The greenhouse effect warms planets — Science, 14–17 years
Certain gases absorb and re-emit infrared radiation, slowing the escape of heat to space. The natural effect makes Earth habitable; increasing it changes the planet’s energy balance.
How the greenhouse effect works
Sunlight brings energy to Earth, and the warm surface sends some of it back as infrared radiation. Greenhouse gases absorb parts of this radiation and emit it again in all directions, including back towards the surface.
The problem it explains
Without the natural greenhouse effect, Earth would lose heat much faster and its average surface would be far colder. Scientists developed the explanation to account for why a planet’s temperature is not determined by sunlight alone.
Worked example: comparing planets
Venus receives sunlight, but its thick carbon-dioxide atmosphere traps much infrared radiation. Its surface is about 465 °C, far hotter than Mercury’s average surface, even though Mercury is closer to the Sun. Atmosphere matters.
The heat-trap mistake
It is reasonable to picture greenhouse gases as a lid that stops all heat escaping. In reality, heat still leaves for space; the gases slow its escape by absorbing and re-emitting infrared radiation. The balance shifts until outgoing energy matches incoming energy.
Where it is used
Climate scientists use greenhouse-effect physics in models that test how changes in gases, clouds, ice and oceans affect temperature. The same idea helps explain measurements from satellites and temperature differences between planets.
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