3 ms·

>Methane, molecule per molecule, has an infrared-cross section about 20 times that of carbon dioxide. How do you square that with the IPCC estimate that methan

• MagnumOpus 4y ago
  Methane decomposes into CO2 over centuries. So CO2's atmospheric forcing is a constant over time, while methane forcing starts 100s of times worse but decays over time. Over 100 years the forcing is on average about 30x higher, over 20 years on average about 84x higher[1]. [1] https://unece.org/challenge https://unece.org/challenge
• mzs 4y ago
  so about 40% instead of 10%
• sampo 4y ago
  > How do you square that with the IPCC estimate that methane is 84 times more potent than CO2 over a 20-year period? Maybe: https://en.wikipedia.org/wiki/Global_warming_potential#Calculating_the_global_warming_potential https://en.wikipedia.org/wiki/Global_warming_potential#Calcu...
• photochemsyn 4y ago
  I think that's mostly the effect of methane oxidation in the stratosphere delivering water vapor to the stratosphere, plus reduction of the concentration of OH radical in the atmosphere, and some effects on stratospheric ozone: > "Methane enhances its own lifetime through changes in the OH concentration, it leads to changes in tropospheric ozone, enhances stratospheric water vapour levels, and produces CO2. The GWP given in Table 2.14 includes the first three of these effects. The lifetime effect is included by adopting a perturbation lifetime of 12 years." - IPCC Report (That report indicates the radiative factor is more like 26:1 for CH4:CO2)