Revisiting enteric methane emissions from domestic ruminants and their \u03b413CCH4 source signature

Jinfeng Chang,Shushi Peng,Hanqin Tian,Philippe Bousquet,Marielle Saunois,Mario Herrero,Shree R S Dangal,Petr Havlík,Philippe Ciais

doi:10.1038/s41467-019-11066-3

Abstract

Accurate knowledge of 13C isotopic signature (δ13C) of methane from each source is crucial for separating biogenic, fossil fuel and pyrogenic emissions in bottom-up and top-down methane budget. Livestock production is the largest anthropogenic source in the global methane budget, mostly from enteric fermentation of domestic ruminants. However, the global average, geographical distribution and temporal variations of the δ13C of enteric emissions are not well understood yet. Here, we provide a new estimation of C3-C4 diet composition of domestic ruminants (cattle, buffaloes, goats and sheep), a revised estimation of yearly enteric CH4 emissions, and a new estimation for the evolution of its δ13C during the period 1961–2012. Compared to previous estimates, our results suggest a larger contribution of ruminants’ enteric emissions to the increasing trend in global methane emissions between 2000 and 2012, and also a larger contribution to the observed decrease in the δ13C of atmospheric methane.

Highlights

Accurate knowledge of 13C isotopic signature (δ13C) of methane from each source is crucial for separating biogenic, fossil fuel and pyrogenic emissions in bottom-up and top-down methane budget
Large uncertainties exist in both approaches, which limits the complete understanding of the global methane budget
The increasing share of concentrate feeds for poultry and pigs could be due to the larger increase in the production of poultry and pigs compared with that of ruminant, and the δ13CCH4-atm δ13CCH4-sources δ13CCH4-ruminant δ13Cdiet DM ECH4 EGE FCH4-ruminant feed conversion ratios (FCR)

Summary

Introduction

Accurate knowledge of 13C isotopic signature (δ13C) of methane from each source is crucial for separating biogenic, fossil fuel and pyrogenic emissions in bottom-up and top-down methane budget. Livestock production is the largest anthropogenic source in the global methane budget, mostly from enteric fermentation of domestic ruminants. Understanding the global methane budget and its sources is crucial for climate mitigation efforts Both process-based (bottom-up) and atmospheric-based (top-down) methods are used to constrain the sources and sinks of methane. The measurements of the 13C stable isotope composition of atmospheric methane (i.e., δ13CCH4-atm) bring additional constraints for attributing methane emission sources[3,4,5,6]. Biases in the mean isotopic signatures of individual sources and how they change with time translate into potentially large uncertainties on the inferred trends of emission in this approach[8]. Given the large magnitude of ruminant emissions (FCH4-ruminant), its δ13C (δ13CCH4-ruminant) needs to be assessed as precisely as possible regionally for constraining the global mix of emissions using inversion models driven by atmospheric CH4 and isotope data

Methods

Results

Conclusion