When sources describe global warming potential of different gasses, such as in this paper on radiative forcing, methane and tropospheric ozone respectively are given GWP values of around 29 and 65. However, when I look at spectra for the three gasses or diagrams showing outgoing blackbody radiation from the earth, it doesn't look like the radiative forcing effect for methane and tropospheric ozone should be that much higher than CO2. I've hunted around a bit, and have seen the same values for GWP of methane and ozone in many sources, but haven't been able to figure out why those gasses are so much more potent than CO2.

Why is the global warming potential of tropospheric ozone and methane so high?

  • $\begingroup$ In the outgoing longwave radiation plot methane isn't there, because there is not much of it in the atmosphere. The GWP is a quantity per unit mass or unit particle, so having way less CH4 than CO2 in total will only weaken its total impact. $\endgroup$ Jul 25, 2022 at 9:03
  • $\begingroup$ @AtmosphericPrisonEscape It's on the NASA GISS plot at around 1300 cm^-1, which makes sense, given that it's estimated as the second most impactful greenhouse gas, despite being present in only small quantities. What I'm wondering is why the impact is so high, given its limited presence. $\endgroup$
    – ckersch
    Jul 25, 2022 at 16:20
  • 1
    $\begingroup$ I repeat myself: The GWP is a quantity per unit mass. I.e. at same mass in the atmosphere of CO2 and CH4 they would have relative contributions to the greenhouse warming potential of 4 and 28. But they are not at equal mass in the atmosphere. CH4 is, so far, much less present. The rest of your question boils down to where the absorption bands are, which is the quantum physics of molecules. $\endgroup$ Jul 26, 2022 at 2:14


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