Methane has an atmospheric lifetime of 12 ± 3 years. The 2007 IPCC report lists the GWP as 72 over a time scale of 20 years, 25 over 100 years and over 500 years.  A 2014 analysis, however, states that although methane's initial impact is about 100 times greater than that of CO 2 , because of the shorter atmospheric lifetime, after six or seven decades, the impact of the two gases is about equal, and from then on methane's relative role continues to decline.  The decrease in GWP at longer times is because methane is degraded to water and CO 2 through chemical reactions in the atmosphere.
Yours is the 1st website on my Google search for evidence to cite to people who don’t believe global warming is manmade. But I can’t use your site and will proceed to others instead. The organization that owns/runs the site is not listed nor are your funders. If you must be secret about these things, I guess you must. But I can’t use you without evidence that you are a legitimate, science-based group and are not funded by people who are partisan or who stand to somehow reap financial or political gain from activities that oppose fossil fuels. I look forward to your reply by email.
Carbon dioxide, methane, nitrous oxide and the fluorinated gases are all well-mixed gases in the atmosphere that do not react to changes in temperature and air pressure, so the levels of these gases are not affected by condensation. 4 Water vapor on the other hand, is a highly active component of the climate system that responds rapidly to changes in conditions by either condensing into rain or snow, or evaporating to return to the atmosphere. Thus the impact of the greenhouse effect is primarily circulated through water vapor, and it acts as a fast feedback. 4