Impact of CO₂ fertilization on maximum foliage cover across the globe's warm, arid environments

Satellite observations reveal a greening of the globe over recent decades. The role in this greening of the "CO₂ fertilization" effect-the enhancement of photosynthesis due to rising CO₂ levels-is yet to be established. The direct CO₂ effect on vegetation should be most clearly expressed in warm, arid environments where water is the dominant limit to vegetation growth. Using gas exchange theory, we predict that the 14% increase in atmospheric CO₂ (1982-2010) led to a 5 to 10% increase in green foliage cover in warm, arid environments. Satellite observations, analyzed to remove the effect of variations in precipitation, show that cover across these environments has increased by 11%. Our results confirm that the anticipated CO₂ fertilization effect is occurring alongside ongoing anthropogenic perturbations to the carbon cycle and that the fertilization effect is now a significant land surface process. Key Points We examine, for a set rainfall, the maximum foliage cover observable by satellite In warm, dry places, such maximum cover has risen by 11% globally (1982-2010) We show a physical and quantitative link between this rise and CO₂ fertilization