Fig. 2

Relationship between net primary production increments (ΔNPP) and terrestrial carbon accumulation stimulated by atmospheric CO₂ increase in Coupled Model Intercomparison Project (CMIP) Phase 5 (black) and 6 (blue) models based on results from an idealized CMIP5 (Hajima et al. 2014a, 2014b) and CMIP6 (Arora et al. 2020) experiment in which CO₂ concentration was increased every year by 1% and the carbon cycle was assumed to be unaffected by temperature change. Increments were calculated as the difference between the last and first conditions of the experiments. Filled symbols indicate results from models with terrestrial carbon–nitrogen interactions. Solid curve indicates results from the analytical, simple algebraic model based on parameters of CMIP5 models, as proposed by Hajima et al. (2014b). Red ovals indicate results from MIROC series of ESMs