Climate uncertainty begets overestimation of Chinese natural carbon sinks

Changes in terrestrial carbon (C) balance under climate change continue to pose significant uncertainties in regional C budgets, leading to a lack of consensus on C balance and challenges in benchmarking. Here we investigate the spatiotemporal patterns and the potential drivers of China’s terrestrial C cycle and its covariation with climate from 1979 to 2014 using three atmospheric forcings and by an ecosystem model and a machine learning model. We estimate Gross Primary Productivity (GPP) over China ranging from 6.52 to 7.89 PgC yr-1, with a clear gradient from southeast to northwest. China is a weak C sink (0.01±0.01 PgC yr-1), indicating a previously overestimated natural carbon sink in China. The total carbon pool in China is estimated to be within the range of 86.30–90.00 PgC, with 84.1% stored in soil and 15.9% (10.17–14.04 PgC) in vegetation. Vegetation C sequestration  is estimated to offset 37%–50% of China’s anthropogenic emissions over that period. Forests, shrublands, grasslands, and croplands contribute significantly to this sequestration, with carbon storage values of 30.83–38.41 Pg C, 2.47–3.07 Pg C, 25.67–44.32 Pg C, and 2.52–3.5 Pg C, respectively. Our findings underscore the dominant influence of climatic factors in shaping the land C cycle, surpassing the impact of land use. The findings emphasize the need for China to prioritize industrial emission reductions for global carbon management and climate change strategies, emphasizing the pivotal role of its terrestrial C sinks.