Rising carbon dioxide levels affect nutrients in crops, study says

Wheat grown in an environment with a higher concentration of carbon dioxide yielded lower protein levels, according to a study approximating the expected CO2 levels of the future.
Wheat grown in an environment with a higher concentration of carbon dioxide yielded lower protein levels, according to a study approximating the expected CO2 levels of the future.
(David Karp / Los Angeles Times)

The increased concentration of carbon dioxide that comes with climate change could mean some basic food plants will carry lower concentrations of iron and zinc – and deficiencies of those nutrients are already a “substantial global public health problem,” scientists reported Wednesday.

The scientists studied grains and legumes grown at the elevated atmospheric concentrations of carbon dioxide predicted for the middle of this century. They conducted a meta-analysis of data from their own study and previous ones, looking at 143 comparisons of the edible portions of crops at both ambient levels of carbon dioxide and elevated levels of 546 to 586 parts per million.

Carbon dioxide in the atmosphere is expected to reach 550 ppm in the next four to six decades. The lead scientist on the study, Samuel Myers of the Harvard School of Public Health, said by telephone that the issue should be of concern to people no matter their views on climate change.


The work was done at seven sites in Japan, Australia and the United States. The scientists tested rice, wheat, maize, soybeans, field peas and sorghum over several growing seasons.

“We found that elevated carbon dioxide was associated with significant decreases in the concentrations of zinc and iron,” the researchers said in the journal Nature.

The wheat had 9.3% lower zinc and 5.1% lower iron at the elevated levels, for example. And the protein content was 6.3% lower in wheat and 7.8% lower in rice, the researchers reported. Maize and sorghum had no significant change, and there was a small decrease in protein in field peas, they said.

“[W]e find that the edible portions of many of the key crops for human nutrition have decreased nutritional value when compared with the same plants grown under identical conditions but at the present ambient” carbon dioxide, the researchers said.

An estimated 2 billion people are deficient in zinc and iron, leading to a loss of 63 million life-years annually, the scientists said. And, according to the United Nations Food and Agriculture Organization, 2.3 billion people live in countries where at least 60% of the dietary zinc and iron comes from the affected grains and legumes.

Decreases in protein, the researchers said, could lead to increased risk of hypertension, heart disease and other problems.


The major micronutrient deficiencies globally are iron, zinc and vitamin A, Myers said. Vitamin A generally comes from produce, and he said he didn’t know of any efforts to look at effects on it of elevated carbon dioxide.

As for solutions, Myers noted that iron and zinc fortification and supplementation programs have existed for years and not solved the problems. Alternatively, work is underway to develop biofortified crops and to develop new cultivars that are less sensitive to the elevated carbon dioxide levels, he said.

“We note, however, that such breeding programs will not be a panacea for many reasons, including the affordability of improved seeds and the numerous criteria used by farmers in making planting decisions that include taste, tradition, marketability, growing requirements and yield,” they wrote.

A rice called Golden Rice, which was fortified with vitamin A, was a cautionary tale, Myers said, because “the adoption has been less than hoped.” That, he said, does not mean such work should be stopped.

“I think it’s a mistake to take too many arrows out of our quiver,” he said, when efforts to feed the world will encounter problems ahead including water scarcity, soil degradation and elevated carbon dioxide.