Rising CO2 Poses Major Threat to Human Nutrition, Study Says

Crops that provide dietary zinc and iron will have significantly reduced concentrations of those nutrients by 2050.


agriculture fields image via shutterstock

Approximately two billion people suffer from zinc and iron deficiencies, according to the Harvard School of Public Health (HSPH). That’s why it’s alarming that a new study published by HSPH researchers in the journal, Nature, found that elevated levels of atmospheric CO2 (levels that are anticipated by the year 2050), will have caused a significant decline in the concentration of nutrients in crops, particularly those that provide a large amount of the global population with most of their dietary zinc and iron needs.

The reduction in these nutrients represents the most significant health threat ever shown to be associated with climate change, the study says.

“This study is the first to resolve the question of whether rising CO2 concentrations—which have been increasing steadily since the Industrial Revolution—threaten human nutrition,” says Samuel Myers, research scientist in the Department of Environmental Health at HSPH and the study’s lead author.

According to the study:

The researchers analyzed data involving 41 cultivars (genotypes) of grains and legumes from the C3 and C4 functional groups (plants that use C3 and C4 carbon fixation) from seven different locations in Japan, Australia, and the United States. The level of CO2 across all seven sites was in the range of 546-586 parts per million (ppm). They tested the nutrient concentrations of the edible portions of wheat and rice (C3 grains), maize and sorghum (C4 grains) and soybeans and field peas (C3 legumes).

The results showed a significant decrease in the concentrations of zinc, iron, and protein in C3 grains. For example, zinc, iron, and protein concentrations in wheat grains grown at the sites were reduced by 9.3%, 5.1%, and 6.3% respectively, compared with wheat grown at ambient CO2. Zinc and iron were also significantly reduced in legumes; protein was not.

The researchers say that the most significant finding is that C3 grains and legumes lost iron and zinc. Myers and his colleagues estimate that two to three billion people around the world receive 70 percent or more of their dietary zinc and/or iron from C3 crops, particularly, he says, in developing nations, where zinc and iron deficiency is already a major health concern.

Consistent with underlying plant physiology, C4 crops appeared to be less affected by higher CO2 levels, because, the researchers note, “C4 plants concentrate CO2 inside the cell for photosynthesis so they might be expected to be less sensitive to extracellular changes in CO2 concentration.”

The most surprising part of the study was that zinc and iron varied substantially across cultivars of rice. According to the researchers, that suggests that there could be an opportunity to breed reduced sensitivity to the effect of elevated CO2 into crop cultivars in the future.

Myers says that in addition to efforts to reduce CO2 emissions, breeding cultivars with reduced sensitivity to CO2, biofortification of crops with iron and zinc, and nutritional supplementation for populations most impacted could all play a role in reducing the human health impacts of these changes. “Humanity is conducting a global experiment by rapidly altering the environmental conditions on the only habitable planet we know. As this experiment unfolds, there will undoubtedly be many surprises. Finding out that rising CO2 threatens human nutrition is one such surprise,” he says.