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.
It follows that if the Rocky Mountains were lowered as described, the entire United States would be green with rich vegetation and there would be no deserts anywhere within its broad boundaries. Also, if the Appalachian Range were as high as the Rocky Mountains—as it may have been at one time—and if it extended around the Gulf of Mexico as well as up through our Atlantic Coast States, the vaporous atmosphere of the Atlantic Ocean and of the Gulf of Mexico would be prevented from entering the interior of the continent, and the power that to-day stands as the greatest bulwark of civilization would not exist. There would be but a narrow fringe of vegetation upon its east and its west coasts; the interior, with its vast cotton and cereal plains, would be a barren waste.
But to revert for a moment to Jefferson. He took his thermometer to Philadelphia when he proceeded there on a mission that would have caused any less serene and courageous spirit to forget all the small details of life. When the debates upon which hung the fate of a nation and, in fact, the lives of those that participated, were in progress, he coolly hung his thermometer on the wall and noted down its readings. Those historians who have described the intense heat in Independence Hall on the Fourth of July, 1776, were mistaken, as will be shown by reference to his observations, the early and the late ones of which doubtless were made at his lodgings. They are as follows: 6 A.M., 68°; 9 A.M., 72¼°; 1 P.M., 76°; and 9 P.M., 73½°.
Jefferson had one of the only two barometers in this country at that time. James Madison (the Bishop, not the President) had the other. They took readings at the same hour of the day for a considerable period of time, and Jefferson discovered that changes in the pressure of the air always began on his instrument a few hours before they did on his friend’s instrument a couple of hundred miles to the east of him. He came near discovering the fact that no matter what the direction of the wind, storms almost universally move from the west toward the east. When the British captured Washington they also raided Monticello, Jefferson’s home in Virginia, and they destroyed his barometer. It has been said that he was as much distressed over the loss of his special instrument of science as he was over the burning of the National Capitol.
In “Descriptive Meteorology” (Appleton), the writer expressed doubt that there had been important changes in climate within the period of authentic history, but recent researches cause him to change his opinion, for the evidence now seems almost conclusive that marked changes have occurred. The powerful kingdoms of Sumeria, Babylonia, Assyria, and Persia, each ruling many centuries and dominating all or a large part of the vast region from the Persian Gulf to the Caspian Sea and westward to the Mediterranean and Egypt, covering in their various reigns some four thousand years before Christ, could hardly have built their many great cities, supported their numerous millions of population, and developed the trade and commerce that was theirs with the climatic conditions as they exist to-day. As late as the opening of the Christian Era, Palmyra, in Syria, had a population of from one hundred and fifty thousand to two hundred thousand people, was opulent and adorned with a comparatively high civilization. To-day we see the wreckage of its vast aqueduct and irrigating systems, which are unable to gather enough water to wet their well-constructed walls, and a few hundred people eke out a miserable existence where once was a metropolis teeming with life under luxurious conditions. The same picture is shown in more or less relief throughout the greater part of the region that once maintained the greatest empires of antiquity. But we must not assume that such dry and nearly barren conditions are to continue forever; rather are we to imagine that within a cycle of a few thousand years this region may have a rebirth of abundant vegetation and again throb with the pulsations of abounding life.
The record inscribed by the waters on the abandoned and the submerged shores of inland lakes and seas in the Rocky Mountains, and on the shores of the Caspian Sea and other waters, is easy to read. It shows several great oscillations of climate in the United States and the most civilized portions of the world since the birth of Christ. For some time before and for several centuries after the beginning of our era there was a wet period. The Caspian Sea stood some one hundred feet higher than now and an abandoned beach and a clearly marked shore line show that Lake Owens, in California, on the east side of the Sierras, existed at a level nearly two hundred feet higher than now. There was an abundance of water to irrigate the Holy Land, and although the center of dominating human power had long since passed in succession Babylon, Assyria, Persia, Greece, Macedon, and was working its way towards the Atlantic, the Mesopotamian Valley was abundantly fruitful.
