I am going to assume that you meant CH4, not CO2. For the major contributor of CO2 is the burning of fossil fuels. And the leveling off of the CH4 was created by the switch to dryland rice farming, not a decrease in ruminents. The sudden present increase is due to the outgassing of the permafrost areas, and Arctic Ocean clathrates. Those are major feedbacks created by the warming that CO2 has caused.
As for the rest of your sillyness, the CH4 levels were not increasing when we had vast herds of buffulo, wildebeast, and caribou. They began increasing when the wetland rice farming increased as Asia's population ballooned.
If it is solely due to permafrost heating, then why the rise in methane levels in the southern hemisphere? See...
Global-warming methane spiked in 2007 - environment - 30 October 2008 - New Scientist
They say a rise in methane in the northern hemisphere
might be the result of a year-long warm spell in Siberia, where wetlands harbour methane-producing bacteria,
but they have no immediate answer as to why emissions rose in the southern hemisphere at the same time.
You seem to state that long term warming in Siberia is matter of factly the cause. Whereas scientists and researchers state it might be the cause of elevated methane levels. Also you offer no reason at all, of the elevated methane levels in the southern hemisphere.
As far as meat production not being the major contributor to CO2 emmissions...
UNÂ’s Top Climate Scientist Urges People to Combat Climate Change by Eating Less Meat : Planetsave
CIWFÂ’s ambassador Joyce DÂ’Silva told the BBC:
“Surveys show people are anxious about their personal carbon footprints and cutting back on car journeys and so on; but they may not realize that changing what’s on their plate could have an even bigger effect.”
BBC NEWS | Science/Nature | Shun meat, says UN climate chief
UN figures suggest that meat production puts more greenhouse gases into the atmosphere than transport.