Carbon dioxide is an essential nutrient for plants. It has been surmised that increasing concentrations of carbon dioxide in the atmosphere may increase plant productivity and hence the amount of food they provide. Research from China published recently in the peer-reviewed PLOS One of the Public Library of Science in the US suggests that this will not occur.
The research was carried out with strawberry plants. June-bearing strawberries are an important food crop in many countries. Higher average temperatures are known to reduce yields. Elevated carbon dioxide concentrations alone improve fruit yield and quality but reduce total antioxidants in strawberry fruit.
However, the research shows that elevated carbon dioxide together with elevated temperature reduces fruit yield. Application of nitrogen fertilizer, an essential nutrient for plants, at elevated temperatures further decreases fruit production.
Parallel reports are coming in of similar behaviour in other food crops. While much more research will follow, it appears already that it would be wrong to think that higher carbon dioxide levels will lead to higher production from food crops.
The strawberry study is available at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0041000#s3