I understand that visible light can (largely) go through greenhouse gases, but infrared radiation can get reflected back... why can visible light go through green-house gases?

Does it have to do with shorter wave-length of the visible light? i.e. are green house gases like a sieve that only allow shorter wavelengths in?

  • $\begingroup$ Do you understand how the quantized energy levels of atoms allow only the absorption of photons whose energies are equal to the differences in energy levels? $\endgroup$
    – G. Smith
    Nov 30, 2019 at 5:44
  • $\begingroup$ The IR radiation isn't reflected. It is absorbed then re-emitted in a random direction i.e. 50% of the re-emitted radiation on average ends up headed back downwards. $\endgroup$ Nov 30, 2019 at 6:13
  • $\begingroup$ @JohnRennie: thanks for your comment. So Co2 (or any other GH gas) absorbs infrared light, and then re-emits the infrared light in a random direction? Are you able to give a little more info about this please? Does Co2 enters an "unstable state" after absorbing the infrared light and that's why it re-emits it again? $\endgroup$ Nov 30, 2019 at 6:20
  • $\begingroup$ @HoomanBahreini $\textrm{CO}_2$ has vibrational transitions at IR wavelengths so an IR photon is absorbed and excites the molecule to a higher energy state. The molecule then spontaneously decays back to the ground state and re-emits the photon in a random direction. $\endgroup$ Nov 30, 2019 at 6:36
  • $\begingroup$ @JohnRennie: thanks a lot... So does it mean that visible light has too much energy? I assume excite means that an electron absorbs energy and jumps to higher level? So an infrared light has just the right amount of energy for this to happen, whereas visible light has too much energy so it cannot be absorbed? $\endgroup$ Nov 30, 2019 at 6:43


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