Greenhouse effect

The term greenhouse effect is used to discuss gases which trap heat, and raise the temperature of Earth's atmosphere.

The term comes from how the glass walls and roofs of greenhouses. Glass is transparent to visible light. Visible light heats the things inside a greenhouse. If the things inside the greenhouse were not under glass those items would radiate that heat away, as infrared light. But, because glass is opaque to infrare light, that heat is trapped.

Carbon Dioxide is called a greenhouse gas because, like glass, it too is transparent to visible light and opaque to infrared. Methane is another greenhouse gas.