Harvard researchers have found that staple crops grown in environments with levels of carbon dioxide (CO2) similar to the levels expected in 2050 had less zinc, iron and protein than crops grown at current CO2 levels. Samuel S. Myers et al., “Increasing CO2 threatens human nutrition,” Nature, May 2014. The researchers conducted field trials of 41 strains of wheat, rice, maize, and soybeans grown in seven locations on three continents, elevating the CO2 levels from the current average of about 380-390 parts per million (ppm) to the expected levels in 2050 of 545-585 ppm. The wheat, rice and maize grown at the higher CO2 levels each had about 5 to 10 percent less zinc, iron and protein, while soybeans lost similar amounts of zinc and iron but maintained current levels of protein. The precise biological reason for the declines remains unclear, but researchers reportedly said that the nutrient reduction could cause a rise in metabolic syndrome in developed countries and exacerbate the iron and zinc deficiencies already experienced by two billion people around the world. See The Guardian, May 7, 2014.