Fig. 5
From: Revisiting enteric methane emissions from domestic ruminants and their δ13CCH4 source signature
Country average δ13CCH4-ruminant in 2000s, and the changes in δ13CCH4-ruminant between 1960s and 2000s (∆ (δ13CCH4-ruminant)). The ∆ (δ13CCH4-ruminant) is here calculated from the diet shift only (i.e., changes in the relative C3–C4 fraction in feeds) without accounting for decreasing δ13CCO2-atm incorporated in the biomass of grazed plants (see Methods). A positive ∆ (δ13CCH4-ruminant) indicates an increase of δ13CCH4-ruminant from 1960s to 2000s from a higher fraction of C4 in the diet
