The greenhouse gas effect is caused by certain gases trapping energy in the atmosphere and making the Earth warmer. The greenhouse effect is important. Without the greenhouse effect, the Earth would not be warm enough for humans to live. But when the greenhouse too many greenhouse gases are released into the atmosphere the effect becomes stronger and makes the Earth warmer than usual. Even a little extra warming may cause problems for humans, plants, and animals. Greenhouse gases include water vapor, carbon dioxide, nitrous oxide, methane, hydrofluorocarbons, perfluorocarbons and sulfur hexaflouride.

Additional Resources

http://www.epa.gov/climatechange/emissions/index.html

http://www.epa.gov/climatechange/kids/greenhouse.html