Rising levels of carbon dioxide (CO2 ) in the atmosphere are likely to rob some of the world’s most important food crops of nutrients, scientists have warned.
Wheat, rice, soya beans and field peas all suffered significant losses of zinc and iron in experiments which exposed them to higher concentrations of the greenhouse gas.
In addition, notable declines in protein content were seen in wheat and rice.
US lead scientist Samuel Myers, from the Harvard School of Public Health, said: “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.
“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.”
The Free Air Concentration Enrichment (Face) open-air field trials adjusted ground-level CO2 to simulate expected future conditions.
Other growing conditions, including sunlight, soil, water and temperature, remained unchanged.
Atmospheric CO2 concentrations are currently approaching 400 parts per million (ppm). Industrial emissions are predicted to raise them to 550 ppm by 2050.
The researchers, whose findings are reported in the journal Nature, analysed data from seven different Face experiments in Japan, Australia and the US.
Humanity is conducting a global experiment by rapidly altering the environmental conditions on the only habitable planet we know
Levels of CO2 used in the tests ranged from 546 to 586ppm. Zinc, iron and protein concentrations in wheat grains were reduced by 9.3 per cent, 5.1 per cent and 6.3 per cent respectively compared with those grown under normal conditions. Nutrients in sorghum and maize remained relatively stable at higher CO2 levels because of the type of photosynthesis they employ.
“When we take all of the Face experiments we’ve got around the world, we see that an awful lot of our key crops have lower concentrations of zinc and iron in them (at high CO2),” said co-author Andrew Leakey, from the University of Illinois, US. “And zinc and iron deficiency is a big global health problem already for at least two billion people.”
He added that more research was needed, especially focusing on tropical climates with tropical soils.
“That’s just a terrible gap in our knowledge, given that that’s where food security is already the biggest issue,” he said.