Increasing CO2 threatens human nutrition

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Abstract
The largest assemblage so far of published data shows that C3 crops have decreased zinc and iron levels under CO2 conditions predicted for the middle of this century, with worldwide nutritional implications. It has been suggested that the concentrations of important nutrients such as zinc and iron in food crops will decrease with increasing atmospheric CO2 levels. However, some studies have not found this, and some of those that have relied on non-field conditions or did not focus on edible crop parts. Samuel Myers et al. have assembled the largest data set to date from free-air CO2 enrichment experiments and find that C3 crops (cereals and grasses) do indeed have reduced zinc and iron levels under the elevated CO2 conditions predicted for the middle of this century. Crops using the C4 photosynthetic pathway are less affected. These findings suggest that breeding cultivars for reduced sensitivity to elevated CO2 may be an important public health priority in many parts of the world. Dietary deficiencies of zinc and iron are a substantial global public health problem. An estimated two billion people suffer these deficiencies1, causing a loss of 63 million life-years annually2,3. Most of these people depend on C3 grains and legumes as their primary dietary source of zinc and iron. Here we report that C3 grains and legumes have lower concentrations of zinc and iron when grown under field conditions at the elevated atmospheric CO2 concentration predicted for the middle of this century. C3 crops other than legumes also have lower concentrations of protein, whereas C4 crops seem to be less affected. Differences between cultivars of a single crop suggest that breeding for decreased sensitivity to atmospheric CO2 concentration could partly address these new challenges to global health.

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