## 3 Results and Discussion
### Changes of NPP in the Future  
The total simulated NPP under different climate scenarios from 2017 to 2100 are shown in Table 3. Overall, the total NPP of China will continue to increase in the future under different climate change scenarios with increasing CO\({}_{2}\) concentration and temperatures. The total NPP under the A2 and RCP85 scenarios would be significantly higher than those under the B1 and RCP45 scenarios, and the magnitude of deviation between them would be more remarkable after 2050. The average CO\({}_{2}\) concentrations and temperatures under the A2 and RCP85 scenarios would be approximately 18.4 ppm and 20.2 ppm and 0.18 \({}^{\circ}\)C and 0.31 \({}^{\circ}\)C, respectively, higher than those under the B1 and RCP45 scenarios during 2011-2050. On average, total NPP would be just 0.01 Pg C yr\({}^{-1}\) and 0.04 Pg C yr\({}^{-1}\) higher under A2 and RCP85 scenarios than that under B1 and RCP45 scenarios during 2011-2050. When the gaps of CO\({}_{2}\) concentrations and temperatures would increase to 175.0 ppm and 236.6 ppm and to 1.79 \({}^{\circ}\)C and 1.69 \({}^{\circ}\)C during 2051-2100, the gaps of the total NPP would widen to 0.48 Pg C yr\({}^{-1}\) and 0.66 Pg C yr\({}^{-1}\). Especially in the final period (2091-2100), the average total NPP in the A2 and RCP85 scenarios would \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Code** & **Types** & **Latitude** & **Longitude** & **Period** & **GPPobs** & **LPJsim** & **RPE\%** \\ \hline DHS & Forest & 23.17 & 112.53 & 2003–2008 & 1367.26 \(\pm\) 78.42 & 1953.98 & 42.91\% \\ QYZ & Forest & 26.73 & 115.05 & 2003–2008 & 1798.74 \(\pm\) 100.44 & 1926.07 & 7.08\% \\ CBS & Forest & 42.40 & 128.10 & 2003–2008 & 1338.84 \(\pm\) 108.86 & 1437.48 & 7.37\% \\ HZ & Forest & 51.78 & 123.02 & 2010 & 962.75 & 1133.02 & 17.69\% \\ XSBN & Forest & 21.95 & 101.20 & 2003–2008 & 2342.67 \(\pm\) 174.10 & 2020.26 & \(-\)13.76\% \\ ALS & Forest & 24.53 & 101.02 & 2009–2010 & 1848.33 & 1791.98 & \(-\)3.05\% \\ LS & Forest & 45.33 & 127.67 & 2004 & 1351 & 1472.64 & 9.00\% \\ YY & Forest & 29.53 & 112.86 & 2006–2007 & 1974.8 & 1948.72 & \(-\)1.32\% \\ AQ & Forest & 30.47 & 116.99 & 2006–2007 & 1859.2 & 1948.23 & 4.79\% \\ XP & Forest & 33.35 & 113.91 & 2010 & 1288.1 & 1425.93 & 10.70\% \\ YC & Cropland & 36.83 & 116.57 & 2003–2008 & 1746.62 \(\pm\) 139.35 & 1250.08 & \(-\)28.43\% \\ TYC & Cropland & 44.57 & 122.92 & 2004–2006 & 444.33 \(\pm\) 56.36 & 356.00 & \(-\)19.88\% \\ WS & Cropland & 36.65 & 116.05 & 2007–2008 & 1838 & 1208.18 & \(-\)34.27\% \\ NM & Grassland & 44.53 & 116.67 & 2004–2008 & 231.66 \(\pm\) 111.13 & 329.27 & 42.13\% \\ XLD & Grassland & 43.55 & 116.67 & 2006 & 294.44 & 392.83 & 33.42\% \\ SY & Grassland & 34.35 & 100.55 & 2006 & 480.27 & 701.13 & 45.99\% \\ DTZ & Wetland & 31.58 & 121.90 & 2005 & 1512.63 & 1704.31 & 12.67\% \\ PJ & Wetland & 41.13 & 121.90 & 2005 & 1298.16 & 1371.52 & 5.65\% \\ \hline \hline \end{tabular} Note: RPE means Relative Predictive Error and is calculated as (LPJsim-GPPobs)/ GPPobs \(\times\)100%.  
\end{table} 
Table 4: Comparison of annual GPP simulated by LPJ with observations. Figure 8: Locations of flux towers with measured GPP for validating simulated GPP (**left**) and the scatter plot of simulated GPP and observations (**right**). reach 4.90 Pg C yr\({}^{-1}\) and 5.10 PgC yr\({}^{-1}\), which would be 0.70 Pg C yr\({}^{-1}\) and 1.20 PgC yr\({}^{-1}\) larger than that under the B1 and RCP45 scenarios. As shown in Table 5 and Figure 9, there are differences in annual total simulated NPP using the climates projected by different climate models (NCAR and CNRM). The average NPP simulated using the climates projected by two climate models during the periods of 2011-2010, 2046-2055, and 2091-2100 was used to indicate the NPP changes in the early, middle, and late stages, respectively. The results showed that forests would make significant contributions to increases in NPP in the future. In most temperate forests, the NPP would experience a sustained increase.