Methane is a short-lived potent greenhouse gas. In regards to the effect on global warming there is no cushy cute 'circle of life its all natural dude ' effect, methane release heats the world.

Even ignoring methane gas releases the production of red meat causes higher emissions of co2 than comparable plant-based proteins. These emissions originate from feed crop production, synthetic and organic fertilizer application, manure storage, land-use changes like deforestation for pastures, on-farm energy use, and meat processing and transport. As you see most of these are 'running costs', and reducing global meat consumption would reduce emissions.