# Constraints to Vegetation Growth Reduced by Region-Specific Changes in Seasonal Climate
###### Abstract  
We qualitatively and quantitatively assessed the factors related to vegetation growth using Earth system models and corroborated the results with historical climate observations. The Earth system models showed a systematic greening by the late 21 st century, including increases of up to 100% in Gross Primary Production (GPP) and 60% in Leaf Area Index (LAI). A subset of models revealed that the radiative effects of CO\({}_{2}\) largely control changes in climate, but that the CO\({}_{2}\) fertilization effect dominates the greening. The ensemble of Earth system model experiments revealed that the feedback of surface temperature contributed to 17% of GPP increase in temperature-limited regions, and radiation increase accounted for a 7% increase of GPP in radiation-limited areas. These effects are corroborated by historical observations. For example, observations confirm that cloud cover has decreased over most land areas in the last three decades, consistent with a CO\({}_{2}\)-induced reduction in transpiration. Our results suggest that vegetation may thrive in the starkly different climate expected over the coming decades, but only if plants harvest the sort of hypothesized physiological benefits of higher CO\({}_{2}\) depicted by current Earth system models. terrestrial ecosystems; GPP; LAI; CMIP5; CO\({}_{2}\) fertilization effect; feedback +
Footnote †: journal: Climate  
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underlie the observed greening, including changes in the climate system [8; 9]. Among the mechanisms supporting the greening Earth, CO\({}_{2}\) fertilization is considered the dominant factor in enhancing vegetation, with evidence from free-air CO\({}_{2}\) enrich (FACE) experiments [10], satellite observations [2; 4], and ground observations [11]. Climate change is also substantially contributing to the increase in global vegetation productivity because of the indirect effect of increasing CO\({}_{2}\) concentrations [9]. For instance, global warming is enhancing vegetation growth in high latitudes [12; 13]. As such, each mechanism contributing to vegetation growth has been scrutinized independently, but, in contrast to climate change studies, the global factors affecting vegetation response have not been well studied and summarized. Therefore, the combination and interactions of multiple different climatological and biophysical mechanisms make it difficult to predict the future growth of vegetation at the global scale. As a result, the big discrepancy between modeled and observed sensitivity to CO\({}_{2}\) concentrations is always a source of controversy in the prediction of the future carbon cycle [14]. If climate constrains increase, climate change can cancel the positive effects of CO\({}_{2}\) or of other biogeochemical fertilization (e.g. nitrogen deposition) on vegetation, and possibly accelerate global warming. Therefore, understanding the relative strength of climate variables or increasing CO\({}_{2}\) concentrations, leading to greening or browning of the Earth, is imperative for future projections. We firstly summarized and analyzed the trends in climate and vegetation responding to increasing CO\({}_{2}\) concentrations from the subset of the Coupled Model Intercomparison Project Phase 5 (CMIP5). The CMIP5 dataset includes present run and future projection data produced by Earth system models following several experimental scenarios. Future vegetation growth depends on the type, magnitude, and seasonal timing of climatic changes and their interactions with vegetation physiology.