• Question: If the infa red rays cannot escape, increasing greenhouse gases, how come they can penetrate the greenhouse gas layer?

    Asked by babybel to Andrew, Emma, Marianne on 14 Jun 2010 in Categories: .
    • Photo: Andrew Maynard

      Andrew Maynard answered on 12 Jun 2010:

      Hi babybel,

      Good question. The answer is that they are not infrared rays when they arrive at the earth initially, but they are re-radiated as infrared radiation.

      Radiation hitting the Earth from the Sun covers a huge range of wavelengths, including everything from gamma rays and X-rays to visible light, and out to radio waves. Some of these wavelengths penetrate to the surface of the earth more easily than others, and some of them are absorbed by the Earth’s atmosphere and surface, where they heat things up.

      And this is the clever bit. When something gets hot, it emits infrared radiation – and this is the radiation that gets partially trapped in the Earth’s atmosphere. Effectively, the process of heating up and re-radiating the Suns rays transforms the radiation from the Sun from something that can easily get through the atmosphere, to something that struggles to get through – the result being that the Earth can’t get rid of the energy being absorbed from the Sun as fast as it arrives, so it heats up.

    • Photo: anon

      anon answered on 14 Jun 2010:

      I think that yet again AndrewM has scooped us all with a neat and simple answer aided and abetted by fluffybunny. I’m not going to compete. I wonder whether you’ve heard any of the wackier solutions to global warming? Geoengineering anyone?

      I’m not an expert in this field but I believe there are folk who propose shooting sulpuhr dioxide (SO2) into the atmosphere in order to block solar radiation and reduce global warming. This is supposed to mirror the effect of a massive volcanic eruption. It doesn’t do anything about ocean acidification however….!

      Any other wacky solutions to the problem? Any new ideas?

    • Photo: anon

      anon answered on 14 Jun 2010:

      Hi Babybel – good question! The incoming radiation form the Sun is mostly in the form of visible light and largely in the wavelength range of 0.2-4um. About 50% of the sun’s energy is absorbed at the earth’s surface and the rest is reflected. The wavelength that is reflected is in the wavelength range of 4-100um and is called infra-red rays. At these wavelengths, greenhouse gases that were largely transparent to incoming radiation from the Sun are more absorbant to infra-red. Some of the heat is radiated upwards and some downwards. Changes in the amount of certain gases affects how much heat is radiated upwards and downwards and this imbalance has led to what we now call “global warming”. I hope this answers your question!:).

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