A new study shows that rising levels of planet-warming gases may reduce important nutrients in food crops. Researchers studied the effects of one such gas -- carbon dioxide -- on rice. The researchers grew rice plants in a controlled environment. They set carbon dioxide levels to what scientists are predicting for our planet by the end of the century. They found that the resulting rice crops had lower than normal levels of vitamins, minerals and protein. The researchers said the effects of planet-warming gasses would be most severe for the poorest citizens in some of the least developed countries. These people generally eat the most rice and have the least complex diets, they noted. A report on the study was published in the journal Science Advances.