Name Class Date CHAPTER 15 The Atmosphere SECTION 2 Atmospheric Heating BEFORE YOU READ After you read this section, you should be able to answer these questions: • How does energy travel from the sun to Earth? • What are the differences between radiation, conduction, and convection? • Why is Earth’s atmosphere so warm? How Does Energy Travel from the Sun to Earth? Most of the heat energy on Earth’s surface comes STUDY TIP from the sun. Energy travels from the sun to Earth by Outline In your notebook, radiation, which means that it travels through space as write an outline of this chap- ter. Use the questions in bold waves. As solar energy (energy from the sun) is absorbed to make your outline. As you by air, water, and land, it turns into heat energy. This read, fi ll in information about energy causes winds, the water cycle, ocean currents, each question. and changes in the weather. What Happens to Radiation from the Sun? Not all of the radiation from the sun reaches Earth’s surface. Much of it gets absorbed by the atmosphere. Some of it is scattered and reflected by clouds and gases. About 25% is TAKE A LOOK scattered and 1. Identify How much of the reflected by sunlight that gets to Earth is clouds and air. absorbed by Earth’s surface? About 20% is absorbed by ozone, clouds, and atmospheric gases. 2. Summarize What happens to the sunlight that is not absorbed by Earth’s surface? About 50% is absorbed by Earth’s surface. About 5% is reflected by Earth’s surface. Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Textbook 285 The Atmosphere Name Class Date SECTION 2 Atmospheric Heating continued How Is Heat Transferred by Contact? Once sunlight is absorbed by Earth’s surface, it is converted, or changed, into heat energy. Then, the heat can be transferred to other objects and moved to other places. When a warm object touches a cold object, heat moves from the warm object to the cold one. This move- ment of heat is called thermal conduction. When you touch the sidewalk on a hot, sunny day, heat energy is conducted from the sidewalk to you. The same thing happens to air molecules in the atmosphere. When READING CHECK they touch the warm ground, the air molecules heat up. 3. List Name two ways that air gets heated. How Is Heat Energy Transferred by Motion? If you have ever watched a pot of water boil, you have seen convection. During convection, warm material, such as air or water, carries heat from one place to another. When you turn on the stove under a pot of water, the Critical Thinking water closest to the pot heats up. As the water heats up, its density decreases. The warm water near the pot is not 4. Apply Concepts Before the water in the pot can heat as dense as the cool water near the air. Therefore, the up, the pot itself must heat cool water sinks while the warm water rises. up. Does the pot heat up As it rises, the warm water begins to cool. When it by conduction, convection, or radiation? Explain your cools, its density increases. It becomes denser than the answer. layer below, so it sinks back to the bottom of the pot. This forms a circular movement called a convection current. Convection currents also move heat through the atmosphere. In fact, most heat energy in the atmosphere is transferred by convection. Air close to the ground is heated by conduction from the ground. It becomes less dense than the cooler air above it. The warmer air rises while the cooler air sinks. The ground warms up the cooler air by conduction, and the warm air rises again. Convection Current Warm air cools down. Warm, less Cooler, TAKE A LOOK dense air denser 5. Describe What happens rises. air sinks. to warm air as it moves through the atmosphere? Cool air warms up. Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Textbook 286 The Atmosphere Name Class Date SECTION 2 Atmospheric Heating continued How Does the Earth Stay Warm? A gardener who needs to keep plants warm uses a glass building called a greenhouse. Light travels through the glass into the building, and the air and plants inside absorb the energy. The energy is converted to heat, which cannot travel back through the glass as easily as light came in. Much of the heat energy stays trapped within the greenhouse, keeping the air inside warmer than the air outside. Earth’s atmosphere acts like the glass walls of a green- house. Sunlight travels through the atmosphere easily, but heat does not. Gases in the atmosphere, such as water vapor and carbon dioxide, absorb heat energy coming from Earth. Then, they radiate it back to Earth’s surface. This is known as the greenhouse effect. READING CHECK The Greenhouse Effect 6. List Name two gases in Earth’s atmosphere that 1. Light energy from the absorb heat. sun passes through the atmosphere and is absorbed Sun by clouds and by Earth’s surface. 