Adding carbon dioxide (CO2), and methane (CH4) to the atmosphere are two completely different things. CO2 can be re-captured by plants and photosynthesized to s

Adding carbon dioxide (CO2), and methane (CH4) to the atmosphere are two completely different things. CO2 can be re-captured by plants and photosynthesized to separate carbon + oxygen. So as you pointed out, planting a tree and burning a tree cancel each other out in theory (if you burn the tree 100% cleanly). CH4 breaks down into other stuff, but it doesn't go back into plants. To answer your last question, methane is transient (~10 years or so). But as long as the cows are around, that really doesn't matter.