So the cow farts are a bit less than 8%. That isn't insignificant.
Two people have provided rough calculations that show they do have a measurable effect.
What's your point?
Me? I think we can probably survive some cow farts as our ancestors who hunted buffalo and burnt down entire ecosystems doing so did. We should focus on the real solutions that will move the needle, like proper human-scale city design and nuclear power.
Maybe there are other ways we could reduce their methane emissions short of getting rid of all of them.
I agree that other solutions are needed to properly address climate change though.
There is no silver bullet that's going to be a 25% reduction all on its own. The only way to win is a combination of changes each of which reduce emissions by a few percentage points.
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.