It's important to remember that by and large, these figures are compiled based upon a proverbial HOST of projections, probabilities, and circular logic. From a climatology standpoint, there are many things that produce Methane Gas, and while our actions can largely be made to blame; our population is the biggest issue.
Freshwater/Wetlands/Ocean Water and interestingly termites make up ~32% of methane emission. What's not taken into account is our effect on the output of methane FROM Freshwater/Wetlands/Ocean Water/Termites/Release of fossil fuels, etc.
So, that being said 'latest data' would actually be an attempt to extrapolate how much of an effect we've had on the natural elements, and how much we've actually changed the earth as a whole. Once that can be established, and established on a per-capita plane; we'll be capable of determining our output and damage over-time.
It's not killing us, in fact - it will eventually escape quite successfully. Though, how it escapes the earth is another story altogether...which, I suppose is the real killer.
