The 21st century is set to see rising levels of carbon in the atmosphere. The atmospheric carbon dioxide content is now 410 parts per million, a rise from 280 ppm in the mid-18th century and 300 ppm in 1950.

While the governments of the world have got together to limit the release of CO2 by cities and industry, the rise is expected to continue till the end of the century.

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Human population, which would keep increasing for most of this period, would compound the problem by greater demand for food and increasing pressure on land use.

Matthew R Smith and Samuel S Myers from the Harvard TH Chan School of Public Health, at Boston, and the Harvard University Center for the Environment, write in the journal, Nature Climate Change, that apart from shortages of food and land to grow food, the rising CO2 levels would affect vital nutritional components of food crops.

The most vulnerable populations of the world, which depend on vegetal sources, would face a double challenge of shortage of food and depleted quality. The data that the study reports puts the spotlight on India as the leader in conditions that need urgent attention.

The current trends of emission from fossil fuels and the changes in land use, worldwide, are expected to take CO2 levels to a disastrous 940 ppm by the century end. Mitigation measures that are proposed and which may be implemented, would lead to slower rise of CO2, as shown in the graph.

But, as we can see, all programmes, except the most ambitious one, would reach a CO2 level of 550 ppm. For the purpose of the present study, of the effect of CO2 on nutrients in food crops, the paper takes it that the rise in CO2 would follow the current trajectory, and reach the level of 550 ppm by the year 2050.

Experimental trials have been carried out, the paper says, with food crops that are grown in open field, both under ambient conditions and under conditions where CO2 levels are at about 550 ppm. The trials reveal that in many important crops, the concentration of protein, iron and zinc falls by some three to 17 per cent.

The paper says that the source of most of these important nutrients, for humans worldwide, is plant-based food. As much as 63 per cent of dietary protein, 81 per cent of iron and 68 per cent of zinc, the paper says, come from vegetal sources.

There is already severe nutritional deficiency, worldwide — over two billion people are estimated to be deficient in at least one essential nutrient. This is a condition that has cascading implications — of poor health, rising medical costs and low productivity. A fall in the nutritional content of plantbased food would hence exacerbate the problems, of which the third world would bear the greatest brunt.

In order to assess the impact of climate change and elevated CO2, the current study has integrated the best available estimates of population growth, physiological nutritional requirements and future diets. The effect on the nutrient content of a large number of kinds of food — 225, against 98 used in earlier studies — has then been modelled.

Age and sex-specific data sets have been used and data from sources selected to enable comparison and analysis. “With the enhancement and harmonisation of datasets and assumptions, we have attempted to provide the most accurate synthesis of the global health burden from elevated CO2-related nutrient shifts in crops,” the paper says.

After going through the findings, one can see that India leads in the increase in nutrient deficiency, followed by China. Latin America, Central Asia, North and sub-Saharan Africa and the rest of Asia are not far behind. The effect is to add to the pressures on the areas that are already under the highest stress.

Apart from impaired productivity and higher health care costs, are the human costs of infant and premature, diet-related, adult mortality. The economic impact, according to “Global Impact”, an independent group of experts, comes to US$ 3.5 trillion per year, or US$ 500 per individual, worldwide.

The findings underline another area where many parts of the world need to adapt while coping with climate change. The study notes that the diets and health of global populations are changing rapidly. Nutrition experts and planners need to take the effects of enhanced CO2 on the nutritional value of plant foods into account and influence choices to reduce impact.

The writer can be contacted at response@simplescience.in