Then, for six or seven hundred years, with short-period variations of from thirty to fifty years, the world inhabited by civilized man and large areas in the temperate zone not yet civilized, grew drier. The Caspian Sea fell to a lower level than it now maintains, for the ends of great walls, constructed to keep out barbarians, and other evidences of the handiwork of man, are now many feet below the surface of the water. This is the driest time known to history. Ellsworth Huntington of Yale, acting under the auspices of the Carnegie Foundation at Washington, made an examination of many of the stumps of the big trees of California, ranging in age from one to four thousand years. The thickness of each ring of annual growth is a legible record of the wetness or the dryness of the year. One would hardly think of these towering giants of the floral kingdom as being both thermometers and rain gauges, accurately measuring and recording the dry-hot and the wet-cold periods for thousands of years, and now at the end of their majestic careers revealing the hidden secrets of past ages. Huntington and Cushing, in “Principles of Human Geography”, say:
“The rings dating from the time of Christ are thick and indicate that at that time, when Palmyra had an abundant supply of water, when Owens Lake overflowed and there was high water in the Caspian Sea, the big trees also had plenty of water and grew rapidly. Six or seven hundred years later, when Palmyra was abandoned and when the Caspian Sea stood fifteen or twenty feet lower than at present, the trees formed only narrow rings, because the climate was dry. The way in which the growth of the trees has varied is shown in Figure 30. The high part of the curve indicates abundant rainfall. The black shading at the bottom indicates periods of comparative aridity.”
Since the extensive system of observations by the Weather Bureau was inaugurated, some fifty years ago, it has been revealed to us that frequently the Ohio Valley would suffer a deficit in rainfall that would persist for periods as great as five or six years, while New England and the South Atlantic States, or other large areas of the country, had an excess. This is an illustration that excesses in one part of the country were balanced by shortages in other parts that occurred at the same time. But the long-period oscillations in climate that are measured in hundreds of years instead of tens—these changes seemed to have occurred simultaneously in the middle latitudes of Europe and America. These changes were simultaneous in an east and west direction. Now we have evidence of such long-period changes in a north and south direction which were simultaneous, but of an opposite character, indicating that during the Christian Era the eastward track of storms has oscillated northward and southward. This would account for the occurrence of dry and of wet periods simultaneously throughout the vast stretch of territory between southern California and the Caspian Sea. In Guatemala, Yucatan, and other Central American countries there are ruins of cities and the evidence of an agriculture and a civilization that could not have been established with the torrential rains and jungle growths that now prevail in those regions. During the centuries when the big trees of California were receiving a large rainfall and making a thick annual growth, especially about the beginning of the Christian Era, because of a northward shifting of the climatic zone, the precipitation in Yucatan and Guatemala had so diminished as to leave only the amount of rainfall that could be economically employed in agriculture and in the rearing of great cities; and then, with a southward migration of the rain belt, these cities were suffocated with excessive precipitation, agriculture rendered impossible, and their temples and palaces buried beneath the gloom of a tropical growth.
If we are to reason from the records of the past it seems highly probable that at least the middle latitudes of the Northern Hemisphere are slowly passing out of a dry period that has prevailed for the past two hundred years or more. For several hundred years all the great glaciers have receded, but we should not expect such recession to continue indefinitely. Geology furnishes abundant evidence that great changes took place in the climate of the earth during the prehistoric ages; that there were several glacial periods, the last occurring during pleistocene times, somewhere between twenty and fifty thousand years ago, and that there were intervals between the culminations of the Ice Ages of probably fifty thousand to one hundred thousand years. Between these long winters, that have meant death and desolation to much of what are now the most civilized portions of the earth, there have been warm periods of thousands of years’ duration.
Fossil remains show that regions far north, now covered with perpetual ice, once supported a luxuriant flora and fauna, and many regions in the temperate and equatorial zones that are now deserts were once overgrown with forests and teeming with animal life. The fundamental thing of the cosmos is change—birth, growth, maturity; then decline, senility, death, decay, disintegration; and always a renaissance, or new birth. Energy and life seem to be eternal, but ever undergoing change. The Great Ice Cap may again cover New England, the region of the Great Lakes, and flow southward to the Ohio River, but the change will be so gradual, if it does come, that there will be no great cities to be ground beneath the feet of the boreal monster; cold that will precede the ice cap will destroy them and they will be buried beneath the dust of accumulating ages before their icy tombstone is erected. Then the healthful and invigorating climate of the north part of our country will be transferred to the region of the Gulf of Mexico. Civilization will and must migrate with the shifting of the climatic belts. Because these changes cannot possibly concern us personally, we have almost neglected the study of the great forces that silently yet most persistently are at work altering the conditions under which future man must live and work out the destiny of coming generations.
