If the transmission of solar radiation to the surface of a planet is less attenuated than the emission of thermal (heat) radiation from the surface to space, the surface and the lower atmosphere of the planet warm until emission at the top of the atmosphere balances (in a multi-year average) the amount of solar radiation absorbed by the atmosphere and the surface. For the planet Earth the warming at the surface because of strong absorption of thermal radiation by some atmospheric gases is caused nearly exclusively by minor constituents, i.e. by less than three per mille of the mass of the atmosphere. The warming caused by these minor constituents is about 30°C. The use of the word "about" is due to the fact that we do not know which reflectivity for solar radiation the Earth's surface would have without these gases, as the ocean might not exist as at present. Since the heat absorbing gases act like glass covering a greenhouse, the warming effect caused by them is called in the rough analogy greenhouse effect.
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