## 3 Results
### Latitudinal Trends of NDVI and Modeled NPP  
The latitudinal pattern of both NDVI and NPP trends are important in overall understanding of the role of terrestrial ecosystems in carbon cycle, and their contribution and sensitivity to climate conditions. We found the maximum and minimum latitudinal NPP trend for the period of 1982-2012 to be \(\sim\)0.10 Pg \(\mathrm{C}\cdot\mathrm{y}^{-1}\cdot\mathrm{y}^{-1}\) and \(\sim\)\(-\)0.047 Pg \(\mathrm{C}\cdot\mathrm{y}^{-1}\cdot\mathrm{y}^{-1}\), respectively. Similarly, the maximum and minimum latitudinal NDVI trends were \(\sim\)0.035 y\({}^{-1}\) and \(\sim\)\(-\)0.016 y\({}^{-1}\), respectively. Generally, both NPP and NDVI trends showed similar patterns (Figure 6), however, the level of consistency to such patterns differed substantially for different latitudes. The larger NPP and NDVI trends were observed predominantly in the Tropics, followed by Boreal, Temperate, and Extra Tropic regions. In the Tropics, models showed higher degree of variability in NPP compared to other regions. The best agreements between NPP and NDVI trends were obtained for the Temperate and Boreal regions, while, the major discrepancy between the two was observed in the 40 S-60 S zone of Extra Tropics region.  
Considering the simulated NPP trends from individual models, JULES showed larger NPP trend values compared to other models (Figure 7). The highest NPP trend value in JULES was \(\sim\)0.24 Pg \(\mathrm{C}\cdot\mathrm{y}^{-1}\cdot\mathrm{y}^{-1}\) compared to the second highest value of \(\sim\)0.14 Pg \(\mathrm{C}\cdot\mathrm{y}^{-1}\cdot\mathrm{y}^{-1}\) from OCN. We observed decreasing NPP trends by all five models, especially in Extra Tropics and specifically 20 S-40 S zone, followed by Temperate regions and specifically the 20 N-40 N zone. The highest decreasing NPP trends of \(\sim\)\(-\)0.1 Pg \(\mathrm{C}\cdot\mathrm{y}^{-1}\cdot\mathrm{y}^{-1}\) and \(-\)0.07 Pg \(\mathrm{C}\cdot\mathrm{y}^{-1}\cdot\mathrm{y}^{-1}\) were observed for JULES and LPJ models, respectively. However, for certain zones the trend was more prominent compared to other zones. For example, the decreasing trends of both NPP and NDVI were consistent in Temperate regions and specifically the 20 N-40 N zone. The VEGAS model showed relatively consistent (with  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Spatial Unit** & **CLM4.5** & **JULES** & **LPJ** & **OCN** & **VEGAS** & **MME** \\ \hline Global & 0.59 & 0.61 & 0.60 & 0.66 & 0.67 & 0.64 \\ Boreal & 0.64 & 0.64 & 0.63 & 0.71 & 0.68 & 0.69 \\ Temperate & 0.72 & 0.56 & 0.50 & 0.73 & 0.67 & 0.73 \\ Tropics & 0.42 & 0.49 & 0.50 & 0.49 & 0.50 & 0.50 \\ Extra Tropics & 0.44 & 0.50 & 0.48 & 0.67 & 0.57 & 0.59 \\ \hline \end{tabular}
\end{table}
Table 5: Correlation coefficients between NDVI and modeled NPP at global and regional levels along with their statistical significance level (\(p<0.05\)).  
Figure 6: A latitudinal comparison of simulated NPP and observed NDVI trends. The thick black line represents the TRENDY multi-model ensemble, and the shaded gray area captures the models’ spread.  
lower variations) NPP trends throughout all latitudinal regions/zones. The NPP values from the CLM4.5, LPJ and OCN models were in close agreement.