Millennial land carbon emissions in China offset by carbon sinks of the past four decades

China experienced substantial millennial-scale climate and anthropogenic land use changes, yet their combined impacts on land carbon dynamics remain largely unexamined. Here, we quantify spatiotemporal changes in terrestrial organic carbon over 851-2022 using a land surface model driven by reconstructed climate and land cover forcings. Simulated results show China's pre-industrial millennial land carbon dynamics aligned with global carbon stock and atmospheric CO₂ fluctuations, such as the ~284 ppm peak in the 12th century linked to land use during the Medieval Climate Anomaly-warmed Song Dynasty. Notably, China's total land carbon emissions (13 ± 0.5 PgC) accounted for 22% of global land carbon emissions during 1700-1900, with Northeast and Southwest China experiencing the largest historical land carbon losses from intensive deforestation. Nevertheless, the 17.0 ± 1.7 PgC emissions during 851-1980 were fully offset by rapid carbon sinks over 1980-2022, driven by CO₂ fertilization and large-scale afforestation. These findings provide insights into China's historical land carbon dynamics, their underlying drivers, and global implications.