It doesn't matter if it has a strong effect at the molecular level if it exists in miniscule quantities 4 orders of magnitude less than water vapor while not trapping any part of the light spectrum that is not already captured by H2O and CO2. It has negligible, near zero effect at present. Sorry, if you factor the 20x factor for methane heat retention times .00017 it's the equivalent of increasing the amount of water vapor from 4% to 4.004% of the Earth's atmosphere. It is negligible no matter which way you look at it. If a .004% difference in humidity made a dramatic effect on heat retention you'd feel it.

Well, here's an analogy: If you have $1000 salary and $900 of fixed expenses (+ $100 of disposable income), then a reduction of just 10% in your salary reduces your disposable income by 100%. A reduction of 20% in your salary puts you deep into the red and will eventually make you homeless.

Climate is like your budget. There's a lot of factors flowing into it, and even a very small change (e.g. 0.1% additional water vapor) can flip the sign on the total balance. Sorry, but your argument about the magnitude of the problem is just wrong.

That's a bad analogy because the climate is not a single variable, number one. Two, your percentages are off by orders of magnitude with regards to Methane. Methane, as I said above, is 0.00017% of the earth's atmosphere. Even if it is 20 times more effective at retaining heat than Water Vapor (4% of earth's atmosphere), it's the equivalent of increasing your fixed expenses by .004%, or 4 cents by your $1000 example. 4 cents is negligible. No accountant would even bother listing it.