Radiation & Temperature Change (Edexcel GCSE Physics)

Temperature of the Earth

Higher Tier Only

• If the Earth had no atmosphere, the temperature on the surface would drop to about −180 °C at night, the same as the Moon’s surface at night

  • This would happen because the surface would be emitting all the radiation from the Sun into space

• The temperature of the Earth is affected by factors controlling the balance between incoming radiation and radiation emitted

• The Earth receives the majority of its heat in the form of thermal radiation from the Sun

  • At the same time, the Earth emits its own thermal radiation, with a slightly longer wavelength than the thermal radiation it receives (the surface temperature of the Earth is significantly smaller than the surface temperature of the Sun)

• Some gases in the atmosphere, such as water vapour, methane, and carbon dioxide (greenhouse gases) absorb and reflect back longer-wavelength infrared radiation from the Earth and prevent it from escaping into space

  • These gases absorb the radiation and then emit it back to the surface

• This process makes the Earth warmer than it would be if these gases were not in its atmosphere

The Earth receives thermal radiation from the Sun but emits its own thermal radiation at the same time

• The temperature of the Earth, therefore, depends on several factors, such as the rate that light and infrared radiation from the Sun are:

  • Reflected back into space

  • Absorbed by the Earth’s atmosphere or by the Earth’s surface

  • Emitted from the Earth’s surface and from the Earth’s atmosphere into space

The Greenhouse Effect

• The rate of absorption and emission of radiation on Earth contributes to the Greenhouse Effect

  • This is the natural process that warms the Earth's surface from the Sun

• The Sun's thermal radiation reaches the Earth's atmosphere where:

  • Some radiation is reflected back to space

  • Any radiation not reflected is absorbed and re-radiated by greenhouse gases

• The absorbed radiation then warms the atmosphere and the surface of the Earth

  • This is similar to what happens in a greenhouse to keep a humid, and warm temperature to grow plants