If CO2 levels keep rising as projected, the populations of 47 countries may lose more than 5 percent of their dietary protein by 2050 due to a decline in the nutritional value of rice, wheat, and other staple crops, according to Harvard T.H. Chan School of Public Health researchers. They estimate an additional 250 million people may be at risk of protein deficiency because of elevated CO2 levels. This is the first study to quantify this risk.