Can somebody please explain this statement (about the greenhouse effect)? "Methane is a potent gas and over a period of 20 years has a 72 times greater effect on warming the atmosphere than carbon dioxide.
Due to my limited english, i am failing to understand how timeline has anything to do with the effect of a gas on the greenhouse effect. I think it has to do with the half life of the gas in the atmoshpere. Maybe methane is broken down more readily than CO2 and the whole thing means that if they remained in the atmosphere for the same amount of time, methane will do a greater damage. Am i right ?
"Methane has a large effect (24 times as strong as carbon dioxide per unit mole) for a brief period (having an estimated lifetime of 8.9±0.6 years in the atmosphere),[12] whereas carbon dioxide has a small effect for a long period (over 100 years). Because of this difference in effect and time period, the global warming potential of methane over a 20-year time period is 72."[ Wikipedia, quoting Jain, Briegleb et al ].

Simplified, that means:


$\ce{CH4}$ has a shorter half-life in the atmosphere than $\ce{CO2}$, reducing its effect as a green-house gas over time, but
$\ce{CH4}$ is so much more potent in retaining heat than $\ce{CO2}$ that this more than compensates for its short lifetime, making $\ce{CH4}$ a stronger green-house gas over the long term.