What Factors Impact a Greenhouse?

Modified with permission from Global Climates - Past, Present, and Future, S. Henderson, S. Holman, and L. Mortensen (Eds.). EPA Report No. EPA/600/R-93/126, U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC 47 - 52.

Background

The earth's atmospheric "greenhouse effect" is much more complex than the simple greenhouse experiment described in Activity 12. While the earth's temperature is dependent upon the greenhouse-like action of the atmosphere, the amount of heating and cooling are strongly influenced by several factors.

The type of surface that sunlight first encounters is the most important factor. Forests, grasslands, ocean surfaces, ice caps, deserts, and cities all absorb, reflect, and radiate radiation differently. Sunlight falling on a white glacier surface strongly reflects back into space, resulting in minimal heating of the surface and lower atmosphere. Sunlight falling on a dark desert soil is strongly absorbed, on the other hand, and contributes to significant heating of the surface and lower atmosphere. Cloud cover also affects greenhouse warming by both reducing the amount of solar radiation reaching the earth's surface and by reducing the amount of radiation energy emitted into space.

Scientists use the term albedo to define the percentage of solar energy reflected back by a surface. Understanding local, regional, and global albedo effects is critical to predicting global climate change. The following are some of the factors that influence the earth's albedo.

In this exercise, students will form their own conclusions as to how different surface and cover types affect heating using the model bottle systems introduced in Activity 12.

Learning Goals

  1. Students will be able to identify at least three factors affecting the heat-trapping ability of a greenhouse, including the transparency of the greenhouse cover, color of the surfaces inside the greenhouse, and type of surfaces inside.

  2. Students will be able to explain the factors important in the atmosphere's heat trapping ability.

  3. Students will understand the influence of albedo on earth's temperature.

Alignment to National Standards

National Science Education Standards

Benchmarks for Science Literacy, Project 2061, AAAS


Grade Level/Time

Materials for Each Team of Four Students

Procedure

  1. To save time, you (or your students) should prepare the model greenhouses prior to class. For each team of four students, you will need six experimental chambers. Paint the upper third of three of the bottles white.



  2. Label the bottles A, B, C, D, E, and F with bottles B, D, and F having the white paint.

  3. Fill the base of bottles A and B with dark soil, bottles C and D with white sand, and bottles E and F with room-temperature water.

  4. Tape a thermometer (using transparent tape or light-colored masking tape) to the inside of each bottle (facing out).

  5. Place the bottle tops in the bases. Make sure the bottles are capped.

  6. Make sure the bulbs of the thermometers are just above the top of the bases. If the bulbs are below the base, the thermometer may record the heat absorbed directly by the soil or water, complicating the results.

  7. Ask students to predict which bottle will get hotter. Why? Record predictions.

  8. Have each team set up a graph of time (in minutes) vs. temperature to record their observations.

  9. Each student should have a specific responsibility during the experiment, either keeping track of the time or recording the temperature for the different bottles.

  10. Place the bottles approximately six inches away from the lamp with the thermometer facing away from the light. Record the baseline temperatures.



  11. Turn on the light and begin recording the temperatures every two minutes. Continue for at least 20 minutes.

Cautionary Note: If your lamp is not big enough, six bottles may be too many to have under the light at the same time. The ones further from the light may not get the same intensity of heat as the bottles closer to the light thereby compromising the experiment. You may have the students use a sub-set of the bottles at one time. If you make changes in the experiment, make sure you also change the student guide.

Observations and Questions

  1. Compare the graphed information from the different bottles.

  2. Discuss the results and propose some possible explanations.

  3. Relate the factors affecting the model greenhouses to the factors affecting the "global greenhouse." Which factors are the same? Which are different?

Assessment Ideas

Modifications for Alternative Learners

When you're finished with the activity, click on To Student Guide or Back to Activities List at the top of the page to return to the activity menu.