Effects of Forests on Climate and Floods. Next to the fallacious belief in a change of climate during the life of an individual there are few if any errors that have gained such wide acceptance as a belief that the cutting away of the forests has caused a marked change in climate and especially in the frequency and intensity of floods and droughts. The writer shared in the mistake with regard to the influence of the forests in restraining run-off and augmenting floods, until compelled by an order of the Congress of the United States to prepare a report on the floods of the nation that had occurred during the time of the gradual reduction of the forest areas. Dividing into two equal periods the forty years for which the Weather Bureau has comprehensive records of the rainfall upon the catchment basins of the Tennessee, the Cumberland, and the Ohio rivers, and for which it has records of the height of the rivers, contrary to his belief, he found that the high waters were no higher with a given rainfall, the floods of no longer duration, nor the low waters of summer lower, during the last half of the period than during the first half.
It is now pretty generally conceded by hydraulic engineers that the broken, permeable soil of the husbandman, frequently stirred by cultivation a part of the year and filled with countless billions of the tiny water-absorbing rootlets of the grasses and the cereal crops during the remainder of the annual period, is equally as good a conserver of the rainfall as the forests themselves, even if it is not better.
Some years ago the writer was delivering a series of Chautauqua lectures. He arrived at Devil’s Lake, North Dakota, and found that the Chautauqua amphitheater was on the banks of Devil’s Lake, once bordering the town, but now receded to a distance of five miles and confined to a narrow valley. In driving from the city to the lecture hall he remarked to his escort that they seemed to be traveling along the bottom of an ancient lake. His companion said, “Yes, a lake, but not an ancient one. Fifty years ago I used to dive off a springboard right there in front of the railroad station.” In the course of his lecture the writer referred to this incident and told them that, contrary to their belief, their climate had not changed, that fifty years ago they sold their old lake to some gentlemen in Chicago and that they had been selling it over again every year since; that the former compact surface of the virgin prairie resisted the penetration of the rainfall, or at least only slowly absorbed it, and allowed it to collect in the depression adjacent to the city; but now, in the broken, permeable soil of the farmer it was taken up by millions of tiny rootlets and the hand of the Great Alchemist had transformed their lake into wheat, the sale of which was responsible for the presence of the speaker on the platform of a largely-attended Chautauqua. The lake had gone never to return unless the region were again to become the haunt of the buffalo and the prairie dog instead of civilized man. The rainfall was the same, but it was now being utilized for the benefit of mankind.
In this problem of rainfall, floods, and the forests, most persons assume that when the forest is cut the land is at once denuded of vegetation. On the other hand a second growth will effectually shade the soil within a few months or a few weeks after the large trees are removed, and if the land is cleared and rendered fit for the plow, growing crops take the place of the forest-covering the greater portion of the time.
There is an abundance of reasons for the protection of our diminishing forests and for the creation of new forest areas without assigning to the forests functions that they do not exercise. The covering of an area by a great city, a village, a forest, a barn, or a tent modifies the climate of the particular area covered so long as the covering remains, but there is no appreciable climatic effect a few feet above the surface of the earth between a forest and a field of grain. The climate of a region like the American continent is controlled fundamentally by the great oceans that wash its shores, by the trend of its mountain systems and their height, and by the direction of its prevailing winds. The vast vaporous atmosphere that flows inland from the Atlantic Ocean to the foothills of the Rocky Mountains, deluging our cereal plains with its life-giving precipitation will continue its pluvial generosity without any heed whatever to the puny scratchings of man upon the surface of Mother Earth. Nothing that man can do will intensify drought conditions on this continent or augment the volume of floods. It is time that we return to sanity in considering this matter instead of being frightened by the dire forebodings of well-meaning but purely visionary enthusiasts, no matter how noble their aspirations may be or how self-sacrificingly they have consecrated themselves to the redemption of humanity.
It is certain that forests restrict the flow of moderate falls of rain, but they do not restrain the flow of flood waters, because, surprising as it may seem to one who has not tested the matter, floods do not occur until after all surfaces, open fields and forests alike, have become saturated, and then the run-off of the two surfaces is equal.