The writer would again caution the reader not to be misled by any pseudoscientist, no matter how worthy his purpose may be, who would teach that the operations of men in changing forest areas to cultivated fields, gardens, villages, and cities, has in the slightest degree harmfully affected the climate, or augmented floods or intensified droughts. A field of grass, of wheat, of corn; an orchard of fruit; a highway bordered with towering, majestic oaks and elms; or a grove of cultivated trees about a prosperous home is just as beneficial to the climate as the thickest and most impenetrable forest and far more pleasing to the eye and helpful to mankind. Forests should be protected, conserved, and grown because we need timber, not because a lot of foolish people are writing nonsense about them.
Influence of Lakes and Rivers. With the exception of contributing to the formation of occasional fogs over their surfaces and the adjacent low lands, through the rising of warm water vapor into the cold air that often collects at the bottom of valleys during nighttime, rivers exercise little influence on climate. Lakes exert a modifying influence on the temperature of places near their shores but only for a few miles therefrom, and they are too small to exert any appreciable influence on rainfall. If one examine charts showing the average rainfall for the United States by seasons, he will observe that the amount gradually shades off as the distance from the Gulf or Ocean increases, without any relation whatever to the five Great Lakes. Deserts exist on either side of the Caspian Sea, although it slightly increases the rain of the Elburz Mountains to the south. If these great bodies of water do not influence the rainfall, how ridiculous to assume that the changing of forest areas to other forms of vegetation possibly can affect precipitation or influence droughts. Stress is laid on the fact that some land is left bare and then is eroded into deep gullies. This is true, but the fault is one that may be corrected by a proper system of plowing and cultivation. And at most the area so eroded is so infinitesimal in comparison to the vast regions changed from forests to growing crops as to be negligible.
Chart 14.—Mean Annual Isotherms (Buchan).
Influence of Ocean Currents on Climate. Climates are markedly influenced by the currents of oceans. [Charts 15] and [16] show the normal wind circulations of the globe; note that the centers of the great swirls are coincident with the location of the High and the Low centers of action located on [Charts 1] and [2]. Next observe [Chart 13], showing the ocean currents, and it will be seen at once how closely the circulation of the great ocean currents follows that of the winds, due to the friction of the air upon the water, and to the interposition of bodies of land that turn about or deflect the currents.
Chart 15.—Normal Wind Direction and Velocity for January and February (Köppen).
Chart 16.—Normal Wind Direction and Velocity for July and August (Köppen).
Water has a greater capacity for heat than nearly any other substance. It requires ten times the quantity of heat to raise a pound of water one degree that it does a pound of iron. The oceans therefore store up vast quantities of the heat of the sun and, unlike the continents, distribute this heat northward and southward without regard to latitude. Much of the heat of the tropics is thus transported far northward and southward from the equator. The extensive eddy-like circulation of the south half of the North Atlantic Ocean sends currents northward along the coast of the United States which set eastward at latitude 40°. A part of these reach the coast of Spain and then turn south; the greater part spread out in mid-ocean and move northeast, bathing the coasts of the British Islands, Iceland, and Norway. They still retain some of the heat that they absorbed from a tropical sun, and they therefore give to the coasts that they reach a higher temperature than they would have if the ocean waters were moving from the north, or than they would have if there were no currents at all. On [Chart 14] note how the isothermal lines are carried northward by these currents as they cross the Atlantic Ocean. The Gulf Stream mingles with these northeast currents but adds little to their temperatures, for the general ocean circulation would produce practically the same effects if there were no Gulf Stream.