Although it's easy to label a gas as a GHG (green house gas) it may also be easy to forget just what this means and how it acts, this post highlight's what methane does to earn its label as a powerful GHG.
Okay so GHG as the name suggests means it behaves a little like the glass in a green house does - it is a layer that acts as a blanket, making it harder for energy to leave the body beneath yet still able to absorb incoming external radiation.
Methane absorbs radiation most effectively in 2 frequency bands seen below. Although the first absorption band is in a quiet part of the spectrum which doesn't see large amounts of incoming or outgoing radiation the second band is in a significant part of the outgoing, infrared spectrum very close to the peak emission wavelength of 10µm.
Okay so GHG as the name suggests means it behaves a little like the glass in a green house does - it is a layer that acts as a blanket, making it harder for energy to leave the body beneath yet still able to absorb incoming external radiation.
Methane absorbs radiation most effectively in 2 frequency bands seen below. Although the first absorption band is in a quiet part of the spectrum which doesn't see large amounts of incoming or outgoing radiation the second band is in a significant part of the outgoing, infrared spectrum very close to the peak emission wavelength of 10µm.
Figure 1
(adapted from Virginia, 2012)
So to clarify what does this mean exactly? It means methane is very good at absorbing radiation the earth has emitted. This energy is then trapped in the atmosphere, rather than being emitted to space and hence warming the earth.
This really though is only half the story, visit back soon to find out more about the lesser known secondary warming effects of this interesting GHG.
Hi Rob, interesting post about the absorption of radiation coming off the Earth, but what affect does methane have on radiation coming into the Earth (ie from the Sun)?
ReplyDeleteFurthermore, is it ok if i mention your blog in mine? As of yet I haven't dug into what green house gases are warming up the atmosphere, it would be a great if I could direct people here who might be interested in it.
ReplyDeleteHi Olllie, thanks for that. Always something to consider of course yes - absorption occurs with incoming solar radiation as well as reflected radiation from the surface of the earth. By all means please feel free to link content to this post if it fits well with your blog. Best, Rob
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