Greenhouse gases are gases in the Earths atmosphere that trap heat, creating a greenhouse effect that results in global warming and climate change. They let sunlight pass through the atmosphere, but they prevent the heat that the sunlight brings from leaving the atmosphere. The most abundant greenhouse gas is water vapor, but other important greenhouse gases include carbon dioxide, methane, nitrous oxide, and ozone. Greenhouse gases absorb the infrared radiation that the Earth emits, resulting in the warming of the planets surface.

Carbon dioxide is the primary greenhouse gas emitted through human activities, accounting for 79% of all U.S. greenhouse gas emissions from human activities. Methane and nitrous oxide are also significant greenhouse gases. Industrial gases such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3) are exclusively human-made and are also potent greenhouse gases.

Greenhouse gases are transparent to incoming (short-wave) radiation from the sun but block infrared (long-wave) radiation from leaving the Earths atmosphere. As concentrations of these gases increase, more warming occurs than would happen naturally. While greenhouse gases are a good thing and necessary for life on Earth, scientists are concerned that human activities are adding too much of these gases to the atmosphere, leading to global warming and climate change.