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Cambridge Global Food Security

A Strategic Research Initiative of the University of Cambridge

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Increased CO2 has worrying consequences for crop plant nutrients

last modified Aug 13, 2015 11:57 AM
Can increased atmospheric CO2 aid food security? It might not be so simple.

by Joanna Wolstenholme, Communications intern

By now it is common knowledge that the levels of CO2 in our atmosphere are rising fast. We have just surpassed the 400ppm mark, one that many scientists and campaigners had called the threshold for ‘dangerous’ levels of CO2, which will likely lead to many interlinked climate changes. Yet, it has also been held that whilst on the whole rising CO2 is very bad for the climate, it could in some ways aid food security, by increasing the rates of plant growth. Plants are limited, at least partially, by the levels of CO2 available to them, as CO2 is a main reactant in photosynthesis. Indeed, in commercial hothouses, plants are often ‘fertilised’ with additional CO2 – and we are now effectively doing that on a worldwide scale. However two recent papers have suggested that things may not be so simple.

Feng et al (2015) looked at nitrogen levels of plants grown at elevated concentrations of CO2, and found that they were negatively correlated - nitrogen levels in the plant decreased by 10-12% when CO2 in the atmosphere increased, even in species where no additional growth was seen at elevated CO2. This is worrying as nitrogen is the main building block of protein, which is a vital part of the human diet. Protein deficiency is already an issue in many areas of the world, where the poor rely on grain-based and protein-deficient diets. Ironically the rich – who are in the most part generating such changes in CO2 through their fossil-fuelled lifestyles – are unlikely to be affected by changes in protein in crop plants, as they are able to enrich their diets with meat and other protein rich foods.

Additionally, Myers et al (2014) have found that increased CO2 can lead to lower levels of zinc and iron in grains and legumes. Already an estimated two billion people suffer from deficiencies in these minerals, and this looks set to become worse.

This new research is a stark reminder of the many and varied impacts of increased CO2 on food security, and a warning that there may well be other, even more subtle impacts still to be discovered. It also further emphasises that it is not enough to provide the world with enough calories – food must also be nutritionally complete.