CLIMATE AND THE CLIMATIC ZONES (1) How Climate Acts as a Barrier on the Ocean.—Climate limits - man's movements directly when a rainstorm keeps people in the house for example, or a gale prevents ships from going to sea. Its chief effects, however, are indirect or in combination with other factors. For example, a large part of the difficulty in crossing oceans and mountains is climatic. America did not remain undiscovered so long merely because of the broad ocean, but because people feared that climatic conditions in the form of storms and winds would wreck them or prevent them from coming home again. To-day travelers do not fear the ocean when it is calm, but only when it is disturbed by cli matic influences such as winds, waves, fogs, and icebergs like that against which a great ship called the Titanic struck her bows and sank with 1500 people. The effectiveness of the ocean as a barrier would be greatly reduced if the climatic dangers could be eliminated.
How Climate Sets up a Barrier among Mountains.—In the same way the barrier of the mountains is largely climatic. For instance, in crossing the Himalayas from India to western China the steep slopes and thin air are indeed a great hindrance. Yet these direct effects of relief are far less dreaded than are the climatic conditions of low temperature, nipping wind, and fierce snowstorms, followed by the blinding glare of the sun. Worse still are the climatic conditions that cause avalanches which sometimes bury whole caravans, and glaciers where man and beast sometimes plunge to their death in deep cre vasses. Worst of all is the absence of vegetation, because the climate is so cold that on vast stretches of high barren plateau no one can dwell and not even grass can grow. It is so difficult to bring food there that among the caravans on the way from India to western China, hundreds of weakened animals die each year from hunger and exposure. In a single day's journey a traveler counted 32 dead horses that had recently fallen by the trail; the next day he counted 220; and the third day 474, in addition to one human corpse. All that was due to the cold climate acting either directly through storm and wind, or indirectly through the absence of vegetation.
How Climate Bars the Way within the Frigid Zone.--The climate
of cold regions erects barriers even more impassable than those of mountains and oceans. The world's largest unexplored areas are the snowy plateaus of Antarctica and Greenland and the bitterly cold regions of northern America and Asia. So impassable are the great fields of snow and ice that the poles were not reached till the present century in spite of attempt after attempt. Peary reached the North Pole and Amundsen the South only after long experience had taught explorers how best to use dogs and other means of trans portation, how to carry and store great supplies of food and fuel, and how to provide the warmest clothing and shelter.
How Climate Acts as a Barrier in Deserts.—Next in difficulty to the climatic barrier of cold regions come hot, dry deserts. In southern Arabia the desert climate makes such a barrier that no explorer has ever penetrated a region hundreds of thousands of square miles in ex tent. The natives fear this region not only because there is no water, but because of the extreme difficulty of climbing the lofty dunes of dry, sliding sand piled up hundreds of feet by violent winds. When the wind dies down the dust settles in the low flat areas between the dunes. As no rain falls for years at a time the dust becomes so deep that one sinks in it above the ankles even on the edges, and every movement raises it in stifling, choking clouds. No one dares go farther for fear of sinking deeper and then falling and being smothered.
How Climate Sets up a Barrier in Tropical Forests.—The damp heat of tropical forests creates a barrier to human movement almost as serious as that of deserts. Not only does such heat cause the growth of dense forests through which travel is almost impossible, but it is most exhausting to human energy, and fosters some of the world's most deadly fevers. Even so wise and vigorous an explorer as Theodore Roosevelt was baffled by the barrier of the South American forests, and could not escape the ravages of tropical fever. Thus on oceans, among mountains, in deserts, and in both high and low latitudes such climatic conditions as high winds, intense cold, extreme aridity, and damp tropical heat, are among the circumstances most unfavorable to man's movement from place to place.