O emissions were present in pre-industrial times, only the difference between current and pre-industrial emissions represents net human-induced climate change. Meanwhile, large uncertainty exists in previous estimates of pre-industrial N2
O emissions from the land biosphere. Our estimate using process-based model was the first study that provided the pre-industrial N2
O emission at biome-, sector- or country-, and global-level, which could be a useful reference for future climate mitigation.