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How does the natural greenhouse effect keep Earth warm enough for life?
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Earth
A composite image of Earth captured by instruments aboard NASA's Suomi National Polar-orbiting Partnership satellite, 2012.
The natural greenhouse effect is a vital process that maintains Earth's surface temperature, keeping the planet habitable. Without this background effect, Earth would be approximately 33 °C (59 °F) colder and likely a frozen, uninhabitable world.12
The process functions through the following mechanism:
- Absorption of Terrestrial Radiation: Earth’s surface absorbs incoming solar energy and reradiates it back toward space as long-wave infrared radiation.12
- Role of Greenhouse Gases: Certain trace gases in the atmosphere—primarily water vapour, carbon dioxide, and methane—absorb this outgoing infrared radiation.123
- Reradiation: Because these greenhouse gases emit the radiation they absorb equally in all directions, a significant portion is directed back toward Earth’s surface and lower atmosphere.13
- Surface Warming: This downward emission increases the total energy retained near the surface, necessitating a higher surface temperature to maintain [thermodynamic equilibrium].1
It is important to distinguish this essential natural process from the "enhanced" greenhouse effect, which is driven by human activities that increase the concentration of these gases beyond natural levels.1