I used to link to the EPA but I learned this week that they might be a captured agency(1). They used to have a website section devoted to methane, it’s sources, and it’s contribution but it’s either been taken down or I simply can’t find it.

However, Bill Gates writes in his blog that Agriculture contributes towards 24% of the world’s climate change and that “Cattle are a huge source of methane; in fact, if they were a country, they would be the third-largest emitter of greenhouse gases!”(2). His blog post that I link to below is admittedly a secondary source but I think he does a pretty good job at showing the big picture.

Sources:

(1)https://en.m.wikipedia.org/wiki/Regulatory_capture

(2)https://www.gatesnotes.com/Energy/My-plan-for-fighting-clima...

If you go on to find a good (hopefully primary) source, please reply with it here!