Crop models typically suggest that increased temperature and decreased soil moisture will reduce global crop yields by 2050, but that the rising carbon dioxide (CO2) levels will increase plant productivity, thereby offsetting these losses.

However, Long et al explain that the CO2 fertilisation factors used in crop models to project future yields are based on free-air concentration enrichment (FACE) experiments that were conducted over 20 years ago. FACE technology has improved since then, enabling major crops (eg. rice, wheat, soybeans and maize) to now be grown under higher CO2 concentrations in open-air field conditions. Results from these new trials show that elevated CO2 increased yields some 50% less than in previous smaller-scale experiments.

This result casts serious doubt on the projection that rising CO2 will fully offset yield losses due to future warmer, drier conditions. The paper also presents a useful overview of the contribution of FACE experiments to understanding the potential impacts of elevated CO2 levels on crops, and identifies priorities for future FACE research.
(Source: Long, S.P., Ainsworth, E.A., Leakey, A.D.B., Nösberger, J. and Ort, D.R., 2006. Food for thought: lower-than-expected crop yield simulation with rising CO2 concentrations. Science 312: 1918-1921).

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