Diverging Agricultural Greenhouse Gas Emissions and Partial Convergence of Source Structures Across the EU-27 and Mercosur-4

This study examines agricultural greenhouse-gas (GHG) emission scale and source composition across a fixed EU-27 geographical cohort and Mercosur-4 (Argentina, Brazil, Paraguay, and Uruguay) over 2002–2023. Using FAOSTAT emissions totals, a balanced nine-source profile is constructed for 31 countries (682 country-year observations). Hellinger and Aitchison distances, Kendall–Theil–Sen trends, Ward.D2 clustering, PERMANOVA/PERMDISP, , and sensitivity analyses distinguish aggregate emission-weighted profiles from equal-country profiles. Common9 emissions declined by 10.0% in the EU-27 but increased by 26.1% in Mercosur-4. The emission-weighted inter-bloc Hellinger distance showed no statistically supported trend (tau = −0.177, p = 0.248), whereas the equal-country distance declined by 4.5% (tau = −0.688, p < 0.001). CoDA6 Aitchison distance declined by 5.2% (tau = −0.610, p < 0.001), but this result concerns a distinct six-part strictly positive subcomposition rather than confirming Primary9 convergence. EU within-bloc dispersion increased by 6.4%. Two recent Primary9 EU regimes are identified, but their partition is sensitive to drained organic soils. The study therefore finds scale divergence and estimand-specific partial compositional convergence, providing a pre-application, non-causal baseline for post-2026 monitoring. Conditional inclusion of rice under a stated zero-fill assumption preserves the contrasting weighted and equal-country trends; absolute-share-gap diagnostics qualify the geometry-dependent contribution of drained organic soils.