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Over 100 years, Methane has a Global warming potential 34 times bigger than Carbon dioxide. Over 20 years, it's even 86 times bigger. How does one arrive at these numbers?

Looking at the following graphic doesn't help either, as the area for Methane barely covers the left margin of the upgoing thermal radiation and Carbon dioxide is at the right margin. The area under the absorption curve for Carbon dioxide is definitely bigger than the one for Methane.

Atmospheric Transmission

Source: https://commons.wikimedia.org/wiki/File:Atmospheric_Transmission.png

So what makes Methane a more effective greenhouse gas?

integralette
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  • By the way, why isn't there a tag environmental physics? – integralette Dec 27 '19 at 02:17
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    Does this answer your question? Why is methane considered an important greenhouse gas? – DavidH Dec 27 '19 at 02:27
  • maybe the users of https://earthscience.stackexchange.com/ or the https://chemistry.stackexchange.com/ would give better answers. – anna v Dec 27 '19 at 04:47
  • @integralette it is named "earth science" and is a different site https://earthscience.stackexchange.com/ – anna v Dec 27 '19 at 04:51
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    It is all described on the Wikipedia article that the OP links to himself. – my2cts Dec 27 '19 at 09:06
  • In particular, see the self-answer to the nominated duplicate question. – PM 2Ring Dec 27 '19 at 16:59
  • @my2cts: It is very hard to deduce the answer to this question from the wiki page, if it can be done at all. It requires understanding and calculating GWP values, and understand how the absorption bands relate to that. If you can do that, please add an answer to the given duplicate, as that question has no satisfactory answer either. – Lii Mar 20 '23 at 18:03
  • @DavidH: That question seem to be and exact duplicate. Unfortunately it doesn't have any good answers. The highest voted attempt at an answer consists of a bunch of speculation and the author concludes with "Well, I'm out of guesses". – Lii Mar 20 '23 at 18:05

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Global warming potential is given per mole, but you plot the atmospheric column-integrated effect.
Methane concentrations are about 2 ppm in the atmosphere, that of $\rm CO_2$ is 400 ppm, still methane manages to make a visible blip in the total atmospheric absorption plot.

As to any molecules "why is X a GHG, but Y is not?", the answer is in short "the positions and strength of the molecular absorption bands relative to the terrestrial infrared emission gives your greenhouse warming potential per mole", or in more words here on earth-science.

AtmosphericPrisonEscape
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