The greenhouse gases absorb infrared radiation emitted from objects warmer than absolute zero. On a molecular level a lot of different processes are taking place, that causes the greenhouse effect to take place:

  • The infrared radiation from the sun, strikes a molecule such as carbon dioxide and causes the bonds to bend and vibrate.
  • The infrared radiation is absorbed by the molecules and photons of energy causes the molecules to gain kinetic energy.
  • This extra kinetic energy may then be transmitted to other molecules such as oxygen and nitrogen through random collisions.
  • This causes other molecules to gain in kinetic energy and then they start to vibrate faster at their natural frequency (resonance) in the infrared region.
  • These resonating molecules results in a general heating of the atmosphere, as average kinetic energy (temperature) is higher than before due to absorbtion.
  • One way to think of it is if you have a slinky and you stretch it a little. Then vibrate only one end of the slinky, the rest of the slinky will also start to resonate. The reason is because the energy of the bump is absorbed by the vibrations in the slinky and the extra energy is transferred into the rest of the slinky causing it to vibrate also.

Vibrating molecules
Vibrating molecules

This animated diagram illustrates the different ways in which carbon dioxide molecules vibrate and rotate when they absorb energy. This process heats up the atmosphere.