The new air world

by Willis L. Moore

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.