*Article* **Constraints to Vegetation Growth Reduced by Region-Specific Changes in Seasonal Climate**

**Hirofumi Hashimoto 1,\*, Ramakrishna R. Nemani 2, Govindasamy Bala 3, Long Cao 4, Andrew R. Michaelis 1, Sangram Ganguly 5, Weile Wang 1, Cristina Milesi 6, Ryan Eastman 7, Tsengdar Lee <sup>8</sup> and Ranga Myneni <sup>9</sup>**


Received: 31 October 2018; Accepted: 10 January 2019; Published: 1 February 2019

**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 21st 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 CO2 largely control changes in climate, but that the CO2 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 CO2-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 CO2 depicted by current Earth system models.

**Keywords:** terrestrial ecosystems; GPP; LAI; CMIP5; CO2 fertilization effect; feedback
