Intensification of farming since the Green Revolution has led to large increases in yield but has also increased anthropogenic greenhouse gas emissions. Here, by providing a global comprehensive cradle-to-gate quantification from seed to yield, we show that the global warming potential (GWP) of conventional agriculture of grain crops has increased eightfold from 1961 to 2020, whereas the sustainability index (SI) has decreased threefold. Tillage, synthetic fertilizers and irrigation together accounted for 90% of the increased GWP, linked to tenfold increases in fertilization and groundwater use and more than doubled mechanized and irrigated areas. We highlight regions with high GWP and low SI, such as South Asia, and project further threefold increases in agriculture GWP by 2100 compared with 2020 (3.3 ± 0.73 PgCO2e) driven by declined use efficiency of the inputs. Green energy and climate-smart agriculture techniques can reduce the projected GWP in 2100 to 2.3 PgCO2e and increase the SI fourfold.