The greenhouse effect — Earth science, 14–17 years
Certain gases slow the escape of infrared energy from Earth. The natural effect keeps the planet habitable, while extra greenhouse gases strengthen it and raise the average temperature.
A blanket for heat
Sunlight reaches Earth and warms land and oceans. They send energy back as invisible infrared radiation, but gases such as carbon dioxide, methane and water vapour absorb some of it and re-emit it in all directions. This slows cooling without making a solid roof around Earth.
Why this explanation matters
Earth’s temperature cannot be explained by sunlight alone: without an atmosphere that absorbs infrared radiation, the planet would be much colder. Scientists needed an energy-budget explanation for the observed temperature. Measuring gases and radiation shows why adding greenhouse gases changes the balance.
Following one energy packet
A patch of ground absorbs sunlight and warms. It emits infrared radiation upward; a carbon-dioxide molecule absorbs one wavelength and then re-emits infrared in random directions. Some energy goes upward, but some returns downward, so the surface must warm until outgoing energy again balances incoming energy.
It is not the same as a glass house
The name suggests that greenhouse gases warm Earth mainly by trapping air, as glass does in a garden greenhouse. That comparison is useful but incomplete. The key action is absorption and re-emission of infrared radiation; convection and air movement also matter in a real greenhouse.
From measurements to choices
The greenhouse effect is used in weather and climate models, satellite studies and planning for heat, water and crops. Burning coal, oil and gas adds carbon dioxide, while farming and waste can add methane. These sources can be compared with measurements to test how human activities alter the energy balance.
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