Livestock, Methane and Climate
D. Alexander, J. D. Ferguson, A. Glatzle, W. Happer, W. A. van Wijngaarden
TL;DR
This paper assesses whether methane emissions from livestock meaningfully affect Earth's climate. It uses a simple methane-balance model with linear population trajectories for cattle ($B(t)=a_B+b_B t$) and sheep ($O(t)=a_O+b_O t$) and a fixed methane lifetime ($\tau$) to compute atmospheric CH$_4$ perturbations and radiative-forcing effects. The key result is that 2025 cattle- and sheep-derived CH$_4$ contributions amount to roughly 357 ppb and 38 ppb, driving temperature changes of approximately $-0.04^{\circ}$C and $-0.004^{\circ}$C respectively; even the New Zealand 14–24% pledge would yield at most $-5$ to $-8 \times 10^{-6}$ °C, far below detectability. Consequently, policies targeting livestock methane offer negligible climate impact under plausible land-use feedbacks, though they may be pursued for other reasons.
Abstract
Methane emissions by livestock have a negligible effect on Earth's temperature. For example, killing all of the approximately 1.6 billion cattle on Earth in the year 2025, when this paper was written, would only reduce atmospheric methane concentrations enough to change the temperature by -0.04 C. Killing all 1.3 billion sheep would lead to a temperature change of -0.004 C. New Zealand's pledge to reduce methane emissions of their livestock by 14% to 24% from those in the year 2017 would change the temperature by -0.000005 to -0.000008 C, far too small to measure. These are maximum temperature savings where methane emissions from domestic livestock are not replaced by other sources (such as wild ruminants and termites) during the inevitable rewilding of managed grasslands and rangelands.