Editing Earth's Energy Budget (section)

== Outgoing Thermal Radiation (Longwave) ==

To maintain thermodynamic equilibrium, the 240 W/m2 of solar energy absorbed by the planet must eventually find its way back out to space. 

Because the Earth is much cooler than the Sun, it cannot emit high-energy visible light. Instead, the warmed surface and atmosphere radiate energy outward in the form of low-energy, '''longwave radiation''' (thermal infrared). 

This is where the atmosphere acts as an insulating blanket. While the atmosphere is mostly transparent to incoming shortwave radiation, greenhouse gases (such as CO2, CH4, and N2O) are highly opaque to outgoing longwave radiation. These trace gases absorb the upward-traveling infrared energy and re-radiate it in all directions. A significant portion is directed back down to the surface, further heating the lower atmosphere. Eventually, the energy makes its way to the top of the atmosphere and escapes into space, but the presence of greenhouse gases delays this escape, maintaining the planet's habitable baseline temperature.