The difference is, now, thanks to humans, there are 1.4 billion cows. And a lot of the cows are fed things like corn, which makes them produce a lot more methan

The difference is, now, thanks to humans, there are 1.4 billion cows. And a lot of the cows are fed things like corn, which makes them produce a lot more methane than a more natural diet would. A million years ago, you wouldn't have anywhere near this many ruminants.