The Greenhouse Effect
Heat Transfer in the Atmosphere
The gases in the Earth's atmosphere are warmed by heat radiated from the Earth's surface. These warmed gases surround the Earth and act like a blanket, keeping the Earth warm.
In this project, you will demonstrate the greenhouse effect. You will discover how materials of the Earth's surface affect the greenhouse effect. You will examine the relationship between the greenhouse effect and surface temperatures at night. You will determine how composition and density of the atmosphere affect its ability to trap infrared energy. You will also show how cloud cover affects the surface temperatures at night.
Purpose: To demonstrate the greenhouse effect.
- two shoe boxes
- two thermometers
- colorless plastic food wrap
- Cover the bottom of each shoe box with about 2 inches (5 cm) of soil.
- Lay a thermometer on the surface of the soil in each box.
- Cover the opening of one box with a single layer of plastic wrap. Leave the other box uncovered.
- Take readings from both thermometers.
- Place both boxes side by side in a sunny place outdoors (see Figure 42.1).
- Record readings from both thermometers every 15 minutes for 1 hour.
The temperature readings show that the temperature inside the plastic-covered box was higher and increased faster.
Radiation, also called radiant energy, can move through space, and is not carried by matter. Radiation is also a term for the process by which this energy is transmitted. Solar energy is radiant energy from the Sun. Solar energy contains all the different forms of radiant energy, but most of the solar energy reaching Earth consists of ultraviolet radiation (causes skin to tan or even burn), visible light (radiant energy that can be seen and is divided into the rainbow colors of red, orange, yellow, green, blue, indigo, and violet), and infrared radiation (energy in the form of heat given off by all hot bodies).
Radiant energy from the Sun passes through the Earth's atmosphere and reaches the Earth's surface. However, about 30% of the Sun's total radiant energy reaching the Earth is reflected back into space by the atmosphere, the clouds, and the Earth's surface. About 20% is absorbed by the atmosphere, and the remaining 50% is absorbed by the Earth's surface. The radiant energy absorbed by Earth warms its surface, and this warm surface in turn warms the atmosphere above it. An object is warm because of its internal energy, which is also called its thermal energy. Thermal energy is the sum of all kinetic energy (energy possessed by an object because of its motion) and potential energy (stored energy of an object due to its condition or position) of particles in random motion making up an object. The faster the particles are moving, the hotter the object. Heat is the transfer of thermal energy from one object or region to another due to differences in temperature. The three methods by which heat is transferred from one place to another are: conduction, radiation, and convection. Conduction (also called thermal conduction) is the method of transferring heat by the collision of one moving molecule with another. Conduction requires physical contact between the bodies or portions of bodies exchanging heat, but radiation does not require contact or the presence of any matter between the bodies. The method of heat transfer called radiation is the transfer of heat in the form of infrared radiation. Convection is the method of transferring heat by the movement of a heated fluid. Carbon dioxide and water vapor are gases in the atmosphere that help keep heat from being lost to space. They absorb heat from the Earth and then re-emit infrared radiation, some of which strikes and is absorbed by the Earth. Like the plastic covering that prevents the escape of some of the infrared radiation emitted from the soil, as well as the heated air (mixture of gases in Earth's atmosphere) inside the closed bowl, the Earth's atmosphere keeps the Earth warm. The absorption of infrared energy by the atmosphere and Earth, called the greenhouse effect, maintains a temperature range on Earth that is hospitable to life. The term greenhouse effect comes from the fact that the atmosphere is similar to a greenhouse in that it helps warm the Earth's surface by trapping infrared energy and heated air.