It's not a stronger greenhouse gas than CO2 when it's sitting in a tank, and it's not a stronger greenhouse gas when it's emitted as hot, reactive exhaust into the atmosphere, where it is immediately reduced to CO2, CO, H2, H, H2O, HO, and so on.

But, like I said, premature and superfluous, even though we should still do our accounting carefully, and not rely on "OMG methane!" as the guiding principle of our thinking.