Rising carbon dioxide emissions are set to make the world’s staple food crops less nutritious, according to new scientific research, worsening the serious ill health already suffered by billions of malnourished people.

The surprise consequence of fossil fuel burning is linked directly to the rise in CO levels which, unlike some of the predicted impacts of climate change, are undisputed. The field trials of wheat, rice, maize and soybeans showed that higher CO levels significantly reduced the levels of the essential nutrients iron and zinc, as well as cutting protein levels.

“We found rising levels of CO are affecting human nutrition by reducing levels of very important nutrients in important food crops,” said Prof Samuel Myers, an environmental health expert at Harvard University, Boston, and lead author of the study. “From a health viewpoint, iron and zinc are hugely important.”

Iron and zinc deficiencies

Myers said two billion people already suffer iron and zinc deficiencies around the world. This causes serious harm, in particular to developing babies and pregnant women, and currently causes the loss of 63m years of life annually. “Fundamentally the concern is that there is already an enormous public health problem and rising CO in the atmosphere will exacerbate that problem further.” While wheat, rice, maize and soybeans are relatively low in iron and zinc, in poorer societies where meat is rarely eaten they are a major source of the nutrients. About 2.4 billion people currently get at least 60 per cent of their zinc and iron from these staples and it is over 75 per cent in Bangladesh, Iraq and Algeria.

“This is yet another example of the impact climate change is already having on people’s ability to grow and access the nutritious food they need,” said Hannah Stoddart, Oxfam’s head of policy for food and climate. “With 25 million more children under five at risk of malnutrition by 2050 because of climate change, action to cut emissions and support communities to adapt is crucial.”

The research, published in the journal Nature, represents a major advance in the understanding of how rising CO levels affect food nutrition. The scientists compared nutrient levels in field crops grown in ambient CO levels, about 380-390 parts per million (ppm) at the time of the work, with those grown in the elevated CO levels expected by 2050. The latter level, 545-585ppm, is expected even if substantial curbs on emissions are put in place by the world’s governments. In order to take account of variable growing conditions, the researchers analysed 41 different strains grown in seven locations on three different continents.

Wheat grown in high CO levels had nine per cent less zinc and five per cent less iron, as well as six per cent less protein, while rice had three per cent less iron, five per cent less iron and eight per cent less protein. Maize saw similar falls while soybeans lost similar levels of zinc and iron but, being a legume not a grass, did not see lower protein.

The precise biological mechanism that causes nutrient levels to fall is not well understood as yet. But Professor Brian Thomas, a plant development expert at the University of Warwick and not involved in the research said: “The work is convincing and consistent with what we do know about the plant physiology.” The impact on human health resulting from the drop in the level of protein is less clear than for the zinc and iron loss. — © Guardian Newspapers Limited, 2014