Increasing CO₂ threatens human nutrition

Study in one sentence

This study found that elevated atmospheric carbon dioxide (CO₂) concentrations, expected by mid-century, significantly reduce the protein, iron, and zinc content of major food crops, potentially increasing the risk of nutrient deficiencies for hundreds of millions of people worldwide.

Publication and date

The study, titled “Increasing CO₂ threatens human nutrition,” was published in the peer-reviewed scientific journal Nature on May 7, 2014. The lead author is Samuel S. Myers, with co-authors from institutions including the Harvard T.H. Chan School of Public Health, the University of Illinois, and the University of California, Davis.

Research question

The researchers set out to answer: How do elevated atmospheric CO₂ concentrations—comparable to those expected by the middle of this century—affect the protein, iron, and zinc content of staple food crops, and what are the potential implications for human nutrition globally?

Method

The study combined experimental data with dietary intake modeling. First, the team grew 41 cultivars of six C3 grain and legume crops (wheat, rice, field peas, soybeans, maize, and sorghum) under elevated CO₂ conditions (546–586 ppm) using Free-Air CO₂ Enrichment (FACE) technology, which simulates future atmospheric conditions in open fields. They measured changes in protein, iron, and zinc concentrations compared to crops grown at ambient CO₂ levels. Next, they used global food supply data from the United Nations Food and Agriculture Organization (FAO) and dietary intake surveys to estimate the impact of these nutrient reductions on the populations of 151 countries, focusing on the risk of zinc and iron deficiency and protein intake adequacy.

Main findings

Under elevated CO₂, significant nutrient declines were observed in C3 crops (wheat, rice, soybeans, field peas), while C4 crops (maize, sorghum) showed no significant changes. For C3 crops, the average reductions were: zinc –5% to –9%, iron –4% to –5%, and protein –4% to –8% across different crops. Wheat experienced the largest declines: zinc –9.3%, iron –5.1%, protein –6.3%. Rice showed zinc –3.3%, iron –5.2%, protein –7.8%. Soybeans had zinc –5.1%, iron –4.1%, protein –4.1%. The modeling estimated that these nutrient losses could place an additional 138 million people at risk of zinc deficiency by 2050. Moreover, 1.4 billion women of childbearing age and children under 5 live in countries where current dietary iron intake is already low, and the projected CO₂-induced reductions could cause them to lose more than 4% of their dietary iron supply. Protein losses could also exacerbate protein inadequacy in regions where intake is marginal, such as parts of South Asia and sub-Saharan Africa.

What the findings do not prove

The study does not prove that climate change will definitely cause widespread malnutrition; it models a potential future scenario based on current dietary patterns and CO₂ projections. It does not account for possible adaptations such as changes in crop varieties, dietary shifts, food fortification, or supplementation programs. The findings show a correlation between elevated CO₂ and reduced nutrient density in crops, but they do not directly measure health outcomes in human populations. The study also does not assess the full range of nutrients or the complex interactions within food systems that could mitigate or worsen the effects.

Limitations

The FACE experiments were conducted on a limited number of crop cultivars and in specific geographic locations, which may not represent all growing conditions or genetic diversity. The dietary modeling relied on national-level food supply data, which can mask within-country variation in consumption and nutrient intake. The study focused only on protein, iron, and zinc, omitting other nutrients that might also be affected. It did not consider the potential effects of other climate change factors such as temperature increases, water stress, or ozone levels, which could further alter crop nutrient content. The projections assume static diets and no adaptive responses, which is unlikely over the coming decades.

How it compares with previous research

Earlier studies had shown that elevated CO₂ can reduce protein and mineral concentrations in plants, but this was the first to combine extensive FACE data with global dietary modeling to quantify the human health burden. The findings align with prior experimental work on CO₂ and plant nutrition, but extend the implications to public health. Subsequent research, including a 2018 study by Smith and Myers in GeoHealth, confirmed that CO₂-induced nutrient declines could exacerbate global anemia burdens. The study also complements broader climate-food security literature by highlighting a nutritional dimension beyond calorie availability, which had been the primary focus of earlier assessments like those by the Intergovernmental Panel on Climate Change (IPCC).

Why it matters

This research reveals a hidden consequence of climate change: even if crop yields remain stable, the nutritional quality of staple foods may decline, silently increasing the risk of “hidden hunger” (micronutrient deficiencies). It underscores the need for agricultural and public health strategies to address nutrient losses, such as breeding nutrient-dense crops, enhancing soil management, and expanding food fortification. The study also provides a critical evidence base for policymakers to consider nutrition when setting climate targets and for the inclusion of dietary health in climate impact assessments.

Link to the primary paper

Myers, S. S., Zanobetti, A., Kloog, I., Huybers, P., Leakey, A. D. B., Bloom, A. J., Carlisle, E., Dietterich, L. H., Fitzgerald, G., Hasegawa, T., Holbrook, N. M., Nelson, R. L., Ottman, M. J., Raboy, V., Sakai, H., Sartor, K. A., Schwartz, J., Seneweera, S., Tausz, M., & Usui, Y. (2014). Increasing CO₂ threatens human nutrition. Nature, 510(7503), 139–142. https://doi.org/10.1038/nature13179