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Rising carbon will mean shrunken harvests

Higher carbon dioxide levels in the atmosphere don’t just mean a warmer world: they could also mean both shrunken harvests and a less nourishing diet.

A greenhouse world could be a more malnourished one, trying to survive on shrunken harvests. Researchers have confirmed that as carbon dioxide ratios in the atmosphere double later this century, the protein, iron and zinc content of many of the world’s staple crops could dwindle by between 3% and 17%.

Since an estimated two billion people are already affected in some way by hunger or malnutrition, the consequences are alarming. An extra 175 million people could become deficient in dietary zinc – a vital trace element in plant foods. An additional 122 million people will no longer get enough protein.

And 1.4 billion children below the age of 5 and women of child-bearing age already live in regions where the prevalence of anaemia reaches 20%, and stand to lose 4% of their dietary iron intake.

Almost two thirds of all the world’s dietary protein is provided by plants, along with four-fifths of its dietary iron and more than two thirds of the dietary zinc.

Human civilisation and human food staples – wheat, rice, maize, potatoes, fruit, brassicas, beans and nuts – evolved together, and for most of human history carbon dioxide ratios in the atmosphere hovered around 280 parts per million. But since the start of the Industrial Revolution, these have reached 400ppm.

Two US scientists report in the journal Nature Climate Change "Impact of anthropogenic CO2 emissions on global human nutrition" ,  that they used computer simulations to look at the effect of extra carbon dioxide – the consequence of ever-increasing combustion of fossil fuels over the past 200 years – on the nutritional value of 225 different foods in the population of 151 countries around the planet. They settled on an upper limit of 550ppm of CO2 in the atmosphere by 2050 as their test case.

And they found that the prevalence and severity of nutritional deficiency would be increased worldwide, particularly in Africa, south and south-east Asia and the Middle East. Read the further from