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. This study quantifies China’s millennial land carbon dynamics (851–2022). Historical emissions from deforestation were fully offset by 1980–2022 sinks, driven by CO2 fertilization and afforestation, highlighting regional impacts on global carbon balance.