## 3 Results
### Temporal Trends of NDVI and Modeled NPP  
The global mean NDVI was estimated to be 0.33 with an increasing trend of 0.00041 y\({}^{-1}\) for the period of 1982-2012 (Table 3). At the regional level, Tropics showed substantially higher NDVI (0.43) followed by Temperate (0.30), Boreal (0.27) and Extra Tropic (0.19) regions. Despite the highest NDVI  
Figure 3: The relation between NDVI and modeled NPP from TRENDY models for the period of 1982–2012. Figure 2: The multi-decadal and global pattern of simulated NPP trends for 1982–2012 period, based on five TRENDY models described in Table 1.  
value in Tropics, maximum trend in NDVI increase (0.00052 y\({}^{-1}\)) was observed for Temperate regions. With the exception of Extra Tropics, all other regions showed a statistically significant increase of NDVI during 1982-2012 periods. The global NPP was estimated to be about 63 Pg C\(\cdot\) y\({}^{-1}\), with an increase of 0.214 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\) (Table 2). Among the five models, JULES produced the highest global NPP (72.4 Pg C\(\cdot\) y\({}^{-1}\)) compared to lowest NPP (53.7 Pg C\(\cdot\) y\({}^{-1}\)) by LPJ. The global NPP estimate of about 62.9 Pg C\(\cdot\) y\({}^{-1}\) by VEGAS corresponds closely with the models mean ensemble (MME). The maximum global NPP increase of 0.359 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\) was produced by JULES followed by OCN (0.238 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\)). At regional level, Tropics showed the highest NPP (36.24 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\)) followed by Temperate (13.55 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\)), Boreal (9.68 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\)) and Extra Tropical (3.44 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\)) regions, respectively. However, the maximum NPP increase was observed in the Boreal (0.051 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\)) region, as compared with all other regions. The magnitude of simulated NPP varied also among five models, for different regions. For example, JULES produced maximum NPP in the Tropics (42.80 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\)) and in Boreal (11.42 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\)) regions with corresponding increases of 0.237 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\) and 0.080 Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\), respectively. Overall, all models showed an increasing trends in NPP across all regions, except LPJ which showed a negative trend in Extra Tropics; however, this trend was not statistically significant. Individual models' estimates of NPP and their trends for different regions are presented in Table 4. \begin{table}
\begin{tabular}{c c c c} \hline \multicolumn{4}{c}{**Global**} \\ \hline
**Models** & **NPP (Pg C\(\cdot\) y\({}^{-1}\))** & **Trend (Pg C\(\cdot\) y\({}^{-1}\). y\({}^{-1}\))** & **SE** \\ \hline MME & 62.90 & 0.214 ** & 0.03 \\ CLM4.5 & 64.75 & 0.184 ** & 0.02 \\ JULES & 72.4 & 0.359 ** & 0.05 \\ LPJ & 53.72 & 0.148 ** & 0.03 \\ OCN & 60.78 & 0.238 ** & 0.03 \\ VEGAS & 62.85 & 0.141 ** & 0.02 \\ \hline  & \multicolumn{2}{c}{Boreal (50 N\({}^{-90}\) N)} \\ MME & 9.68 & 0.051 ** & 0.06 \\ CLM4.5 & 9.39 & 0.038 ** & 0.06 \\ JULES & 11.42 & 0.080 ** & 0.08 \\ LPJ & 11.33 & 0.042 ** & 0.07 \\ OCN & 9.19 & 0.050 ** & 0.07 \\ VEGAS & 7.06 & 0.043 ** & 0.08 \\ \hline \end{tabular}
\end{table} 
Table 4: Spatial features of modeled NPP at global and regional levels along with their trend rates and statistical significance level and standard error (SE). \begin{table}
\begin{tabular}{c c c} \hline
**Spatial Unit** & **Trend (NDVI\(\cdot\) y\({}^{-1}\))** & **SE** \\ \hline Global & 0.00041 ** & 0.03 \\ Boreal & 0.00038 ** & 0.03 \\ Temperate & 0.00052 ** & 0.03 \\ Tropics & 0.00048 ** & 0.03 \\ Extra Tropics & 0.00011 * & 0.04 \\ \hline \end{tabular}  
**shows where \(p\) < 0.01 and * shows where \(p\) < 0.05.**  
\end{table} 
Table 3: The global and regional trend rates of NDVI, with associated level of statistical significance and standard error (SE). The computed NDVI trend rates are benchmarked to the year 1982.