[randolph]

This quote might give a better idea of the contribution of various gases to warming. As shown, the contributions of methane relative to co2 is highly variable. 50% methane contribution is to high based on this data, ranging from 34% to 44% compared to co2

From Wikipedia.
"The contribution to the greenhouse effect by a gas is affected by both the characteristics of the gas and its abundance. For example, on a molecule-for-molecule basis methane is about eight times stronger greenhouse gas than carbon dioxide[6], but it is present in much smaller concentrations so that its total contribution is smaller. When these gases are ranked by their contribution to the greenhouse effect, the most important are:[7]

* water vapor, which contributes 36-72%
* carbon dioxide, which contributes 9-26%
* methane, which contributes 4-9%
* ozone, which contributes 3-7%

It is not possible to state that a certain gas causes an exact percentage of the greenhouse effect. This is because some of the gases absorb and emit radiation at the same frequencies as others, so that the total greenhouse effect is not simply the sum of the influence of each gas. The higher ends of the ranges quoted are for each gas alone; the lower ends account for overlaps with the other gases.[8][7] The major non-gas contributor to the Earth's greenhouse effect, clouds, also absorb and emit infrared radiation and thus have an effect on radiative properties of the greenhouse gases."