The Greenhouse Effect

If greenhouse gas molecules were enlarged, this would be their general shape. Click on image for full size version (25K JPG) NCAR/UCAR

Have you ever been inside a greenhouse on a cold winter day? It might be cold outside, but inside the greenhouse lush green plants flourish in the warmth and sunshine. Greenhouses are made of glass and are designed to hold heat inside. The atmospheres of some planets are able to trap energy just like a greenhouse. Energy from the Sun can enter the atmosphere, but not all of it can easily find its way out again.

What blocks the Sun’s energy from escaping a planet’s atmosphere? Unlike a greenhouse, planets do not have a layer of glass over them! Instead, molecules in the atmosphere called greenhouse gases absorb the heat. Greenhouse gases include water vapor, methane, ozone, nitrous oxide, and carbon dioxide.

An atmosphere that contains greenhouse gases can have a powerful greenhouse effect. Without its atmosphere and greenhouse gases, the surface of the Earth would be as cold as the surface of Mars. The presence of too many greenhouse gases can cause the temperature to increase out of control, however. Such is the case with the atmosphere of Venus.

Earth's greenhouse effect is growing stronger as the amount of greenhouse gases in the atmosphere increases. The additional greenhouse gases come mainly from burning of fossil fuels, which releases the gases and other air pollutants into the atmosphere. A stronger greenhouse effect is causing Earth's climate to warm.