, although that planet receives less than half the heat and light received by the earth. Jupiter is in a condition which our geological history proves the earth to have passed through; Mars is in a condition towards which the earth is gradually tending.

It is now a simple matter to trace the steps by which glacial conditions were removed and zones of climate established.

Solar energy first established its control in that zone most exposed to its power--namely, the torrid zone. From this zone glacial conditions were first removed, and this removal continued north and south upon lines parallel with present isotherms.

In considering the astronomical causes, and the physical results thereby brought about, it was argued that these causes tended to heat the northern hemisphere more rapidly than the southern. Dr. Croll and other physicists, have so fully discussed this question that there remains but little to be added.

The prime reason, however, seems to have been omitted, which is simply this, the northern hemisphere, containing so large a predominance of land area, was more easily warmed than the southern. This unequal heating once inaugurated would establish currents both of air and water tending to perpetuate this action, reinforced as it is by geographical and cosmical agencies.

When, by this gradual accession of heat, conditions and temperatures resembling those existing prior to the Ice Age, were re-established, we find these new conditions restricted to latitudinal belts sensibly parallel with the equator, but modified by elevation and ocean currents; whereas the corresponding pre-glacial climates were independent of latitude.

By the trapping of solar heat a gradual rise in temperature was inaugurated at that period, when by the exhaustion of the earth heat, left in the oceans, the enshrouding clouds were removed. Then, and not until then, do we find the removal of conditions shutting out solar heat written in zones of life belting the earth. In these new zones of climate there have been developed higher, nobler types of life, and with the birth of the seasons there was ushered in upon the earth that Light which is developing Psychozoic Life.

FOOTNOTES

In 1821 Venetz called attention to the once greater extension of Glaciers; and in 1824 Prof. Esmark made similar observations as to the Glaciers of Norway. Phil. Mag., Vol. XXVII, p. 321.

As early as 1821 a prize of 300 livres was offered by the Helvitic Soc. of Nat. Sci. for the collection of facts regarding the increase or decrease of the extension of glaciers in the Alps. Tillock’s Phil. Mag., Vol. LVII, p. 307.

But to Agassiz belongs the honor of having first pointed out the existence of the Ice Age when all glaciers were vastly more extended than at present.

The writer prefers the nomenclature of Dr. Geikie and others using the term Ice Age rather than Glacial Epoch, or Period. The duration of this age was not recorded in the same manner and terms as either previous or succeeding ages; this is due to the inactivity, or even absolute suspension of the great forces, heat and moisture, over continental areas during this age; under estimates of its duration are thus liable to be made.

This question is so important and has so broad a bearing that it will be reverted to later under the heading Palæozoic Glaciation.

Transactions of the Technical Society of the Pacific Coast, Sept., 1891, Vol. VIII. See also The Climate Controversy, S. V. Wood, Jr., Geol. Mag., 1876 and 1883. Climate and Time, Climate and Cosmology, Croll. Island Life, Alfred Russell Wallace, F. R. S., etc. Philosophical Magazine, May, 1864. British Association Reports, part 2, p. 11. Proceedings Royal Soc., vol. xxviii, p. 15. Quart. Jour. Geological Soc., Feb., 1878. Nature, July 4, 1878. Trans. Geological Soc., Glasgow, Feb. 22, 1877. The Ice Age in North America, Dr. Fred. G. Wright, Appendix by Warren Upham. The Cause of an Ice Age, Sir Robert Ball, F. R. S., etc. Révolutions de la Mer. Déluges Périodiques, Alphonse Joseph Adhémar.

See also The Date of the Last Glacial Epoch. Gen. Drayson, R. A. Science, Nov. 25, 1892.

Elements of Geology, Le Conte, 2d Edition, page 578.

Stellar heat having the same function as solar heat, and being sensibly a constant of unknown amount but much less than solar heat, need not be separately considered in further discussion of the question.

The proposition here stated is applicable to any planet. It is probable that Mars, Venus and Mercury have passed through periods corresponding to our Ice Age; and that Jupiter, Saturn, Uranus and Neptune have not reached theirs. A study of Jupiter in this connection is particularly instructive. Phenomena are presented which are easily explained by the theory under discussion. See Zenographical Fragments, London, 1891. Also the author’s views in Circulation of the Atmosphere of Planets. Trans. Technical Society of the Pacific Coast, Vol. XI, No. 4, pp. 127-143.

There were circumstances protecting certain areas, such as the “Unglaciated Area,” in the basin of the Yellowstone River, in North America. Here vast and continuous lava overflows in Wyoming, Idaho, Oregon and Washington, liberated earth heat; which heat, borne easterly by the general circulation of the atmosphere, caused the precipitation upon the “Unglaciated Area” to be warm rains instead of snow. To this region the animals of the tertiary period retreated as glacial conditions surrounded them. Here they were protected, and perpetuated their species, and in these regions vast quantities of their remains are found. Mining and Scientific Press, Feb. 14, 1892.

The easterly projection of the unglaciated area is opposite the corresponding projection in the lava overflow. How this simple explanation has escaped the researches of geologists is not known.

Maury, Physical Geography of the Sea, 6th Edition, p. 212, et seq. Croll, Climate and Time, p. 60, et seq. Also, Climate and Cosmology, p. 51.