The international new data, published in Nature, comes only weeks after another study linked climate change and increasing levels of carbon dioxide (CO2) to a reduction in the nutritional quality of food crops . This time, researchers from Australia, Japan, Israel and the US looked at the effects of increased CO2 on the nutrient levels of food crops - revealing that the nutritional quality of a number of the world's most important crop plants dropped in response to CO2 levels raised to those expected by 2050.
“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,” said Samuel Myers, research scientist in the Department of Environmental Health at HSPH and the study’s lead author.
Myers and his team at multiple varieties of wheat, rice, field peas, soybeans, maize and sorghum grown in fields with atmospheric carbon dioxide levels like those expected in the middle of this century. They raised CO2 levels to 550 parts per milion (ppm) levels in open-air fields using a system called Free Air Concentration Enrichment (FACE), which pumps out, monitors and adjusts ground-level atmospheric CO2 to simulate future conditions.
"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)," explained Professor Andrew Leakey from the University of Illinois, who also worked on the study. "And zinc and iron deficiency is a big global health problem already for at least 2 billion people."
The study contributed "more than tenfold more data regarding both the zinc and iron content of the edible portions of crops grown under FACE conditions" than available from previous studies, the team added.
Zinc and iron was reduced significantly in wheat, rice, field peas and soybeans. Wheat and rice also saw notable declines in protein content at higher CO2, they said.
"Across a diverse set of environments in a number of countries, we see this decrease in quality," Leakey explained.
However, the team also noted that nutrient levels in sorghum and maize remained relatively stable at higher CO2 levels because these crops use a type of photosynthesis, called C4, which already concentrates carbon dioxide in their leaves.
"C4 is sort of a fuel-injected photosynthesis that maize and sorghum and millet have," he said. "Our previous work here at Illinois has shown that their photosynthesis rates are not stimulated by being at elevated CO2. They already have high CO2 inside their leaves."
He added that more research is needed to determine how crops grown in developing regions of the world will respond to higher atmospheric CO2: "It's important that we start to do these experiments in tropical climates with tropical soils, because that's just a terrible gap in our knowledge, given that that's where food security is already the biggest issue," he said.