This week’s report that the Antarctic ice sheets are in irreversible retreat grabbed headlines, but another report last week warned that rising carbon dioxide levels threaten the quality of the world’s food supply, as well.
Increased malnutrition and loss of life — due to declining levels of dietary zinc, iron, and protein in important food crops — will occur around the world as elevated atmospheric CO2 climbs to levels that are anticipated by 2050, reports an international team led by researchers at Harvard University and including UC Davis plant scientist Arnold Bloom. The study appeared online May 7 in the journal Nature.
Confirmation of this link between rising CO2 and declining crop nutrient content is particularly sobering for developing nations, where an estimated two billion people already suffer from zinc and iron deficiencies.
“This study indicates that the reduction of these nutrients in important grain and legume crops is one of the most significant health threats that has ever been shown to be associated with climate change,” Bloom said.
The researchers analyzed data from 41 cultivated varieties of grains and legumes grown in seven locations in Japan, Australia and the United States. The test crops were grown in open fields, rather than in greenhouses or growth chambers. In these experimental fields, CO2 levels were monitored and pure CO2 added, using a technology called “free air carbon dioxide enrichment.” This process maintained the CO2 levels in the range of 546-586 parts per million across all seven sites. Today CO2 levels are normally around 400 parts per million.
At harvest, the researchers tested the nutrient concentration of the edible portions of wheat and rice, maize and sorghum, and soybeans and field peas. The results showed significant decreases in the concentrations of zinc, iron and protein in wheat grains grown at the test sites — 9.3 percent, 5.1 percent and 6.3 percent respectively — compared to wheat grown at naturally occurring CO2 levels. In the experimental legume plots, zinc and iron also decreased significantly but protein did not.
Earlier this year, Bloom and another team of researchers demonstrated that elevated levels of carbon dioxide inhibit plants’ assimilation of nitrate into proteins. Those findings, published in the journal Nature Climate Change in April, also provide evidence that the nutritional quality of food crops is at risk as climate change intensifies.
Contributed by Pat Bailey