Climate
the characteristic condition of a country with reference to heat, moisture, wind, and healthfulness. If a region be studied, it will be found that while the winters may differ greatly from year to year, average conditions are much the same. One day may be clear, another cloudy; yet the rainfall in the Mohawk Valley for any series of ten years is much the same. One day may be hot, the next cool; yet the average temperature of New Orleans from year to year varies little. The same is true of winds. One day may be windy, the next calm; yet a region subject to south winds will have much the same amount of south wind from year to year. The rainy winds of India do not blow from the south for a series of years, then turn around and blow from the north for a few years. Weather is very changeable; climate varies little.
Latitude is the chief factor that affects climate. Our heat is derived from the sun. The nearer the equator, the more vertical are the sun's rays. Within the tropics a bundle of rays spreads over less than half the surface that it covers within the polar circles. The poles are about 4,000 miles farther from the sun than is the equator; but the sun is so far from the earth that this slight difference in distance has no practical effect. The coldness of the Arctic regions is due to the fact that an acre of ground receives only half as much heat as an acre in the torrid zone.
Altitude, or height above the sea level, is another important factor. The earth's atmosphere, that is to say, the air, allows the heat of the sun to pass through it freely to the earth's surface, but acts like a blanket, preventing the escape of the radiated heat; that is to say, heat coming from the sun comes through the air readily, but is so changed by radiation on turning back from the earth that it cannot escape through the air readily. The higher one ascends above the sea level the less dense the air. High plateaus and mountain ranges are colder than corresponding regions at the sea level, not because they receive less heat from the sun, but because they have a thinner air blanket with which to retain the heat. An increase of 300 feet in altitude is considered equivalent to an increase of one degree in temperature. Scientists allow a change of one degree in temperature for each 300 feet of ascent. The summits of the mountains in the Andes lying directly on the equator are covered with snow the year around, and have much the same climate as is found at the sea level in northern Greenland.
Moisture is an important factor in climate. The Pacific and Atlantic coasts of South America, particularly in the latitude of the La Plata, have a very different climate owing to a difference, chiefly, in rainfall. The prevailing winds in this belt are from the east. The coast of southern Brazil has abundant rainfall, which extends inward for a long distance. The winds are robbed of their moisture, however, by the Andes, so that the Pacific coast of northern Chile lying in sight of the ocean is practically a rainless desert, almost devoid of vegetation. Some regions have so much rain that they are swampy and unhealthful.
Two types of climate--the continental and the oceanic--require special mention. Water heats more slowly and cools more slowly than land. Large bodies of water, therefore, prevent excessive heat in summer and excessive cold in winter. The British Isles, surrounded entirely by the ocean, have a cool summer and a warm winter. They possess an oceanic climate. The upper Mississippi Valley, on the contrary, remote from the ocean, warms up in the summer and cools off in winter. It possesses a continental climate.
Generally speaking, a region having a medium temperature with a moderate amount of rainfall, well distributed through the year, is considered to have the most desirable climate. Local pride usually comes to the defense of local climate. Most would agree, however, that central and western Europe, and portions of North America, have the most desirable climate in the world.