Rising CO2 levels could reduce nutrition values of staple crops like wheat, rice and soy

Some of the world’s most important staple crops could be rendered less nutritious by rising levels of carbon dioxide in the atmosphere, scientists have said, leading to a rise in dietary deficiencies already responsible for hundreds of thousands of deaths annually.

Crops such as wheat, rice and soybeans were all found to have decreased concentrations of iron and zinc when exposed to the higher levels of CO2. Experts said that the effect, which has been observed before but never conclusively proven in the field, represents “a significant threat to human nutrition”.

Scientists have already warned over the impact that rising CO2 levels and global warming could have on crop yields, and the latest findings will only increase fears over global food security.

Worldwide, two to three billion people depend on wheat and rice for most of their iron and zinc intake.

Zinc deficiency is already linked to around 800,000 deaths among under-fives, in whom it can seriously exacerbate such conditions as diarrhoea, pneumonia and malaria, while iron deficiency is the main cause of anaemia, a condition that contributes to around one in every five maternal deaths around the world.

In the first study to find conclusive evidence of the effect of elevated CO2 levels on crop nutrients, scientists from Harvard University exposed 41 different varieties of crop to the kind of CO2 levels anticipated to exist by 2050, given current rates of emission.

“Humanity is conducting a global experiment by rapidly altering the environmental conditions on the only habitable planet we know,” said Dr Samuel Myers, a research scientist at the Harvard School of Public Health and the new study’s lead author.

“As this experiment unfolds there will undoubtedly be many surprises. Finding out that rising CO2 threatens human nutrition is one such surprise.”

In wheat grains, zinc concentrations were reduced by an average of 9.3 per cent across the seven different crop sites used in the study, which was carried out in locations in the USA, Japan and Australia. Iron concentrations were down by 5.1 per cent. Reductions in protein levels were also observed in wheat and rice grains.

The study will be published in the journal Nature tomorrow.

Dr Myers said that the mechanism behind CO2’s impact on nutrient concentrations in plants was not yet known.

There are several possible means of reducing the impact of the newly-observed phenomenon besides cutting CO2 emissions, Dr Myers said, including the development new strains of crop that are less sensitive to CO2 increases, or breeding strains which are high in zinc and iron.