Cow methane is just the natural carbon cycle, it's not adding anything, right?
Short answer: Partly true: biogenic methane is recycled carbon, unlike fossil emissions. But a large, stable herd still keeps a heavy warming load aloft, and the climate pays for it.
Methane breaks down in roughly a decade, but while it's up there it traps heat far harder than CO₂, and a steady herd keeps refilling the stock.
Carbon Brief; UC Davis CLEAR Center; Garnett et al. (2017)
The objection
“Cow methane is just recycled carbon, the grass pulls CO₂ down, the cow breathes it back out. It’s a closed loop, not pollution like fossil fuels.”
The answer
This is the most sophisticated version of the natural-cycle argument, and the chemistry behind it is genuinely correct. Biogenic methane is recycled carbon: plants pull CO₂ from the air, the cow converts some to methane, and after roughly twelve years it oxidises back to CO₂ [1]. That really is different from fossil methane, which injects carbon that was locked away for millions of years. A critic who makes this distinction has earned a fair hearing.
But two things gut the “adding nothing” conclusion. The first is that methane is a ferocious warmer while it’s up there, roughly 80 times the heat-trapping power of CO₂ over 20 years [2]. A large herd does more than recycle carbon. It maintains a permanently topped-up reservoir of a potent gas. Stop refilling it and warming eases; keep the herd steady and you hold that heating load in place indefinitely.
The second is that the metric powering this argument, GWP*, cuts both ways. A shrinking herd does cause little additional warming. But the same logic means today’s large herds already locked in warming when they were built up, and merely holding them flat doesn’t undo it [2]. Ruminants produce roughly a third of all human-caused methane [3]. That is a standing contribution, not a neutral loop.
So grant the biology. It’s recycled carbon rather than fossil. It is still a vast, ongoing heat load we choose to maintain, and the fastest climate lever we have is to stop maintaining it.