CHAPTER Why It Matters Climate affects where and how Climates of people live. An understanding of Earth’s climates and the factors, both physical and human, that influence them adds to a more the Earth complete view of life on Earth. Section 1: Earth-Sun Relationships The physical environment affects people and their activities. Earth’s position in relation to the sun affects temperatures, day and night, and seasons on Earth, which in turn influ- ence when and how people perform certain activities. Section 2: Factors Affecting Climate Physical processes shape Earth’s surface. Latitude, elevation, wind patterns, and ocean currents affect Earth’s climates. Section 3: World Climate Patterns Geographers organize Earth into regions that share common char- acteristics. Geographers classify Earth’s climate and vegetation into regions. Geography ONLINE Chapter Overview Visit the World Geography and Cultures Web site at glencoe.com and click on Chapter Overviews—Chapter 3 to preview infor- mation about planet Earth. Monaco Glacier, Svalbard, Norway, is a popular hunting ground for polar bears. 48 Unit 1 Hans Strand/CORBIS Identifying Make a Vocabulary Book to help you organize and learn the content vocabulary terms intro- duced as you read about the climates of the Earth. You may need to make more than one Vocabulary Book. Reading and Writing As you read the chapter, write a THE WORLD term on each tab and its definition underneath. You may want to illustrate visual terms such as rain shadow. Chapter 3 49 SECTION 1 Earth-Sun Guide to Reading Section Preview Relationships Earth’s position in relation to the sun affects temperatures, day and From the Alps in the heart of Europe, scientists gather night, and seasons on Earth. data about melting glaciers and changes in the snow Content Vocabulary line. Their research reveals information about the • weather (p. 51) • equinox (p. 51) Earth’s atmosphere and the warming effects of the sun. • climate (p. 51) • solstice (p. 51) Such dynamic relationships between the Earth and the • axis (p. 51) • greenhouse • temperature effect (p. 52) sun influence all life on Earth. (p. 51) • global warming • revolution (p. 53) Voices Around the World (p. 51) Academic Vocabulary “We marvel at the mountains, but it’s the water that everything depends on. • contrast (p. 51) . Snow, glaciers, permafrost, surging hot springs, aquamarine ramparts of • affects (p. 51) ice — the very capillaries of the rock itself are permeated with water. It comes • regulated (p. 52) sleeking down black rock faces, it drips into hidden cavern pools. If the Alps Places to Locate had a voice, it would be the musical notes of water. Water is what is literally • Tropic of Cancer (p. 51) holding the high mountains together, and if the ice and permafrost begin to • Tropic of Capricorn (p. 52) lose their grip, as is already happening, the mountains start to crumble.” Reading Strategy — Erla Zwingle, “Meltdown: The Alps Under Pressure,” Categorizing Complete a graphic National Geographic, February 2006 organizer similar to the one below by listing the major characteristics of the summer and winter solstices. Northern Hemisphere Summer solstice Winter solstice • • • • • • • • Hikers in the Alps 50 Unit 1 Hans Strand/CORBIS Climate and W eather MMAINAIN IIdeadea The relationship between the Earth and the sun affects climate, which influences life on Earth in dramatic ways. GEOGRAPHY AND YOU Did you know that as you are sitting in geography class it is nighttime in some parts of the world? Read to learn how the Earth-sun relationship causes night and day. Climate is often confused with weather, which is a short-term aspect of climate. Weather is the condition of the atmosphere in one place during a limited period of time. When people look out the window or watch the news to see whether they need umbrellas or sunscreen, they are checking the weather. Climate is the term for the weather patterns that Earth’s Revolution an area typically experiences over a long period of While planet Earth is rotating on its axis, it is time. People in Seattle, Washington, for example, also traveling in an orbit around the sun, our near- frequently use umbrellas because of the rainy, wet est star. It takes the Earth a few hours more than climate. In contrast, people in the dry, desert 365 days — one year — to complete one revolution, climate of Phoenix, Arizona, must use sunscreen or trip around the sun. to protect themselves from the sun. The Earth’s revolution and its tilt cause changes in the angle and amount of sunlight that reach different locations on the planet. These changes THE WORLD Earth’s Tilt and Rotation follow a regular progression known as the sea- Earth’s tilt is one reason for