How do greenhouse gases absorb infrared radiation and send heat back toward Earth’s surface?

Greenhouse gases—such as carbon dioxide, methane, and water vapour—absorb infrared radiation emitted from Earth’s surface through the rotations and vibrations of their chemically bonded atoms.123

Because these molecules possess specific chemical properties, they are able to capture this outgoing longwave radiation, which would otherwise escape into space. Once a greenhouse gas molecule absorbs this energy, it re-emits the radiation in all directions—upward toward space and downward back toward Earth’s surface and lower atmosphere.13

This process effectively traps heat within the atmosphere. By emitting radiation downward, these gases increase the total amount of energy directed toward the surface, forcing the Earth to maintain a higher surface temperature to achieve thermodynamic equilibrium. This mechanism, known as the greenhouse effect, is essential for maintaining a habitable climate, though human-driven increases in these gases can lead to an enhanced greenhouse effect and global warming.12