The term greenhouse effect comes from an analogy to greenhouses. The Earth's surface temperatures are much lower, so it emits longwave thermal infrared radiation (radiated heat).

The Sun is about 5,500 ☌ (9,930 ☏), so it emits most of its energy as shortwave radiation in near infrared and visible wavelengths (as sunlight). The wavelengths differ because matter radiates energy at a wavelength related to its temperature. Greenhouse gases work by being transparent to wavelengths of radiation emitted by a star like the sun, but absorbing wavelengths of radiation emitted by planets like the Earth. As a result, global warming of about 1.2 ☌ (2.2 ☏) has occurred since the industrial revolution, accelerating to a rate of 0.18 ☌ (0.32 ☏) per decade more recently. In addition to naturally present greenhouse gases,īurning of fossil fuels has increased amounts of carbon dioxide and methane in the atmosphere. The Earth's average surface temperature would be about −18 ☌ (−0.4 ☏) without the greenhouse effect, compared to Earth's 20th century average of about 14 ☌ (57 ☏), or a more recent average of about 15 ☌ (59 ☏). Adding greenhouse gases to the atmosphere increases the warming effect. This reduction in planetary cooling raises the planet's average surface temperature. Greenhouse gases absorb some of that radiation, reducing the amount of energy that escapes into space. The warm surface of a planet emits infrared thermal radiation. A planet is warmed by absorbing light from its host star and cooled by radiating energy into space. The greenhouse effect occurs when greenhouse gases in a planet's atmosphere trap some of the heat radiated from the planet's surface. Quantitative analysis: Energy flows between space, the atmosphere, and Earth's surface, with greenhouse gases in the atmosphere absorbing and emitting radiant heat, affecting Earth's energy balance.

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