The problem with methane estimates is that they’re just that: estimates. No one from the EPA is standing out in a pasture measuring how much gas comes out of each individual cow. Our estimates are based on data, but scientists have to make certain assumptions in scaling that data up to account for every bovine. And it’s not just “how much methane does the average cow emit in a day?” It’s also how big the average dairy cow is, how much each animal eats, how much dairy and feed cattle differ in size, how their manure is handled, and so on. There aren’t universal guidelines for these things, so climatologists have to build models. When those models are based on outdated information, they’re bound to be inaccurate.