Note that methane only blocks the infrared radiation that water vapor already almost completely blocks.
Note the 4.3um and 14.9um CO2 absorption bands. However, the amount of possibly planet warming 4,3um infrared radiation is fundamentally insignificant. The 14.9um CO2 absorption band can only have a very, very modest future additional effect (at its shorter end).
Fundamental science tells us that we have no need to fear either burping cows or CO2-emitting motor vehicles.