The Greenhouse Effect

Greenhouse gases keep the Earth’s temperature warm enough to support living organisms. Without them, the planet would be too cold for most organisms to survive. The three main greenhouse gases in the atmosphere are:

  • Water vapour
  • Carbon dioxide
  • Methane

The amount of water vapour in the atmosphere changes depending on the temperature. Below you can see a diagram of the Earth and the atmosphere.

Water vapour is particularly significant because its amount in the atmosphere can change depending on temperature. This change can then affect the amount of energy trapped in the atmosphere.

Diagram illustrating the greenhouse effect: Sunlight reaches the Earth's surface, reflecting back as heat. Some heat is trapped by the atmosphere, while some escapes. Greenhouse gases including methane, carbon dioxide, nitrous oxide, CFCs and haloalkanes are shown contributing to the trapping of heat.

Let’s look at how the greenhouse effect works.

1. The Sun emits energy as shortwave radiation, such as ultraviolet (UV) rays and visible light.

2. Most of the shortwave radiation easily passes through the Earth’s atmosphere and reaches the surface. However, some of it is reflected back into space.

3. The Earth’s surface absorbs most of the solar energy, and then re-emits it as longwave radiation, such as infrared.

4. Greenhouse gases in the atmosphere absorb some of this longwave radiation.

5. By absorbing this energy, greenhouse gases increase the temperature of the atmosphere. This increase in temperature is known as the greenhouse effect.

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