As long as the carbon contained in that methane comes from environmental carbon, rather than fossil carbon, the net effect on CO2 levels is 0. If a tree absorb

As long as the carbon contained in that methane comes from environmental carbon, rather than fossil carbon, the net effect on CO2 levels is 0. If a tree absorbs CO2 to grow, dies, gives off methane and that methane eventually turns back into CO2, it's not a problem. That's just the natural carbon cycle. The problem is that we're constantly injecting more carbon from deep underground into that carbon cycle. It's why biofuels are essentially carbon neutral.