Harmonizing and Comparing Divergent Estimates of China’s Forest Carbon Sinks

• A new framework is established for collective analysis of NetFCflux across methods. • The carbon sink of Chinese forests varies greatly for different methods. • Improved comparability of NetFCflux through harmonization across methods. Various observational approaches, tools, and models have been developed to estimate forest carbon sinks to meet the global challenges of climate change under the Paris Agreement; however, significant differences persist in estimating China’s forest carbon sinks obtained using different methods. Here, remote sensing data were used to delineate managed and unmanaged forests in China, estimating the area of managed forests in 2018 at approximately 264 Mha, which closely aligns with the 272 Mha reported in the National Greenhouse Gas Inventories (NGHGIs). Of this total forest area, remote sensing data indicated that planted forests comprised 97 %. Then, land carbon sinks were derived from methods including NGHGIs, dynamic global vegetation models (DGVMs), atmospheric inversions (ATMs), and the Eddy covariance method (EC), using managed and unmanaged forest extent. The results reveal that significant gaps in forest carbon sink estimates persist across these methods, with a value of 240 TgC yr −1 for the inventory method, 115 ± 56 TgC yr −1 for DGVMs, 151 ± 68 TgC yr −1 for ATMs, and 627 ± 114 TgC yr −1 for EC during the period 2010–2018. These gaps are hypothesized to stem from inconsistencies in the definition of forest carbon sinks estimated using different methods. To address this, a consistent definition of NetFCflux was established, encompassing all carbon fluxes in and out of forest ecosystems. Relevant data were then used to bridge the gaps between various methods. Finally, the gaps in NetFCflux for Chinese forests between 2010 and 2018 narrowed significantly across the different methods, with a value of 240 TgC yr −1 for the inventory method, 181 ± 56 TgC yr −1 for DGVMs, 135 ± 68 TgC yr −1 for ATMs, and 353 ± 114 TgC yr −1 for EC. This collective analysis highlights the value of consistent definitions in improving comparability across methods, demonstrating the feasibility of using multiple approaches to validate NGHGIs and providing a consistent standard for carbon negotiations at the country level.