On a per-molecule basis, methane is 26 times more effective as an infrared absorber than is CO2. Calculate the corresponding ratio on a per-unit basis, and compare it to the 20-year GWP for methane which has an atmospheric lifetime of 11 years, a global warming potential (relative to CO2) of 67 in 20 years, 23 in 100 years, and 6.9 in 500 years. What's the reason for any discrepancy you find?

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