The math here is quite simple.

A single cow can produce around 250 to 500 liters of methane per day through belching and farting. Let's take an average of 400 liters/day. Methane is a potent greenhouse gas.

400 liters/day × 365 days = 146,000 liters/year.

Convert to kilograms (since methane’s density is ~0.656 kg/m³):

146,000 liters = 146 m³ → 146 × 0.656 kg = 95.8 kg of methane/year per cow.

Methane has a global warming potential (GWP) of about 28 times that of CO₂ over 100 years. So, 1 kg of methane is equivalent to 28 kg of CO₂ in terms of warming effect.

95.8 kg of methane × 28 = 2,682 kg of CO₂ equivalent per year per cow.

2,682 kg CO₂e/year × 1 billion cows = 2.68 billion metric tons of CO₂ equivalent annually.

Cool. Now compare cow farts to all other sources, that’s the only metric that matters.