Influences of Geographic Environment, Ellen Churchill Semple [classic novels for teens .txt] 📗
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Climatic conditions limit the habitable area of the earth. This is their most important anthropo-geographic effect. At either pole lurks an invincible foe, with whom expanding humanity must always reckon, and who brooks little encroachment upon his territory. His weapon is the restriction of organic life, without which man cannot exist. The geographical boundaries of organic life, however, are wider than those of human life. The consequence of this climatic control, therefore, is not only a narrowed distribution of the human race, but a concentration which intensifies the struggle for existence, forces the utilization of all the available area, and thereby in every locality stimulates adaptation to environment.
Man ranks among the most adaptable organic beings on the earth. No climate is absolutely intolerable to him. Only the absence of food supply or of all marketable commodities will exclude him from the most inhospitable region. His dwellings are found from sea level up to an altitude of 5000 meters or more, where the air pressure is little over one half that on the coast.1412 Seventeen per cent. of the towns and cities of Bolivia are located at an elevation above 13,000 feet (4000 meters), while Aullagas occupies a site 15,700 feet or nearly 5000 meters above the sea.1413 Mineral wealth explains these high Bolivian settlements, just as it draws the Mexican sulphur miners to temporary residence in the crater of Popocatepetl at an altitude of 17,787 feet (5420 meters), from their permanent dwellings a thousand meters below.1414 The laborers employed in the construction of the Oroya railroad in Peru became rapidly accustomed to work in the rarefied air at an elevation of 4000 to 4800 meters. The trade routes over the Andes and Himalayan ranges often cross passes at similar altitudes; the Karakorum road mounts to 18,548 feet (5,650 meters). Yet these great elevations do not prevent men going their way and doing the day's work, although the unacclimated tenderfoot is liable to attacks of mountain sickness in consequence of the rarefied air.1415
Man makes himself at home in any zone. The cold pole of the earth, so far as recorded temperatures show, is the town of Verkhoyansk in northeastern Siberia, whose mean January temperature is 54 F. below zero (-48 Centigrade). Massawa, one of the hottest spots in the furnace of Africa is the capital of the Italian colony of Eritrea. However, extremes both of heat and cold reduce the density of population, the scale and efficiency of economic enterprises. The greatest events of universal history and especially the greatest historical developments belong to the North Temperate Zone. The decisive voyages of discovery emanated thence, though the needs of trade and the steady winds of low latitudes combined to carry them to the Tropics. The coldest lands of the earth are either uninhabited, like Spitzenbergen, or sparsely populated, like northern Siberia. The hottest regions, also, are far from being so densely populated as many temperate countries.1416 [See maps pages 8, 9, and 612.] The fact that they are for the most part dependencies or former colonial possessions of European powers indicates their retarded economic and political development. The contrast between the Mongol Tunguse, who lead the life of hunters and herders in Arctic Siberia, and the related Manchus, who conquered and rule the temperate lands of China, shows how climates help differentiate various branches of the same ethnic stock; and this contrast only parallels that between the Eskimo and Aztec offshoots of the American Indians, the Norwegian and Italian divisions of the white race.
Mean Annual Isotherms And Heat Belts [Centigrade 0°C = 32°F. 20°C = 68°F. 30°C = 86°F.]
Mean Annual Isotherms And Heat Belts
[Centigrade 0°C = 32°F. 20°C = 68°F. 30°C = 86°F.]
The zonal location of a country indicates roughly the degree of heat which it receives from the sun. It would do this accurately if variations of relief, prevailing winds and proximity of the oceans did not enter as disturbing factors. Since water heats and cools more slowly than the land, the ocean is a great reservoir of warmth in winter and of cold in summer, and exercises therefore an equalizing effect upon the temperature of the adjacent continents, far as these effects can be carried by the wind. The ocean is also the great source of moisture, and this, too, it distributes over the land through the agency of the wind. Where warm ocean currents, like the Gulf Stream and Kuro Siwa, penetrate into temperate or sub-polar latitudes, or where cool ones, like the Peruvian and Benguela Currents wash the coasts of tropical regions, they enhance the power of the ocean and wind to mitigate the extremes of temperature on land. The warm currents, moreover, loading the air above them with vapor, provide a store of rain to the nearest wind-swept land. Hence both the rainfall and temperature of a given country depend largely upon its neighboring water and air currents, and its accessibility to the rain-bearing winds. If it occupies a marked central position in temperate latitudes, like eastern Russia or the Great Plains of our semi-arid West, it receives limited moisture and suffers the extreme temperatures of a typical continental climate. The same result follows if it holds a distinctly peripheral location, and yet lies in the rain-shadow of a mountain barrier, like western Peru, Patagonia and Sweden north of the sixtieth parallel. [See map page 484.]
