Rising atmospheric CO₂ concentrations threaten human nutrition by reducing the zinc and iron content in C₃ crops like wheat, rice, and legumes. A meta-analysis of data from 143 comparisons across seven FACE experiments in Japan, Australia, and the US shows that elevated CO₂ levels lead to significant decreases in zinc and iron in C₃ crops, with wheat showing a 9.3% decrease in zinc and 5.1% in iron. C₃ grasses also experience reduced protein content, while C₄ crops are less affected. Phytate levels in wheat decrease significantly, potentially offsetting some zinc loss. These findings suggest that future CO₂ levels could reduce the nutritional value of key crops, increasing the risk of zinc and iron deficiencies in populations reliant on C₃ grains and legumes. Over 2.3 billion people depend on these crops for at least 60% of their dietary zinc and iron, and 1.9 billion for 70% or more. Breeding programs to reduce crop sensitivity to elevated CO₂ could help mitigate these effects, but challenges remain in terms of affordability and farmer preferences. The study also highlights the need for further research into the mechanisms behind nutrient dilution and the development of biofortified crops. The implications of these findings underscore the importance of addressing CO₂ emissions and improving crop nutrition to ensure global food security.Rising atmospheric CO₂ concentrations threaten human nutrition by reducing the zinc and iron content in C₃ crops like wheat, rice, and legumes. A meta-analysis of data from 143 comparisons across seven FACE experiments in Japan, Australia, and the US shows that elevated CO₂ levels lead to significant decreases in zinc and iron in C₃ crops, with wheat showing a 9.3% decrease in zinc and 5.1% in iron. C₃ grasses also experience reduced protein content, while C₄ crops are less affected. Phytate levels in wheat decrease significantly, potentially offsetting some zinc loss. These findings suggest that future CO₂ levels could reduce the nutritional value of key crops, increasing the risk of zinc and iron deficiencies in populations reliant on C₃ grains and legumes. Over 2.3 billion people depend on these crops for at least 60% of their dietary zinc and iron, and 1.9 billion for 70% or more. Breeding programs to reduce crop sensitivity to elevated CO₂ could help mitigate these effects, but challenges remain in terms of affordability and farmer preferences. The study also highlights the need for further research into the mechanisms behind nutrient dilution and the development of biofortified crops. The implications of these findings underscore the importance of addressing CO₂ emissions and improving crop nutrition to ensure global food security.