What are examples of greenhouse gases and what are their sources?
A greenhouse gas is a gas that is transparent to visible light but opaque to infrared light.
As sunlight enters the atmosphere it is short wave radiation. Greenhouse gases allow shortwave radiation to pass through them. When the sunlight hits the Earth it warms the Earth. As a result of this the warmed Earth emits heat or long wave radiation. Greenhouse gases are not transparent to energy of this wave length so they trap the heat.
The reason they are called greenhouse gases is because they work like the windows of a greenhouse works, allowing the sunlight to enter but trapping the heat inside.