Owing to the prevalence of westerly winds in the Temperate Zones and particularly in the North Temperate Zone, the mean annual temperature is high on the western face of the northern continents, but drops rapidly toward the east.1417 This is especially true of winter temperatures, which even near the eastern coast show the severity of a continental climate. Sitka and New York, Trondhjem and Peking have the same mean January temperatures, though Peking lies in about the latitude of Madrid, over twenty-three degrees farther south.
Europe's location in the path of the North Atlantic westerlies, swept by winds from a small and narrow ocean which has been super-heated by the powerful Gulf Stream, secures for that continent a more equable climate and milder winters than corresponding latitudes on the western coasts of North America, whose winds from the wide Pacific are not so warm.1418 Moreover, a coastal rampart of mountains from Alaska to Mexico restricts the beneficial influences of the Pacific climate to a narrow seaboard, excludes them from the vast interior, which by reason of cold or aridity or both must forever renounce great economic or historical significance, unless its mineral resources developed unsuspected importance. In Europe, the absence of mountain barriers across the course of these westerly winds from Norway to central Spain, and the unobstructed avenue offered to them by the Mediterranean Sea during fall and winter, enable all the Atlantic's mitigating influences of warmth and moisture to penetrate inland, and temper the climate of Europe as far east as St. Petersburg and Constantinople. Thus several factors have combined to give the western half of Europe an extraordinarily favorable climate. They have therefore greatly broadened its zone of historical intensity toward the north, pushed it up to the sixtieth parallel, while the corresponding zone in eastern Asia finds its northern limit at the fortieth degree.
Moisture and warmth are essential to all that life upon which human existence depends. Hence temperature and rainfall are together the most important natural assets of a country, because of their influence upon its productivity. The grazing capacity and wheat yield of southern Australia increase almost regularly with every added inch of rainfall.1419 The map of population for the Empire of India clearly shows that a high degree of density accompanies a high and certain rainfall. Exceptions occur only where hilly or mountainous tracts offer scant arable areas, or where plains and valleys are sparsely populated owing to political troubles or unhealthiness. Nearly three-tenths of the population are found crowded together on the one-tenth of India's level territory which is blessed with a rainfall above the average for the country.1420 Deserts which yield nothing are purely climatic phenomena. Steppes which facilitate the historical movement, and forests which block it, are products of scant or ample precipitation. The zonal distribution of rainfall, with its maxima in the Tropics and the Temperate Zones, and its minima in the trade-wind belts and polar regions, reinforces and emphasizes the influence of temperature in determining certain great cultural and economic zones.
In equatorial regions, which have an abundant rainfall throughout the year, agriculture is directed toward fruits and roots; only in certain districts can it include cereals, and then only rice and maize. The temperate grains demand some dry summer weeks for their maturity. Excessive moisture in Ireland has practically excluded wheat-growing, which in England and Scotland also is restricted chiefly to the drier eastern counties.1421 It thrives, on the other hand, in Manitoba and the Red River region even with a short season of scant rainfall, because this comes in the spring when moisture is most needed.1422 Most important to man, therefore, is the question how and when the rainfall is distributed, and with what regularity it comes. Monsoon and trade-wind districts labor under the disadvantage of a wet and dry season, and a variability which brings tragic results, since it easily reduces a barely adequate rainfall to disastrous drought. These are the lands where wind and weather lord it over man. If the rains hold off too long, or stop too soon, or withhold even a small portion of their accustomed gift, famine stalks abroad.
Temperature, the other important element of climate, depends primarily upon zonal location, which has far different historical results from central and peripheral location, continental and insular. It determines the amount of heat received from the sun, though air and ocean currents may redistribute that heat within certain limits, and humidity or aridity modify its effects. Still zonal distinctions remain. The great climatic regions of the earth, like the hot, wet equatorial belt or the warm, dry trade-wind belts
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