2. Clouds and Earth’s surface TAKE A LOOK radiate the energy back out as 7. Identify On the drawing, heat energy. label the light coming from the sun with an L. Label the heat energy that is trapped by Earth’s atmosphere with Earth an H. 3. Heat energy warms Earth’s atmosphere. What Is Global Warming? Many scientists are worried that Earth has been getting warmer over the past hundred years. This increase in tem- peratures all over the world is called global warming. Scientists think that human activities may be causing global warming. When we burn fossil fuels, we release Say It greenhouse gases, such as carbon dioxide, into the Predict How might global atmosphere. Because greenhouse gases trap heat in the warming affect your community? What can you atmosphere, adding more of them can make Earth even do to slow global warming? warmer. Global warming can have a strong effect on In groups of two or three, weather and climate. discuss how global warming might affect your lives. Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Textbook 287 The Atmosphere Name Class Date Section 2 Review SECTION VOCABULARY convection the transfer of thermal energy by the radiation the transfer of energy as electro- circulation or movement of a liquid or gas magnetic waves global warming a gradual increase in average thermal conduction the transfer of energy as global temperature heat through a material greenhouse effect the warming of the surface and lower atmosphere of Earth that occurs when water vapor, carbon dioxide, and other gases absorb and reradiate thermal energy 1. Apply Concepts A person is camping outside. The person toasts a marshmallow by holding it above the flames of the fire. Does the marshmallow cook because of convection, conduction, or radiation? Explain your answer. 2. Compare Fill in the table below to name and describe the three ways energy is transferred in Earth’s atmosphere. Type of energy transfer How energy is transferred Energy travels as electromagnetic waves. Conduction 3. Explain How does most of the heat in Earth’s atmosphere move from place to place? 4. Identify Relationships Explain how global warming and the greenhouse effect are related. Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Textbook 288 The Atmosphere Earth Science Answer Key continued 4. the pressure produced by the air above a 4. Conduction, because heat is transferred surface between two objects that are touching. 5. The air pressure is higher around the tree 5. It rises and cools. than around the plane. 6. water vapor and carbon dioxide 6. Air temperature in the atmosphere can 7. L should be on a short-wavelength ray; H increase or decrease with altitude. should be on a long-wavelength ray. 7. about 80 km 8. People and other living things live in the Review troposphere. It is where weather happens. 1. Possible answers: radiation, because the 9. It differs from place to place. heat moves as waves through the air to the marshmallow; convection, because hot 10. It absorbs harmful ultraviolet energy. air carries energy from the fire toward the 11. because the temperatures are so high there marshmallow 12. Layer How Important 2. Type of energy How energy is transferred temperature features transfer and pressure change as you Radiation Energy travels as electromagnetic move higher waves. Troposphere Temperature This densest Convection Heat circulates; warm air rises decreases; layer contains and cool air sinks. pressure most of the Conduction Heat moves from warm objects decreases. atmosphere. to cold objects. Weather and clouds are here. 3. The heat moves by convection. Warm air Stratosphere Temperature Gases are rises and cools off. Cool air sinks and then increases; arranged warms up. The air is constantly moving. pressure in layers; it decreases. contains the 4. Global warming can be caused by the ozone layer. greenhouse effect. The greenhouse effect Mesosphere Temperature It has the lowest causes Earth’s air temperature to increase. decreases; temperatures. pressure decreases. SECTION 3 GLOBAL WINDS AND LOCAL Thermosphere Temperature It has auroras WINDS increases; and the highest pressure temperatures. 1. moving air caused by differences in air decreases. pressure Review 2. H should be inside the balloon; L should be outside the balloon. 1. Possible answer: the gases that cover the surface of a body in space 3. Some parts of Earth get more energy from the sun than others. 2. Different layers are made of different gases. Different gases absorb different amounts of 4.