## 4 Conclusions and Discussions  
Because of the climatic variability, ecosystem diversity, and topographic complexity, China has large regional discrepancies in response to climate change [31]. It is necessary for the determination of the global warming target to make clear the response of Chinese terrestrial ecosystems to different global warming targets and its regional variations in the future. Our study focused on the potential impacts of 1.5 \({}^{\circ}\)C and 2 \({}^{\circ}\)C increases in global warming on NPP and NEP of terrestrial ecosystems in  
Figure 6: Departure of annual NEP at 1.5 \({}^{\circ}\)C and the 2 \({}^{\circ}\)C warming from values during the reference period under different scenarios. **(a)** 1.5 \({}^{\circ}\)C warming under RCP4.5; **(b)** 2 \({}^{\circ}\)C warming under RCP4.5; **(c)** 1.5 \({}^{\circ}\)C warming under RCP8.5; **(d)** 2 \({}^{\circ}\)C warming under RCP8.5. Positive values represent NEP increase, and vice versa. China by using an ensemble of the simulations of four ESMs in CMIP5 and a process-based ecosystem model (CEVSA2 model) under two representative concentration pathways. The main conclusions and discussions are as follows. NPP and NEP in China are Projected to Increase Both at 1.5 \({}^{\circ}\)C and 2 \({}^{\circ}\)C Global Warming  
Continuous warming was projected to increase both NPP and NEP of terrestrial ecosystems in China at 1.5 \({}^{\circ}\)C or 2 \({}^{\circ}\)C global warming. Both NPP and NEP were projected to have significant increasing trends (\(p<0.01\)). The increment of NPP would be approximately 13% at 1.5 \({}^{\circ}\)C and 19% at 2 \({}^{\circ}\)C warming. Terrestrial NPP in China is very likely to increase with global warming, and it is projected to increase continuously both at 1.5 \({}^{\circ}\)C and 2 \({}^{\circ}\)C global warming. This result is consistent with most previous modeling studies of climate change impacts on China's terrestrial ecosystem NPP [8; 46; 47]. At the global scale, the gross primary productivity (GPP) and NPP were projected to increase or remain unchanged, especially in mid- to high-latitudes [9; 10; 48]. Overall, the change of NPP would depend on the regions and vegetation types [49]. Other analyses based on CMIP5 models also found that the terrestrial ecosystem NPP would increase globally, and the spatial increment of annual NPP in China is similar to our study [50]. Additional 0.5 \({}^{\circ}\)C Warming Will Depress the Increase Rate of NPP and Carbon Uptake Capacity under the RCP4.5 Scenario  
The model simulations suggest that the increasing rate of NPP would decline at 2 \({}^{\circ}\)C compared with that at 1.5 \({}^{\circ}\)C under RCP4.5. Both the increasing rates and mean values of NEP would decline under a lower emission scenario, but the increasing rates would decline more significantly under high emission scenarios. About 81% of study areas show a declined increase rate of NPP at 2 \({}^{\circ}\)C compared with that at 1.5 \({}^{\circ}\)C under the RCP4.5 scenario. Although most areas of China act as carbon sinks in the future under both scenarios, some areas of northern China and Qinghai-Tibet Plateau would show a decline of net carbon uptake. This suggests that continuous global warming under a lower emission scenario should not only influence the increase of NPP but also depress the ecosystem capacity of carbon sequestration in some regions significantly. Rising temperature promotes the growth of plants as well as the respiration of plants and soils [51]. Although the warming trends were projected to be widespread in most parts of China, spatial patterns in precipitation would vary greatly (Figures 7 and 8). The increase of temperature was estimated to be the dominant factor accounting for NPP changes at national scale [20; 30; 52]. Relatively higher increases in temperature and precipitation would occur in northern China compared to southern China partially because northwestern China and Qinghai-Tibet Plateau have lower mean annual temperature, and higher sensitivity to the global warming [53].