Hot Box: What is the Greenhouse Effect?
What is the greenhouse effect?
- 2 thermometers
- Colorless plastic food wrap timer
- Half fill the shoebox with soil.
- Lay one of the thermometers on the surface of the soil. Keep the second thermometer outside of the box.
- Cover the opening of the box with a single layer of plastic wrap.
- Take a reading from both thermometers.
- Place the box and second thermometer side by side in a sunny place outdoors.
- Record readings from both thermometers every 15 minutes for one hour.
- Record readings every hour thereafter for 4 hours.
Allor most all of the temperature readings show that the temperature inside the plastic-covered box was higher than the temperature outside the box.
A structure designed to provide a protected, controlled environment for raising plants indoors is called a greenhouse. It is made of glass or other material that allows the sun's light to pass through. The box in this experiment is an example of a greenhouse.
Solar energy is electromagnetic radiation. This energy is emitted by the Sun and comes in the form of waves of varying wavelengths. The short-wavelength radiation from the Sun passes freely through the plastic wrap covering the box. Most of this energy is absorbed by the soil and cardboard sides of the box, causing them to heat up. Long-wavelength radiation, called infrared radiation (heat waves), is then released by the soil and the cardboard sides.
Some scientists think that short-wavelength radiation enters the box through the plastic and changes into long-wavelength radiation, or heat waves, which are then trapped inside by the plastic. Other scientists believe that because greenhouses are closed, heated air becomes trapped inside. Since no cooling air can enter the box, the temperature inside the greenhouse increases.
The Earth's atmosphere, however, does trap the long-wavelength radiation. The composition of gases in air is about 78 percent nitrogen, 21 percent oxygen, and 1 percent water vapor, carbon dioxide, and other gases such as neon, sulfur dioxide, and carbon monoxide. Like the plastic over the box in this experiment, the atmosphere allows solar energy to pass through to the Earth's surface. The surface heats up and gives off long-wavelength radiation. Most of these heat waves are absorbed by water vapor (water in its gas phase) and carbon dioxide (gas produced by burning fuels and exhaled by animals) in the lower atmosphere. These atmospheric gases reemit a large portion of the heat waves back toward the Earth, which causes the Earth's surface to gradually become warmer. The greenhouse and the atmosphere both trap warmth from the Sun. For this reason, this warming of the Earth is called the greenhouse effect.
- Does the type of cover on the box affect the results? Repeat the original experiment, preparing boxes with different covers. One can be covered with glass. Ask an adult to remove a piece of glass from a picture frame and to place masking tape around the edges. Cover other boxes with transparent plastic report folders of various colors. Science Fair Hint: Display samples of the box covers with the results of the experiment.
- Do surface structures affect the results? Repeat the original experiment, preparing several boxes. Cover the surface of the soil in the boxes with different materials, such as rocks, leaves, and grass. Science Fair Hint: Display photographs of the various boxes with the results of the experiment.
- Design ways to cover the box so that you can determine if it is the lack of air circulation or the trapped heat rays that affect the temperature change.