variations in sun- sons. During the course of a year, people on light. As the diagram above shows, the Earth’s most parts of the Earth experience distinct dif- axis — an imaginary line running from the North ferences in the length of days and the daily tem- Pole to the South Pole through the planet’s cen- perature as the seasons change. ter— is currently tilted at an angle of about The seasons are reversed north and south of 23½°. Because of the tilt of this axis, not all the Equator. When it is spring in the Northern places on the planet receive the same amount of Hemisphere, it is fall in the Southern Hemisphere. direct sunlight at the same time. When it is winter in the Southern Hemisphere, it For this reason, the angle of tilt affects the is summer in the Northern Hemisphere. Around temperature — the measure of how hot or cold a March 21, the sun’s rays fall directly on the place is. Areas that receive a large amount of direct Equator. This day is called an equinox (meaning sunlight have warmer temperatures than places “equal night”) because daylight and nighttime that receive little direct sunlight. Temperature is hours are equal. usually measured in degrees on a set scale. The most common scales for measuring temperature The Tropics of Cancer and Capricorn As the Earth are Fahrenheit (°F) and Celsius (°C). continues its revolution around the sun, it moves Whether or not a particular place on Earth so that eventually the sun’s rays directly strike the receives light also depends on the side of the Tropic of Cancer at 23½° N, the northernmost planet that is facing the sun. Earth rotates on its point on the Earth to receive the direct rays of the axis, making one complete rotation every 24 sun. These direct rays reach the Tropic of Cancer hours. Rotating from west to east, the Earth about June 21, bringing the Northern Hemisphere turns first one hemisphere and then the other its longest day of sunlight. This date, known as toward the sun, alternating between the light of the summer solstice, marks the beginning of sum- day and the darkness of night. mer in the Northern Hemisphere. Chapter 3 51 By about September 23, the Earth has revolved so that the sun’s rays directly strike the Equator The Greenhouse Effect again. This equinox marks the beginning of fall in the Northern Hemisphere. Gradually the sun’s MMAINAIN IIdeadea The natural process of the greenhouse direct rays strike farther south, reaching their effect has been influenced by human activity. southernmost latitude of 23½° S, at the Tropic of GEOGRAPHY AND YOU Have you heard news Capricorn about December 22. The winter sol- accounts of the dangers of global warming? Read to stice is the day of shortest daylight in the Northern learn how global warming can affect Earth. Hemisphere, beginning the season of winter. The Poles The most dramatic variation in the Even on the sunniest days in the warmest cli- amount of sunlight occurs at the Poles. For six mates, only part of the sun’s radiation passes months of the year, one Pole is tilted toward the through the Earth’s atmosphere. The atmosphere sun and receives continuous sunlight, while the reflects some radiation back into space. Enough other Pole is tilted away from the sun and radiation, however, reaches the Earth to warm receives little to no sunlight. the land, water, and air. At the North Pole, the sun never sets from Because the atmosphere traps some heat and about March 20 to September 23. At the South keeps it from escaping back into space too Pole, continuous daylight lasts from about quickly, Earth’s atmosphere is like the glass in a September 23 to March 20. The tilt of the Earth’s greenhouse — it traps the sun’s energy for grow- axis as it revolves around the sun causes this natu- ing plants even in cold weather. Without this ral phenomenon, known as the midnight sun. The greenhouse effect, the Earth would be too cold occurrence of the midnight sun goes almost unno- for most living things. ticed in sparsely populated Antarctica. Parts of In order to support plant growth, conditions northern North America (including Alaska) and in a greenhouse must be regulated. If too much northern Europe in the Arctic, however, have become popular tourist destinations as lands of the midnight sun. Regions What factor distin- 1. Regions Why are the seasons reversed in the guishes weather from climate? Northern and Southern Hemispheres? 2. Place Explain the difference between the equinoxes and the solstices. The Earth’s Seasons Use StudentWorks™ Plus or glencoe.com. 52 Unit 1 heat escapes, the plants will freeze. If too much heat is trapped, the plants will wilt or dry out. The greenhouse effect of Earth’s atmosphere fol- lows some of the same general rules.