Predicting the impact of changing CO₂ on crop yields: some thoughts on food

Summary Recent breakthroughs in CO 2 fumigation methods using free‐air CO 2 enrichment (FACE) technology have prompted comparisons between FACE experiments and ‘enclosure studies’ with respect to quantification of the effects of projected atmospheric CO 2 concentrations on crop yields. On the basis of one such comparison, it was argued that model projections of future food supply (some of which are based on older enclosure data) may have significantly overestimated the positive effect of elevated CO 2 concentration on crop yields and, by extension, food security. However, in the comparison, no effort was made to differentiate ‘enclosure study’ methodologies with respect to maintaining projected CO 2 concentration or to consider other climatic changes (e.g. warming) that could impact crop yields. In this review, we demonstrate that relative yield stimulations in response to future CO 2 concentrations obtained using a number of enclosure methodologies are quantitatively consistent with FACE results for three crops of global importance: rice ( Oryza sativa ), soybean ( Glycine max ) and wheat ( Triticum aestivum ). We suggest, that instead of focusing on methodological disparities per se , improved projections of future food supply could be achieved by better characterization of the biotic/abiotic uncertainties associated with projected changes in CO 2 and climate and incorporation of these uncertainties into current crop models. Contents Summary 607 I. Rising CO 2 and agricultural crop yields 608 II. Expanding methodologies 608 III. Which methodology gives the ‘truest’ prediction of future yields? 608 IV. Comparing responses among methodologies 610 V. Methodology vs future uncertainty 611 VI. Abiotic uncertainties 612 VII. Biotic uncertainties 613 VIII. Uncertainty vs methodology 614 IX. Modelers and experimentalists 614 X. Final thoughts 615 Acknowledgements 615 References 615