BioEd Online

Teacher Background

Several transparent gases in the lower layer of the atmosphere (troposphere) have an important role in determining the temperature of Earth’s surface. These gases, which act like glass windows in a greenhouse or automobile, let light and other forms of radiation from the sun pass through the atmosphere. Much of this energy is absorbed into Earth’s surface, which becomes warmer (just like the seats in a car parked in the sun). Some heat, however, is radiated back into the atmosphere. There, gases like carbon dioxide, methane, ozone, and water vapor (the so-called “greenhouse gases”) absorb some of the heat and send it out again in all directions, including back toward the surface. This warms Earth’s surface and the lower atmosphere.

Without the warming effect of greenhouse gases, Earth’s average surface temperature would be around –18°C (0°F) instead of the actual temperature of about 15°C (59°F). Much of the planet would be frozen. However, if there were more of the greenhouse gases, Earth’s surface would be too hot to support life. Scientists around the world are concerned that increased levels of greenhouse gases (especially carbon dioxide), resulting from human activities, are causing additional warming of the planet’s surface. Levels of carbon dioxide in the atmosphere have increased more than 30% since the industrial revolution. This increase is due primarily to the burning of fossil fuels and changes in land use (burning forests to clear land for farming, for example). Even minor increases in the surface temperature can have far-reaching effects. Major climactic patterns of winds, temperature, and rainfall could change drastically, impacting water resources, coastlines, agriculture, forests, and energy production, as well as patterns of disease.

This activity is designed to provide a simple introduction to the concepts underlying the greenhouse effect as well as background information for thinking about climate change.

Objectives and Standards

Concepts

• Different materials absorb and trap heat differently.

• Some materials allow light to pass through but do not let heat escape.

Science, Math, and Health Skills

• Predicting

• Observing

• Modeling

• Drawing conclusions

Materials and Setup

Materials per Group of Students

• 4 chocolate candies (“kisses” or squares)

• four 9-oz clear plastic cups

• 4 plain round cookies

• 4 toothpicks

• 1/4 cup of marshmallow creme (or frosting)

• plastic knife or spreader

• sheet of aluminum foil (approx. 12-in. sq. or 30-cm sq.)

• sheet of black construction paper, 9 in. x 12 in.

• sheet of white construction paper, 9 in. x 12 in.

• tape or a stapler

• tray or paper plate

Setup

1. Place all materials in a central area for Materials Managers to collect for their groups. Have students work in groups of 4.

2. If you are teaching this lesson during the winter, you will need to conduct it indoors with a heat lamp or use a sunny window. When the weather is warm, students may conduct the experiment outside in an area that is protected from the wind.

Procedure and Extensions

1. Ask students, Have you ever noticed how warm a car can become when it is parked in the sun? Where do you think the heat inside the car comes from? How do you think we can learn more about light and heat?

2. Tell students that they will investigate the heat-trapping qualities of different materials by using the sun to make a treat (see “Greenhouse S’mores,” left sidebar). Have Materials Managers collect the four cups and one sheet of each of the three coverings for their groups. Have students make the following covers for three of the cups: white construction paper, black construction paper, and aluminum foil. All covers should be about the same size and shape. Have students follow the instructions described at left OR challenge students to create their own cover designs. One cup will not have a cover.

3. After students have made covers for three cups, have each Materials Manager pick up four round cookies, four chocolate candies, a spreader, and a small container of marshmallow creme or frosting.

4. Ask students if they have ever made s’mores using marshmallows and chocolate squares. Tell students they will be using solar energy to make s’mores in class. Each student will create one s’more by placing a small amount of marshmallow creme or frosting on the cookie, followed by a chocolate candy.

5. Direct students to place the cookies on a plate or tray and to cover each cookie with one of the cups. (If the experiment will be conducted outside, have students tape the cups to the plate.)

6. Within their groups, have students discuss the cover treatments and predict which treatment will result in the most softened or melted chocolate. Have students rank their predictions using a scale of 1 to 4, in which 1 = least softened and 4 = most softened.

7. Have students place the plates and cups in a sunny spot near a window or outside in direct sunlight, preferably on a lawn. (Do not place the plates on hot pavement in the sun. The heat from the already warm surface will affect the results.)

8. Let students make their first observations after about 15 minutes. They should use a toothpick to test the candies. Depending on the air temperature, some of the chocolate candies may begin to soften by this time. Continue observing at 10–15 minute intervals until at least one of the candies has become very soft. (Note: some chocolate candies may retain their shape even when they are very soft.)

9. Have students bring their plates indoors and observe the condition of each of the four chocolate candies. Ask students to rank the candies from least melted to most melted—giving a score of “1” to the least softened or melted and a score of “4” to the most softened or melted.

10. Make a chart on the board (see example, PDF) and have each group report its results.

11. Add (or have students add) all of the points received by each treatment. Usually, the clear/ uncovered cup treatment will end up with the most points (clear cups result in the most melted chocolate, followed by the white cover and the black cover). The foil cover will have the fewest points (least melted chocolate). Because the observations are subjective, there usually will be some discrepancies among the results reported by each group. Use this as an opportunity to point out the importance of conducting an experiment more than once.

12. Discuss the results with the class. Ask, Which treatment melted the chocolate the most? The least? Why do you think so? Help students understand that more light energy was able to pass into the clear cup than into the others. Much of this energy was transformed into heat. The cup covered with foil reflected more light energy away. The white paper reflected some of the light energy away. The black paper absorbed more energy than the white cup.

13. Let each student eat his or her s’more while you lead a discussion connecting their observations to what happens inside a car parked in the sun. You also may want to refer to page 9 in the Global Atmospheric Change unit's storybook, Mr. Slaptail’s Curious Contraption. Help students understand that certain gases in the atmosphere, especially carbon dioxide, act like the clear cups in their experiments. These gases keep the surface of the planet warmer than it would be otherwise.

Extension

Before beginning, have students create a class chart of their predictions about the results of the investigation. Compare the predictions to the results and discuss the differences with students.

Handouts and Downloads