The Greenhouse EffectEarth's atmosphere acts like a greenhouse, warming our planet in much the same way that an ordinary greenhouse warms the air inside its glass walls. Like glass, the gases in the atmosphere let in light yet prevent heat from escaping. This natural warming of the planet is called the greenhouse effect.
Greenhouse gases-carbon dioxide, methane, nitrous oxide, and others-are transparent to certain wavelengths of the Sun's radiant energy, allowing them to penetrate deep into the atmosphere or all the way to Earth's surface. Clouds, ice caps, and particles in the air reflect about 30 percent of this radiation, but oceans and land masses absorb the rest, then release it back toward space as infrared radiation. The greenhouse gases and clouds effectively prevent some of the infrared radiation from escaping; they trap the heat near Earth's surface where it warms the lower atmosphere. If this natural barrier of atmospheric gases were not present, the heat would escape into space, and Earth's mean global temperatures could be as much as 33 degrees Celsius cooler [about -18 degrees Celsius as opposed to 15 degrees Celsius].
Over the centuries, the concentration of greenhouse gases, especially carbon dioxide, has fluctuated naturally, and the greenhouse effect has moderated the temperature of Earth accordingly. Now, our efforts to provide for Earth's growing population are releasing greenhouse gases into the atmosphere at rates greater than any other phenomena. As we burn fossil fuels, clear forests, and continue to use gasoline-dependent transportation, we increase the level of carbon dioxide in the atmosphere. As a result, we continue to harm Earth's atmosphere.
Updated January 24, 1996. Contacts