It is well known that plants, using energy from sunlight, make food from carbon dioxide present in the air. So, it is logical to argue that the plants are going to make more food if carbon dioxide levels in the air are going up due to climate change. Research results of a team of US, Australian and Japanese scientists undertaken under the leadership of

Professor Samuel Myers of Harvard University, United States and published recently in Nature however negate this assertion.

The study claims that the carbon dioxide emissions are slowly making the world's staple food crops less nutritious and asserts that wheat, maize, soybeans and rice would witness depletion in the levels of their nutrients iron and zinc, as well as proteins, between now and 2050.

To obtain these results, the team compared nutrient levels in field crops grown in ambient CO2 levels, about 380-390 part per million (ppm) with those grown in the elevated CO2 levels expected by 2050. In order to take account of variable growing conditions, the researchers analysed 41 different strains grown in seven locations on three different  continents.

Due to an unknown biological mechanism, wheat grown in high CO2 levels had 9 percent less zinc and 5 percent less iron, as well as 6 percent less protein, while rice had 3 percent less zinc, 5 percent less iron and 8 percent less protein. Maize and soybeans also  witnessed similar falls but, the latter being a legume it did not show lower protein.

Rice, maize, soybeans and wheat are the main source of nutrients for over 2 billion people living in poor countries. But with climate change and the rising amount of CO2 in the air we breathe, their already low nutrient value compared to meat, for instance, is sure to decrease.

The study found that rising level of CO2 is affecting human nutrition by reducing levels of very important nutrients in very important food crops. From a health viewpoint, iron and zinc are hugely important and close to one third of the world's population already suffers from iron and zinc deficiencies, and according to this new study the rising levels of CO2 would only make things worse.

The impact on human health resulting from the drop in the level of protein is less clear than for the zinc and iron loss. It could however increase the rate of metabolic syndrome, diabetes, heart disease and stroke.

The study negates the possibility that the affected populations could meet zinc and iron requirements just by eating more staple foods. The food production the study asserts has to already double by 2050 in order to meet the demand of rising populations. And while some of the varieties used in the research performed better than others, breeding programmes focused on these traits would not be a panacea for many reasons including the affordability of improved seeds and the numerous criteria used by farmers in making planting decisions that include taste, tradition, marketability, growing requirements and yield.

As to the relationship between increased CO2 levels and improved crop yields the study indicates little positive effect.