High CO2 Expands Where Plants Can Grow in CESM‐CLM4‐CNDV

As anthropogenic carbon emissions continue, it is important to predict how vegetation will change due to the warming climate, increasing atmospheric CO2, and changing precipitation patterns. Some projections show decreases in vegetation either regionally in the tropics (e.g., Falloon et al., 2012; Port et al., 2012) or globally (e.g., Bastin et al., 2019) due to high temperatures and drying, and there is large uncertainty surrounding the response of global vegetation to climate change (Arora et al., 2020; Friedlingstein et al., 2006; Walker et al., 2020). Here we use simulations with the NCAR Community Earth System Model (CESM) with dynamic vegetation to explore how increasing CO2 may affect vegetation and, through feedbacks, the climate. We find that globally, warming only decreases vegetation, but when we include the effects of CO2 on plant physiology, vegetated area increases by ∼23% relative to the preindustrial simulation. This greening occurs even without significant increases in precipitation, as high CO2 increases plant water use efficiency, allowing for more vegetation in arid and hot regions. Our results show that CO2‐induced vegetation changes affect climate by amplifying high latitude warming, cooling some areas of the tropics, and shifting global precipitation patterns. Our results highlight the importance of including climate‐vegetation feedbacks in Earth system modeling.