In "The Great Nutrient Collapse," Helena Bottemiller Evich reports that "the atmosphere is literally changing the food we eat, for the worse. And almost nobody is paying attention."
[P]lants change in important ways when they’re grown at elevated CO2 levels. Within the category of plants known as “C3”―which includes approximately 95 percent of plant species on earth, including ones we eat like wheat, rice, barley and potatoes―elevated CO2 has been shown to drive down important minerals like calcium, potassium, zinc and iron. The data we have, which look at how plants would respond to the kind of CO2 concentrations we may see in our lifetimes, show these important minerals drop by 8 percent, on average. The same conditions have been shown to drive down the protein content of C3 crops, in some cases significantly, with wheat and rice dropping 6 percent and 8 percent, respectively.
Read the article here: http://www.politico.com/agenda/story/2017/09/13/food-nutrients-carbon-dioxide-000511