The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without this atmosphere.

By their percentage contribution to the greenhouse effect on Earth the four major gases are:

water vapor, 36–70%

carbon dioxide, 9–26%

methane, 4–9%

ozone, 3–7%

It is not possible to assign a specific percentage to each gas because the absorption and emission bands of the gases overlap (hence the ranges given above). Clouds also absorb and emit infrared radiation and thus affect the radiative properties of the atmosphere

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