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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