Enough has been said to indicate that climate is nearly as important to animal life as it is to the vegetable existence, and that a cold climate, if it be not so extreme as to limit the production of cereal crops, and has frequent changes in temperature, pressure, sunshine, and cloud, favors the development of hardy and resourceful races of men; in fact, that no dominating race can exist without such stimulating conditions of climate.
CHAPTER XIII
HAS OUR CLIMATE CHANGED?
POPULAR OPINION ERRONEOUS, AS THERE IS NO CHANGE WITHIN THE PERIOD OF AN INDIVIDUAL LIFE, BUT MOMENTOUS CHANGES HAVE OCCURRED SINCE THE BEGINNING OF THE CHRISTIAN ERA
One of the hallucinations entertained by nearly every adult person is that the climate has changed since he was young. No matter what the scientists may say, he knows that it has changed. Fifty years ago did he not trudge to school for months every winter in snow knee-deep? Have not the old swimming holes in the brook dried up? Yes, he is a positive witness to an affirmative answer. Even the river of his boyhood, whose broad expanse he conquered in a swimming contest at the tender age of ten—as he views it after an absence of a quarter-century—has dwindled to little more than a creek, across which one easily may hurl a stone. Talk to him about no change in climate. He’s been right on the spot, and knows. For all this, there has been no change during the lifetime of this man; nor has there ever been during the life period of any individual. Mutations, to be sure, are going on all the time, but they are so minute that they do not accumulate a measurable quantity except in periods of hundreds or thousands of years. It is not the climate that has changed; it is the man. The natural action of the stream may have filled the swimming holes; or the stream may have entirely disappeared through much of the contiguous area being brought under cultivation and the water that formerly supplied its flow being utilized in the production of cultivated crops, which actually make use of as much if not more rainfall than the forest that formerly lined its sinuous banks and covered the near-by lowland. And then, snow knee-deep to a boy of ten hardly comes up to the ankles of a man of six feet two. Again, no one can remember the climate of his boyhood; he cannot carry the average in his mind; all that he can remember are a few instances of unusual conditions which because of their unusual character left an impress upon his mind. The river is just as wide as it ever was during the period of his lifetime, or that of his father, or of his grandfather; but he has lived on the broad Mississippi for many years, and when he goes back to the scenes of his youth, his concept of what constitutes a river has undergone a revolutionary change since he left the parental roof to go forth and conquer the world.
An examination of the personal papers of Thomas Jefferson, in the State Department at Washington, by an official of the Weather Bureau, revealed a number of most interesting incidents in connection with the weather observations made by the author of the Declaration of American Independence. He says:
“A change in climate is taking place very sensibly. Both heats and colds are becoming much more moderate within the memory of even the middle-aged. Snows are less frequent and less deep. They do not often lie below the mountains more than one, two, or three days, and very rarely a week. The snows are remembered to have been more frequent, deep, and of long continuance. The elderly inform me that the earth used to be covered with snow about three months in every year.”
But Jefferson and his neighbors were mistaken. Never during the period of authentic history has the snow covered the ground in Virginia an average of three months per year, or three months for a single year. These old inhabitants were like those of to-day, who remember only the abnormalities of climate of twenty-five or fifty years ago, and in comparing the unusual conditions of long ago with the average of the present time they are deceived. I have known intelligent and well-meaning persons to declare that they knew from personal recollection that the climate of their particular places of residence had changed since they were young; that they had stable landmarks to show that the streams were drying up, the rainfall growing less, and the winters becoming milder, notwithstanding the fact that carefully taken observations of temperature and rainfall for each day for over one hundred years right at their places of abode showed no change in climate. We have a continuous daily record for one hundred years at New Bedford, Massachusetts, nearly as long records at several other places, and numerous records for over half a century. From these we learn that there has been no definite change in climate in this country during the past hundred years. There have been variations, such as an excess or a deficiency of rainfall over a considerable area, that have persisted for several years at a time; but in each case the conditions would ultimately come back to normal, or more often to an extreme of the opposite tendency to what had obtained immediately before. In sections where the rainfall in bountiful years is barely sufficient for good crops, the people in the past have been prone to consider that the amount that they receive during the periods of excess is that which normally is due them, and thus to be unprepared for the dry periods that statistics tell us must certainly come. The matter of change of climate is most important to our sub-arid West,—to the western parts of Texas, Oklahoma, Kansas, Nebraska, and the Dakotas. Some years ago, when the tide of emigration was strong into these regions, there were several years of more than the average rainfall. The coming of population and the coming of extra rainfall were accidentally coincident, but that fact was probably responsible for the popular belief that civilization brings an increase in precipitation; that the breaking of the virgin soil, making it more permeable to the absorption of moisture; the planting of trees and the growth of crops, restricting the run-off; the roots of the new vegetable life drawing up the moisture from below the surface of the ground and transpiring it to the air through the leaves of plants; the enormous quantities of water vapor ejected into the air by the combustion necessarily incident to a considerable population,—all had combined to increase the rainfall and render the sub-arid plains more responsive to the efforts of the husbandman. No one can fail to regret that this theory is not founded upon fact. But a moment’s thought by the scientist will indicate to him that the volume of air is so great, and under the heat of the growing period its capacity for moisture so enormous, that the addition of vapor of water by the processes herein described, great though it be, is ineffectual to appreciably change the amount of the rainfall that nature beforehand had ordained should be precipitated.
The size of continental areas, the height and the trend of mountain ranges, the proximity of large bodies of water, and the direction of the prevailing winds are the factors that determine the amount of the precipitation of a region. Against these the puny efforts of man, stupendous though we think them to be, are entirely unavailing. As an illustration: If the Rocky Mountains were as old as the Appalachian Chain, and if they were eroded down to the height of the latter system, the winds from the Pacific Ocean, when they are drawn inland by the cyclonic storms of the Rocky Mountain plateau, or of the Mississippi Valley, instead of depositing their moisture on the west slopes of the first range of mountains, would carry the water vapor of the Pacific clear to that place in the Mississippi Valley where it would meet the moisture drawn by the same storms from the Gulf of Mexico and the Atlantic Ocean. This will appear clear when one understands that cyclonic storms, such as are continually passing across our continent in periods of about three days each, may embrace in their eddy-like circulating systems areas one to three thousand miles in diameter, in which the winds from all directions spirally flow towards the center of the cyclonic system and the system itself is moving eastward.
The water vapor exists as a separate atmosphere from oxygen and nitrogen. It is screened off from the interior of continents by mountain ranges because it is condensed and precipitated as rain or snow at only moderate elevations. The windward side of mountains may, therefore, receive torrential rains while their leeward sides are entirely without precipitation.