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.