## 4 Discussion  
Our findings indicate that global climate change impacts GPP negatively, which aligns with the results from the study by [PERSON] et al. [55], and the implementation of carbon-neutral PER policies enhances vegetation carbon uptake in China (see Figure 1). Some studies have provided evidence for the positive impact of PER on GPP by examining the effects of aerosol and O\({}_{3}\) reduction on vegetation growth. For instance, [PERSON] et al. found that reducing aerosol concentrations by 2030 benefits ecosystems [56]. [PERSON] et al. indicated that lowering O\({}_{3}\) levels under the carbon neutrality goal will mitigate crop yield reductions caused by global climate change [57]. Furthermore, it is observed that aerosol radiative effects play a crucial role in promoting increased GPP under carbon-neutral PER policies. These effects are predominantly influenced by temperature variations during winter and shortwave radiation changes throughout other seasons. Specifically, the changes in Tmin and Srad during January mitigate the adverse effects of low temperatures on vegetation [58], while the increase in Srad enhances the availability of PAR for plants. From a nationwide perspective, most regions within China have experienced an increase in GPP due to carbon-neutral PER policies (see Figure 3). Spatially, this enhancement is primarily concentrated in southwestern China and eastern China regions, where GPP is significantly affected by aerosols [59].  
Several defects increase the uncertainties of GPP in this study. Firstly, the omission of considering the increase in atmospheric CO\({}_{2}\) concentration, despite its significant effects on the terrestrial carbon cycle [60; 61; 62], may lead to an underestimation of the decline in GPP caused by global climate change in 2060. The fertilization effect of elevated CO\({}_{2}\) levels on photosynthesis and vegetation growth is well recognized; however, it is important to note that this effect diminishes over time and may even shift towards a negative impact on GPP in the near future [12; 13]. Therefore, the absence of the effect of CO\({}_{2}\) rise may underestimate the decline of GPP caused by global climate change in 2060, emphasizing the imperative role of offsetting from PER. Secondly, due to uncertainties associated with projected meteorological parameters, the reliability of estimated future GPP is limited. This study relies exclusively on data from the MPI-ESM1-2-HR model as a climate background field due to its favorable overall performance across evaluations of CMIP6 models [63]. However, there are evident discrepancies among different CMIP6 model data which can significantly affect simulation outputs for GPP. To assess this issue, meteorological data from 2016 of the other three CMIP6 models (see Table S5) are used for calculating China's GPP and compared against benchmark data (the MYD17A2H dataset). As shown in Table S6, results driven by the MPI-ESM1-2-HR model outperform those obtained using the other three CMIP6 models. Finally, current models used for estimating GPP exhibit substantial uncertainties [64; 65]. The simplified models like MODIS-PSN can capture variations caused by meteorological parameters accurately enough; they failed to consider future changes in surface physical conditions or geochemical and physiological factors. Notably, PER-induced declines in O\({}_{3}\) concentrations might promote future increases in GPP [57], which have not been accounted for yet.