Search for individual gases in combination with the greenhouse effect ("methane greenhouse," for example). There are numerous articles. R stands for Research Update and E stands for Encyclopedia article. Includes graphs and other illustrations.
This course site provides an explanation and illustrations of the greenhouse effect. The contents are along the left, and you'll find that chapter 3.0 (The Greenhouse Gases) has sections on the effect of carbon dioxide and methane in particular.
Information covering all aspects of human impact on the environment from scholarly, governmental, and general-interest sources. Topics include global warming, green building, pollution, waste and recycling, renewable energy, and more.