The Establishment of Solar Climates.
At the culmination of the Ice Age the snow line was much lower than at present, and elevated lands[28] at all latitudes were deeply glaciated; the seas were intensely cold. It is evident that since the culmination of the Ice Age and in the establishment of the present climates there has been a great rise in temperatures in the tropical, temperate and sub-frigid zones. There is also indisputable evidence that this rise in temperature is yet in progress. This accession of heat must therefore be accounted for by the correct application of laws and forces now acting, and it is not necessary to go outside of these known laws and forces to render a correct interpretation of the establishment and maintenance of the zones of climate now existing.
It will be observed that when the oceans were exhausted of their heat and the lands deeply glaciated, the crust was shrunk in upon the interior mass by being uniformly chilled down to the lowest temperature to which a planet, upon which water and an atmosphere exist, can be subjected. The atmosphere was then cleared of clouds and heat rays from exterior sources permitted to reach the planetary surface. At once these rays began to be changed into dark heat rays, particularly those from water, and the trapping of heat ensued; from this date a general rise in temperatures must follow from the accession of heat from exterior sources, until checked within the moderate limits hereafter outlined.
The trapping process thus inaugurated is independent of the actual amount of heat received whether from solar or stellar sources.
Were it possible for the now pent-up internal heat to raise the temperature of the oceans, the crust at the bottom of the oceans, and under the polar ice caps to a mean temperature of say 68 degrees Far., the accession of heat from exterior sources would be shut off, as in early Quaternary times, by dense clouds; the exterior would be again shrunk by glacial conditions, the air cleared as before and heat from exterior sources in whatever amounts it then reached the surface would be trapped as succeeded the Ice Age.
This action must in turn take place upon any planet upon which water and an atmosphere resembling ours exist. The rate at which a planet acquires heat from exterior sources is dependent upon the power of its atmosphere to trap heat; very slight variations in the atmospheric constituents producing great variations in heat trapping power.
The trapping process not being a function of the orbital distance, nor of the actual amount of heat received, but of the composition of the atmosphere, this rise, being only a function of the amount received and not of the trapping process, this rise in temperature is as certain to follow in one position as another.
By thus being subjected to the maximum shrinking-strains the weakest portions of the crust were ruptured. The lava ejected from these ruptures was spread out over the weak areas in successive layers of a few dozen feet in thickness until the added strength reached that belonging to thousands of feet of solid rock.[29]
To digress a moment—
These lava overflows evidently performed another important function. The heat set free by each successive layer could not have been lost by radiation into space, for the enshrouding clouds had not yet been removed. The air and clouds caught this heat and bearing it eastwardly in their general course caused warm rains instead of snow to be precipitated upon the adjacent region. In this way the “unglaciated area” escaped glaciation; in this area are the “bad lands” of Dakota, whose topography distinctly shows that sub-aerial denudation, and not glacial ice formed the controlling features. In this area are the great deposits of tertiary fossil life, in perfect form—uncrushed by the mighty tread of the glaciers which surrounded them on all sides, except to the west. From areas such as these went forth the life that survived the glacial winter.
That the isotherm marked by glacial ice is yet slowly retreating upward is recorded not only by tradition and history but geologically and physically, as observed by every scientist who has studied existing glaciers.[30]
This retreat is a positive proof of either a decrease in precipitation on the tributary areas, a rise in temperature, or both of these agencies acting conjointly. There is no evidence to show that a decrease in precipitation[31] is synchronously taking place over the sub-frigid, temperate and tropical regions of both hemispheres, as is the retreat of glaciers; and there are positive and active causes in force which have affected, and are yet affecting an increase in temperature. We must therefore conclude that this rise in the isotherm marking glacial ice is due primarily, if not entirely, to an accession of heat.
It has been demonstrated that at the culmination of the Ice Age, much colder conditions existed than at present. It now remains to explain the conditions acting to bring about existing climates. Upon the exhaustion of the last available remnant of earth heat—left in the oceans by reason of the high specific heat of water—the supply of vapor maintaining the cloud envelope was shut off, and solar heat permitted to reach the planetary surface.
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,[32] although slightly modified by Buff.[33]
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.[34]”
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.[35]
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,[36] 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.[37]
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.