Agricultural Greenhouse Gas Emissions in Portugal: Long-Term Trends, Mitigation Pathways, and Carbon Removal

Agriculture is both a source of greenhouse gases (GHGs) and a potential carbon sink, so mitigation must distinguish direct emission reduction from carbon removal. This study quantifies Portuguese agricultural emissions and assesses how carbon farming and biochar can complement source-specific mitigation. FAOSTAT data for 11 farm-gate sources (1990–2023) are analysed alongside, but not merged with, harmonised EEA/Eurostat CRF 3 data for Portugal and the EU-26 (2005–2023). Long-run patterns are assessed using the Hamed–Rao modified Mann–Kendall test, Sen slopes and exploratory Pettitt diagnostics. Farm-gate emissions declined by 14.36%, and the adjusted test supported a decreasing aggregate trend (τ = −0.426, p = 0.0227, q = 0.0458; Sen slope = −37.19 kt CO2e yr−1). Manure management and synthetic fertilisers also declined significantly; enteric fermentation was not significant after serial-correlation correction, and on-farm energy showed no monotonic trend. Under CRF 3, Portuguese emissions increased by 0.81% from 2005 to 2023, whereas the EU-26 declined by 6.97%. Direct CH4, N2O and energy-related mitigation should be prioritised, with carbon farming and biochar carbon removal used as complementary options subject to additionality, permanence, life-cycle accounting and robust MRV.