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Artwork illustrating the greenhouse effect. The greenhouse effect is a process by which the Earth warms up. It occurs naturally, but there are concerns that human activities may be increasing its effect, leading to global warming. The surface of the Earth absorbs some solar radiation, reflects some, and re-radiates some at a longer (infrared, IR) wavelength. Naturally some of this IR passes through the atmosphere back into space, but the build-up of some chemicals in the atmosphere can change its absorbance of radiation. Carbon dioxide, which is emitted by the burning of fossil fuels, is a major greenhouse gas.
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