Food for Thought: Lower-Than-Expected Crop Yield Stimulation with Rising CO 2 Concentrations

Model projections suggest that although increased temperature and decreased soil moisture will act to reduce global crop yields by 2050, the direct fertilization effect of rising carbon dioxide concentration ([CO 2 ]) will offset these losses. The CO 2 fertilization factors used in models to project future yields were derived from enclosure studies conducted approximately 20 years ago. Free-air concentration enrichment (FACE) technology has now facilitated large-scale trials of the major grain crops at elevated [CO 2 ] under fully open-air field conditions. In those trials, elevated [CO 2 ] enhanced yield by ∼50% less than in enclosure studies. This casts serious doubt on projections that rising [CO 2 ] will fully offset losses due to climate change.