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During the early period of the earth’ s history, the weather on earth apparently fluctuated between bright sun and showers. In recent times, however, the mountains and valleys on land and under water have had a great influence on the earth’ s weather. They effect the movements of the thin film of water we call the sea and the thin layer of air around the earth. These movements produce changes in the temperature and humidity prevailing at the surface. Although the sun is approximately 93 million miles away, its rays warm the earth. The areas that receive the sun’ s rays vertically are, naturally, warmer than those areas that receive only slanting raya. 61. Vertical rays do not need to make as long a journey through the atmosphere before reaching the surface of the earth. Therefore, less of their heat is lost in the air and more of their heat is saved to warm the earth. Furthermore, slanting rays are spread over available at a given point. The sun’ s rays do not heat the vast stretches of space between the sun and the earth. 62. If they did, we should expect to be warmer on top of a high mountain or riding in an airplane than we are on the ground. Actually, however, we feel cooler at the top of a mountain; and, if we fly a plane high enough, we encounter freezing temperatures, even over the equator. This is true because the sun’ s rays are like the waves used in radio broadcasting. Music sent out by a radio transmitter does not fill the air with sounds for all to hear. Instead, the music travels in the form of electromagnetic waves, which must pass through a receiver and an amplifier to be heard. 63. Similarly, the sun’ s rays cross our atmosphere and are absorbed by the surface of the earth. These rays warm the surface, which sends back some of this heat into the air. When the air near the earth’ s surface has been warmed, it rises and is replaced by cooler air which comes down to take its place. This cool air, in turn, is warmed and rises to be replaced by more cool air. As air rises it becomes cooler because it expands and is less concentrated, the air is suddenly let out of a tire, the air expands rapidly and becomes much cooler. On the other hand, when air is put under greater pressure, it becomes warmer. This is what happens to the cold air that comes down to take the place of rising warm air. The earth is much cooler than the sun, and the wave length of the earth’ s radiations is much longer than that of sun rays. 64. These longer heat waves cannot pass through the atmosphere as easily as the short waves coming from the sun. 65. Similarly, radio stations that transmit programs to distant countries broadcast in short waves, which can travel all round the world. Stations that broadcast local programs send out longer waves, which can be received more easily, but only in a limited area.
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In 1971 there were about 3,700 million people in the world. If the population were (21) evenly over the earth’ s surface there would be about 50 people to the square mile; but there are vast areas of desert and mountain and tropical forest (22) are uninhabited, (23) at the other (24) , in the great cities millions may live within a few square miles. (25) of the world’ s population is concentrated on only a small (26) of the earth’ s land surface, in the rich valleys and (27) plains, because people up to the present time have (28) to congregate in place where the climate and soil make it easy to grow food and obtain shelter. A (29) world population and the discoveries of science (30) this pattern of distribution in the future. As men slowly learn to master diseases, control floods, prevent famines, and stop wars, fewer people die every year; and in (31) the population of the world is steadily (32) . When numbers (33) , the extra mouths must be fed. New lands must be brought (34) cultivation, or land already (35) , made to yield larger crops. In some areas the accessible land is largely so intensively cultivated (36) it will be difficult to make it (37) more food. in some areas the population is so dense that the land is divided into. units (38) tiny to allow for much improvement in farming methods. (39) a large part of this farming population drawn (40) into industrial occupations, the land might be farmed much more productively by modern methods.
Passage 3 Most scientists blame people, at least in part, for global warming. Now, some researchers say people may be partly to blame for the cooling of Antarctica as well. While average global temperatures have risen about one degree Fahrenheit over the past century, Antarctica over all appears to have cooled slightly in the past few decades. That has been puzzling, because the polar regions are thought to be more sensitive to warming trends than the rest of the globe. Even more puzzling, a small portion of Antarctica--the peninsula that stretches north toward South America--defies the cooling trend. It has been warming very rapidly, about five degrees over the past 50 years, 10 times the global average. Writing in today’ s issue of the journal Science, Dr. David Thompson, a professor of atmospheric science at Colorado State University, and Dr. Susan Solomon, a senior scientist at the National Oceanic and Atmospheric Administration in Boulder, Colo., argue that the ozone hole, which has opened up each spring over Antarctica in recent years, may help explain both contradictory trends. A vortex of winds continually blows around Antarctica, tending to trap cold air at the South Pole. In the new paper, Dr. Thompson and Dr. Solomon show that the winds have strengthened in the past few decades, keeping the cold air even more confined. The peninsula, which lies outside the wind vortex, escapes the cooling effect, the scientists said. They say the ozone hole may be the cause of the stronger winds. Close to the ground, ozone, a molecule consisting of three oxygen atoms, forms a large and unhealthy component of smog. High in the atmosphere, however, nature occurring ozone is essential for life, blocking ultraviolet rays that would fatally mangle DNA. However, fewer ozone molecules mean the atmosphere absorbs less ultraviolet radiation. Instead of warming the air, the rays bounce off the snow and ice of Antarctica and reflect back into space. Scientists already knew that the ozone hole had cooled the upper atmosphere. Dr. Thompson and Dr. Solomon show that the troposphere, the lowest six miles of the atmosphere, has also cooled. "It’ s a lot of food for thought in there," said Dr. John Walsh, a professor of atmospheric science at the University of Illinois and an author of a paper in Science in January that indicated Antarctica was cooling. He noted that the ozone hole was usually largest in November or December, but that the greatest cooling had been about six months later. Which of the following is NOT the reason for the rapid warming of the peninsula mentioned in Para. 2
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