Fig. 2: A constraint on the sensitivity of global terrestrial photosynthesis to CO₂.

a, The relationship between the modelled sensitivity of GPP to CO₂ (\({\beta }_{{\rm{R}}}^{{\rm{GPP}}}\), TRENDY experiment S1: dynamic CO₂ only) and the modelled cumulative terrestrial carbon sink (PgC, TRENDY experiment S3: dynamic CO₂, climate and land use). Individual TRENDY model details and \({\beta }_{{\rm{R}}}^{{\rm{GPP}}}\) values are listed in Supplementary Table 2. The red line and shaded area show the best linear fit across models and the associated prediction standard error (dashed red) and standard deviation of prediction error (dashed grey) intervals. The vertical dashed lines shows the cumulative residual terrestrial carbon sink (mean, s.d.) between 1982 and 2016 as estimated by the Global Carbon Project²⁷. b, The unconstrained probability density function (PDF) distribution of \({\beta }_{{\rm{R}}}^{{\rm{GPP}}}\) across all original estimates (TRENDY models and the original RS-based approaches; dotted line, grey bars) and the unconstrained PDF of \({\beta }_{{\rm{R}}}^{{\rm{GPP}}}\) across the TRENDY TBMs (dashed black line). The orange area represents the conditional probability distribution derived by applying the constraint from a to the model ensemble.