This dataset includes the processed environmental input data to run the C3/C4 competition model and the simple carbon cycle model over 1982-2016 used in Lavergne et al. (2025): 1979_2018_Tdaytime.nc, elev.nc, d13co2_annmean_0.5_1982_2016.nc, co2_annmean_0.5_1982_2016.nc, modis_snowandice_0.5d-2010.nc, modis_barren_sparsely_vegetated_0.5d-2010.nc We provide the global annual outputs from the P model for the historical simulations (pmodel_outputs_modern.nc) and for the attribution analyses (pmodel_outputs_modern_co2_effect.nc, pmodel_outputs_modern_temp_effect.nc, pmodel_outputs_modern_vpd_effect.nc, pmodel_outputs_modern_theta_effect.nc). We also provide the global annual outputs from the C3/C4 model and the simple carbon cycle model over 1982-2016. The predicted fraction of C4 plants (F4), plant carbon isotopic discrimination (D13C) and gross primary production (GPP) for natural ecosystems and both natural and crops are available at C3C4_model_outputs.nc. The stable carbon isotopic composition of atmospheric CO2 for different configurations of the model are available at Simus_constant_delta_constant_fracc4_K2017.mat, Simus_variable_delta_constant_fracc4_K2017.mat, Simus_constant_delta_constant_fracc4_L2025.mat, Simus_variable_delta_constant_fracc4_L2025.mat, Simus_variable_delta_variable_fracc4_L2025.mat Please refer to https://github.com/Alielav/Comms-Earth-Lavergne-et-al.-2025 and manuscript for more details: Lavergne, A., Harrison, S.P., Atsawawaranunt, K., Dong, N., Prentice, I.C. (2025) Minimal impact of recent decline in C4 vegetation abundance on atmospheric carbon isotopic composition, Communications Earth & Environment