# Constraints to Vegetation Growth Reduced by Region-Specific Changes in Seasonal Climate
## 3 Results
### Sensitivity Experiments for Climate and Vegetation
Spatially, the ordinal impact on GPP and LAI often reverses between the esmFdbk1 and esmFixClim1 experiments, with much of the Southern Hemisphere switching from a reduction (Figure 10b,c) to an enhancement (Figure 10e,f). Figure 8: Spatial distribution of the additive and counteracting impacts of CO\({}_{2}\) on climate limiting factors. Temperature, (**a**,**d**,**g**); precipitation, **b**,**e**,**h**; and solar radiation, (**c**,**f**,**i**). In order to assess the contribution of radiative and vegetation physiological effects on climate and vegetation, we used an eight-model [highlighted in Table 1] ensemble to compare three CMIP5 experiments, each of which was run for 140 years and experiences a constant CO\({}_{2}\) at pre-industrial levels and/or CO\({}_{2}\) increasing by 1%/year to 4 xCO\({}_{2}\): (1) In the radiative experiment (**a**–**c**), CO\({}_{2}\) increases for the atmosphere but stays constant for vegetation and the carbon cycle and hence the direct effects of CO\({}_{2}\) on plants are suppressed; (2) in the vegetation physiology experiment (**d**–**f**), CO\({}_{2}\) increases by 1%/year to 4 xCO\({}_{2}\) for vegetation and the carbon cycle—thereby reducing stomatal conductance and providing CO\({}_{2}\) fertilization—but stays constant at 280 ppm for the atmosphere and thus the radiative effect is suppressed; (3) in the combined experiment (**g**–**i**), CO\({}_{2}\) concentration increases for the full Earth system. The changes are the mean of the last ten years minus the mean of the first ten years. Stippling indicates that the trend in the 140-year ensemble mean is significant at the 95% level from a Mann–Kendall trend test. For seven out of nine comparisons, the esmFdbk1 and esmFixClim1 experiments produce offsetting impacts on LAI and GPP (Figure 9). The largest differences are in the radiation-limited region, where the esmFdbk1 experiment slightly reduces GPP and the esmFixClim1 experiment increases GPP by as much as 0.15 kg C/m\({}^{2}\)/month in JJA (compare blue and red lines in Figure 9f); LAI changes switch from about \(-\)0.5 to 1.0 (compare blue and red lines in Figure 9i). The temperature-limited region is an exception, where, for both LAI and GPP, the esmFdbk1 and esmFixClim1 experiments are additive (Figure 9m,p). In particular, high northern latitudes are the one clear location where both the esmFdbk1 and esmFixClim1 experiments increase LAI (Figure 10c,f) and GPP (Figure 10b,e), supporting recent conclusions of a strong climate imprint on the broad region of high-latitude during the observational era [36]. The critical role of vegetation physiology is clear in the precipitation-limited region, which experiences the least easing and an almost equal area with precipitation reductions (Figure 1d). But the region also sees a statistically significant increase in simulated equivalent precipitation water in 64% of its area (equivalent to up to 50 mm/month of water in some areas, Figure 1e) and increases in LAI and GPP (Figure 9e,h), in spite of near-zero changes in simulated annual (Figure 4b) and seasonal (Figure 6b) transpiration. While these patterns depict a more efficient use of available water resources and a progressive greening, the physiological response of plants to higher CO\({}_{2}\) in semi-arid regions  
Figure 9: Additive and counteracting impacts of CO\({}_{2}\) on vegetation. Same as Figure 7 except for transpiration, **a–c**; GPP, **d–f**; and LAI, **g-i**. appears to depend on local variations in simulated precipitation, which remain highly uncertain in CMIP5 simulations [37].