Impact of CO 2 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 “CO 2 fertilization” effect—the enhancement of photosynthesis due to rising CO 2 levels—is yet to be established. The direct CO 2 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 CO 2 (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 CO 2 fertilization effect is occurring alongside ongoing anthropogenic perturbations to the carbon cycle and that the fertilization effect is now a significant land surface process.