## 4 Conclusions  
To evaluate the GPP change under 1.5 and 2 \({}^{\circ}\)C of global warming, this study selected three CMIP6 ESMs (i.e., BCC-CSM2-MR, CMCC-CM2-SR5, and MPI-ESM1-2-HR) that performed well in historical GPP modeling; the principal conclusions derived are as follows:  
1. Under 1.5 and 2 \({}^{\circ}\)C of global warming, the projections of the ESMs indicate that global warming introduces no ecological risk in China. Although certain individual grid points showed negative GPP changes, regional GPP showed a marked increase, the smallest magnitude of which was more than 10% greater than that from 1986 to 2005. 2. Specifically under 1.5 \({}^{\circ}\)C warming, the GPP in the temperate continental zone is projected to increase by 16.1-23.8% in comparison with the historical value (1986-2005). Figure 6: Climate contributions to GPP change with the different ESMs under (**a**) 1.5 and (**b**) 2 \({}^{\circ}\)C of global warming. Bars represent the absolute climate contributions (PgC yr\({}^{-1}\)). Percentages represent the relative climate contributions to the overall GPP changes. Similarly, GPP is projected to increase by 12.3-16.1% in the temperate monsoonal zone, 12.5-14.7% in the subtropical-tropical monsoonal zone, and 20.0-37.0% on the Tibetan Plateau. Under 2 \({}^{\circ}\)C warming, the increase in GPP is projected to be even greater--i.e., 23.0-34.3% in the temperate continental zone, 21.2-24.4% in the temperate monsoonal zone, 16.1-28.4% in the subtropical-tropical monsoonal zone, and 28.4-63.0% on the Tibetan Plateau. 3. Climate change is projected to contribute positively to GPP change, except in the temperate continental zone with MPI-ESM1-2-HR. Although precipitation has larger sensitivity parameters, temperature generally plays a more important role in GPP change because of the larger change relative to its own variability in comparison with that of precipitation. The output of the three studied ESMs showed a marked spread, not only in GPP change but also in the accountability of climate to the ecosystem. In addition, the change in climate, especially precipitation, differed strongly within the models, which indicates the large uncertainty in the climate projections of the ESMs. All of these add to difficulties in attributing future GPP change to climate. Moreover, this study analyzed the influence of annual precipitation and temperature upon the ecosystem productivity. However, GPP variation depends not only on these, but also on wind speed, humidity, solar radiation, nitrogen deposition, etc. Future studies should be more comprehensive in building the regressed equations between GPP and the impact factors. This study failed to analyze the contribution of CO\({}_{2}\) to the GPP increase. This was due to the lack of gridded/regional CO\({}_{2}\) concentration data. Future research should take into account the CO\({}_{2}\) effect when analyzing the GPP change and be more specific about vegetation of C3 and C4 types. This study is more general in that it focuses on the general productivity of the climate zones. Future studies should be refined to specific vegetation covers, such as forest, grass, etc. The fact that different ESMs lack consensus in the response mechanism of the ecosystem to climate, even over one specific climate zone, highlights that there is still a long way for ecological modeling in China to go. Conceptualization, C.Z. and Y.D. ; formal analysis, C.Z. and Y.D. ; writing--original draft preparation, C.Z. ; review and editing, Y.D., S.W. and J.C. All authors have read and agreed to the published version of the manuscript. This work was funded by the National Key Research and Development Program of China (2018 YFC1509003, 2019 YFC0507802, and 2018 YFC1508902), and the Strategic Priority Research Program of Chinese Academy of Sciences (XDA19040304). This study was performed through the Institute of Geographic Sciences and Natural Resources Research (IGSNRR). We also appreciate the support from the Coupled Model Intercomparison Project (phase 6) for providing the ESM outputs.